Physics Unit 3
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Transcript of Physics Unit 3
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Physics Unit 3
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Year Long Plan
First Ten Minutes (Everyday) – Revision, questions
Then Learning/Pracs Homework… 40+ Club
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What you need
Textbook Student Book Scientific Calculator
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Topics
Unit 3: Motion Electronics and Photonics
Unit 4: Electric Power Interaction of light and matter
Detailed Study (Homework) …Plus an extra project…?
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Project…?
Print off News article. Youtube video
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Area of Study One
Motion in One and Two Dimensions
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The Plan
Review of Motion Projectile Motion Momentum Energy Circular Motion Gravity and Satellites
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Review of Motion
Place the following into a linked “Concept Map”. Label all the arrows that link the concepts together.
Forces, Newton’s First Law, Newtons Second Law, Newton’s Third Law, Eqns of motion, mometum, velocity, acceleration, Impulse, Work, kinetic energy, potential energy, Types of forces, Gravity, Normal Force, Springs, Inclined Planes
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Review
CUPS 2
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Scalars and Vectors
Scalar: Physical quantity represented by only a number
Eg Mass, temperature Vector: Physical quantity requiring a
direction AND number (magnitude) Eg Force, velocity
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Distance and Displacement
e.g. total distance of travel
• DistanceLength of an object has travelled
• Displacement
e.g. final position – initial position
Change in position of an object.
Scalar
Vector
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Speed or Velocity?
Speed: Scalar quantity.
Velocity: Vector quantity. Magnitude AND Direction
Magnitude only
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Velocity
To find velocity, when travelling at a constant velocity (no acceleration) OR to find the average velocity:
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Questions
Tim travels 80m North up North Rd. He then turns and travels 60m East along east road. This travel takes 24s.
1) Draw a diagram of the situation2) Calculate the total distance3) Calculate the total displacement4) Calculate the average speed5) Calculate the average velocity
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Centre of mass motion
Usain Bolt runs the 100m with a speed of 10ms-1
Do all parts of his body move at 10ms-
1? His arms? His legs? His Head? No. His arms often move faster (and
slower) than 10ms-1
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Centre of Mass Motion
As physicists, we simplify the problem, and approximate Usain Bolt as a point, at his centre of mass.
So all calculations of his speed are based on his centre of mass
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Joke
A Statistician, Engineer and Physicist go to the horse track. Each have their system for betting on the winner and they're sure of it. After the race is over, the Statistician wanders into the nearby bar, defeated. He notices the Engineer, sits down next to him, and begins lamenting: "I don't understand it. I tabulated the recent performance of all these horses, cross-referenced them with trends for others of their breed, considered seasonal variability, everything. I couldn't have lost.“ "Yeah," says the Engineer, "well, forget that. I ran simulations based on their weight, mechanical ratios, performance models, everything, and I'm no better off.“ Suddenly, they notice a commotion in the corner. The Physicist is sitting there, buying rounds and counting his winnings. The Engineer and Statistician decide they've got to know, so they shuffle over and ask him, "what's your secret, how'd you do it?“ The Physicist leans back, takes a deep breath, and begins, "Well, first I assumed all the horses were spherical and identical..."
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Acceleration
Acceleration is a measure of how much velocity changes over time
Change in velocity: Acceleration:𝑎=
𝑣−𝑢𝑡
=Δ𝑣𝑡
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Graphing motion
We can graph either the displacement, velocity, acceleration as time changes
The Gradient of a graph is the slope.
The area under the graph is the solid area between the line and the axis
Eg …
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Positive Slope/ Gradient
Zero Slope/ Gradient
Negative Slope/ Gradient
Area under graph
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Graphing Motion
Prac: Graphing Motion
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Displacement-Time Graph
A puppy runs after a stick. It runs 10m to the stick (it takes 10s). It then waits by the stick for 10s, and finally brings the stick back to its owner over 10s.
Draw a displacement-time graph for this scenario
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Displacement-Time Graph
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Displacement-Time Graphs
Gradient of the displacement-time graph is the velocity
Questions:1) Calculate the velocity over the first 10s2) Calculate the velocity over the next 10s3) Calculate the velocity over the last 10s4) Calculate the average velocity over the
full 30s
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Velocity-Time Graph
Gradient of a velocity-time graph is acceleration
Area under the velocity graph is the displacement
Eg…
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Velocity-Time Graph
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Velocity-Time Graph
1) What is the initial velocity?2) What is the change in velocity over
the 30s of motion3) What is the acceleration?4) Is this a constant acceleration?5) What is the total displacement
between 0 and 30s?
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Acceleration-Time Graph
The area under an acceleration-time graph is the change in velocity.
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Acceleration-Time Graph
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Acceleration-Time Graph
1) What is the acceleration at 0s?2) What is the acceleration at 10s?3) What could this graph be describing?4) Find the change in velocity between 0s
and 10s5) If the initial velocity is 2ms-1, what is
the velocity after 10s?
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Questions
Draw a displacement-time, velocity-time, and acceleration-time graph for the following:
Sky diver – no air resistance Sky diver – air resistance Person walking at a constant speed
along a path Person 20m away from their house,
standing still
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Equations of Motion
Any object moving with a constant acceleration, use the equations of motion
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Example
A car accelerates from rest for 10s at an acceleration of 1.5ms-2
What is the final speed? What distance does the car travel over
this time
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Questions
1) A car, travelling at 30ms-1, accelerates to 40ms-1 in order to pass a slower car. This acceleration takes 20s. What distance does he travel during this acceleration?
2) Q4 [Pg 12] A car travelling at a constant speed of 80km/h passes a stationary motorcycle policeman. The policeman sets of in pursuit, accelerating uniformly to 80km/h in 10s and reaching a constant speed of 100km/h after a further 5s. At what time will the policeman catch up with the car.
3) Extension question: Mr McGovern is driving down a country road at 100km/h when a beautiful duck steps out 75m in front of his car. His reaction time is 0.6s, then he applies the brakes, decelerating at 15ms-2. Will the duck live?
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Vertical Motion
Vertical motion is accelerated motion where the acceleration equals gravity (10ms-2)
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Vertical Motion
How high does the tennis ball go?1) Time how long it takes to get to the top of
its flight2) What was the initial velocity?3) How high did the ball go?
4) After the ball left the hand, draw the forces acting on it
5) When the ball was at the top of its flight, draw the forces acting on it
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Question
A footy ball is kicked vertically upwards with an initial speed of 22ms-1
How high does it reach? After what time does it hit the ground
again?
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Forces
When we add all the forces acting on a body, we add the forces head to tail
eg
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Forces
The total force is found by drawing a new arrow from the tail of the first to the head of the last
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Find the total forces
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Q3 2012
A metal ring is to be held stationary by three forces. Which configuration would make the ring stationary, and why?
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Newton’s Laws
First Law: Unless acted on by a net force, an object will continue its motion (whether that’s stationary or constant velocity New Name: Second Law: If acted on by a net force,
an object will accelerate New Name:
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Newton’s Laws
Third Law: For every action force on object A, there is an equal and opposite reaction force on object B
New Name:
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Newton’s Laws
Why is there misunderstanding in Newton’s Laws?
Rules for next 6 examples. Quietly think of which answer you like. Text in answer Then we will work together to decide how
most people think… And what Newton’s Laws predict the
answer should be
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Newton’s Laws: Example 1
Victoria Azerenka throws a tennis ball upwards for her serve. Consider the forces on the tennis ball after it has left the hand, but before she hits it on the way down. Is there…?
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Newton’s Laws: Example 1
a) A downwards force of gravity, along with a steady decreasing upwards force
b) A steadily decreasing upward force from the moment it leaves her hand until it reaches its highest point, on the way down a steadily increasing downwards force of gravity
c) An almost constant downwards force of gravity
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Newton’s Laws: Example 1
What do you think the answer is? What do you think most of the general
population will think? What answer does Newton’s Laws
predict?
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Newton’s Laws: Example 2
An elevator is being lifted by a steel cable at a constant speed. The forces on the elevator are…
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Newton’s Laws: Example 2
a) The upwards force of the cable is greater than the downward force of gravity
b) The upwards force of the cable is equal to the downwards force of gravity
c) The upwards force of the cable is smaller than the downwards force of gravity
d) None of the above: The elevator goes up simply because the cable is being shortened
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Newton’s Laws: Example 2
What do you think the answer is? What do you think most of the general
population will think? What answer does Newton’s Laws
predict?
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Newton’s Laws: Example 3
A big truck and a small car collide head on.a) The truck exerts a bigger force on the
car than the car onto the truckb) The car exerts a bigger force on the
truck than the truck on the carc) The truck exerts a force on the car, but
the car doesn’t exert one on the truckd) They exert an equal force on each other
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Newton’s Laws: Example 3
What do you think the answer is? What do you think most of the general
population will think? What answer does Newton’s Laws
predict?
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Newton’s Laws: Example 4
A stationary ice hockey puck is hit. It travels in a straight line along the frictionless ice.After leaving the hockey stick, does the puck …?a) Speed up as there is no frictionb) Travel at a constant speed, and would only
be stopped by the edge of the ice rinkc) Slow down as the force of gravity works
against itd) Slows down as it runs out of force from the
hockey stick hit
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Newton’s Laws: Example 4
What do you think the answer is? What do you think most of the general
population will think? What answer does Newton’s Laws
predict?
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Newtons Laws: Example 5
The same puck is travelling at a constant speed from (a) to (b). At (b) another stick gives it a swift hit in the direction shown. What is the new direction of the puck?
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Newton’s Laws: Example 5
What is the new direction of the puck?
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Newton’s Laws: Example 5
What do you think the answer is? What do you think most of the general
population will think? What answer does Newton’s Laws
predict?
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Newton’s Laws: Example 6
Demo: A pulley is set up with a string connecting two weights of equal masses. But the masses are at different heights. What happens…?
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Newton’s Laws: Example 6
a) Nothing movesb) The mass on the right pulls down (and the
mass on the left goes up), but at a constant speed
c) The mass on the right pulls down (and the mass on the left goes up), but at an accelerated rate.
d) The mass on the left pulls down (and the mass on the right goes up), but at a constant speed
e) The mass on the left pulls down (and the mass on the right goes up), but at an accelerated rate.
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Newton’s Laws: Example 6
What do you think the answer is? What do you think most of the general
population will think? What answer does Newton’s Laws
predict?
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Newton’s Third Law
Recall: For every action force on object A, there is an equal and opposite reaction force on object B
What is the action/reaction pair for … Eg
Force on car is equal and opposite to force on truck
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Newton’s Third Law
What is the action/reaction pair for … [Hint: Draw each situation first]
Hitting a hockey puck Jumping up (at the moment of jumping) Falling back down… A book on a table
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Newton’s Third Law
Common misconception… The action/reaction pair for gravity is
NOT the normal force… Why? They are acting on the same
body!(Draw 1N book, 10N table)
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Experiment
Forces, Pulleys and String
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Newton’s Laws
CUPS 3, 4, 5. [Monash University] Reminder, print A3 sheets
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Inclined Plane
Experiment
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Normal Force and Inclined Planes
A normal force (FN or N) always acts at RIGHT ANGLES to a surface.
Draw in the normal forces acting on the circles below:
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Normal Force on an Incline
Draw the force of gravity on the ball Is the normal force
bigger/same/smaller than gravity?
Fg
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Normal Force on an incline
We know that the ball accelerates down the ramp. So the normal doesn’t balance out gravity!
Draw the direction of acceleration Draw in the direction of the total force
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Normal Force on an incline
Show how the two forces acting on the ball add to give the total force
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Normal Force on an Incline
Draw in the right angle Draw in the angle of the ramp What is the size of the total force?
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Questions from Exams
Sample Q 3b Sample Q 6a & 6c 2012 Q 4a, b 2012 Q 5a – d 2011 Q 7, 8
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Projectile Motion
… And the effects of air resistance
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Projectile Motion
Projectile motion is made simple because we can deal separately with an object’s horizontal and vertical components of its velocity.
𝑣=20𝑚𝑠−1
45o
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Projectile Motion
𝑣 𝑥
𝑣=20𝑚𝑠−1
45o
𝑣 𝑦
𝑣=20𝑚𝑠−1
45o
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Projectile Motion
𝑣 𝑥
𝑣=20𝑚𝑠−1
45o
𝑣 𝑦
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Projectile Motion
Find the vertical and horizontal components of the golf balls velocity if it had an initial velocity of 20ms-1, and angled at 20o to the horizontal.
a) Draw the diagramb) Work out vertical component of velocityc) Work out horizontal component of velocityd) Do your answers make sense?
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a)b) c) d) Of course!
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Projectile Motion
Find the vertical and horizontal component of a mortar round if it is fired at an angle of 75o to the horizon at a speed of 140ms-1
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Projectile Motion
Why did we split up the velocity into horizontal and vertical components? Because gravity only acts on the
vertical component Therefore horizontal component stays
at constant velocity
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Projectile Motion
Horizontal Component of Velocity: Use Vertical Component of Velocity: Use the
equations of motion
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Vertical Drop
0s
1s
2s
3s
4s
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Projectile
0s
1s
2s
3s
4s
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Compare the two
0s
1s
2s
3s
4s
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Projectile Motion
Horizontal Component of Velocity: Use Vertical Component of Velocity: Use the
equations of motion
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Projectile Motion
Golf ball hit had an initial velocity of 20ms-1, and angled at 20o to the horizontal. How far does it go before hitting the ground? (Assume no air resistance)
𝑣=20𝑚𝑠−1
20o
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Projectile Motion
Use y-component of velocity. Need to use an equation of motion
Work out v first
Why two answers?
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Projectile Motion
Now t.
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Projectile Motion
Now use t with the horizontal component of velocity to work out the horizontal distance
Don’t give up your day job if that is as far as you can hit!
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Projectile Motion
Summary: Split initial velocity into horizontal and
vertical components Horizontal component uses v=x/t Vertical component uses equations of
motion
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Question
Golf ball hit had an initial velocity of 50ms-1, and angled at 35o to the horizontal. How far does it go before hitting the ground? (Assume no air resistance)
𝑣=50𝑚𝑠−1
35o
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Questions
Sample – Q5 a & b 2011 – Q 12 and 13
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2011 Q12 and 13
Domenic fires a toy cannon, and the projectile leaves the barrel with a velocity of 24 ms-1 at an angle of 37o to the horizontal as shown. Ignore air resistance
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2011 Q12 and Q13
How long does it take for the projectile to move from point A to point B?
What is the maximum height of the trajectory?
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Projectiles and Air resistance
When you account for air resistance in projectile motion, how does it change the trajectory?
Demo Draw trajectory
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Happy Gilmour Golf
After the stunning success of your last project: Angry Shapes, the game designer has come back to you with a fresh project: Happy Gilmour Golf
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Chapter 2 – Collisions and circular motion
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Momentum
What is momentum? Mass x velocity Units: kgms-1
What is it good for? Analysing collisions or when velocity
has changed
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Conservation of momentum
The reason it is so good for analysing collisions is that…
In a closed system, TOTAL MOMENTUM is CONSERVED
Conserved = Stays the same.
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Concept question example
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Concept Question Example
The man jumps from his boat to the shore.
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What happens to the boat?
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Momentum
Write down what YOU think happens to the boat.
Why..?
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Demo
Demo of what just happened
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Momentum
Before the man jumps, what is his momentum? (Use a word to describe it)
Before the man jumps, what is the boat’s momentum? (Use a word to describe it)
Before the man jumps, what is the combined TOTAL momentum of the boat and man?
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Momentum
When the man is in the air, what is his momentum? (Use a word to describe it)
When the man is in the air, what is the momentum of the boat?
When the man is in the air, what is the combined TOTAL momentum of the boat and the man?
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Conservation of Momentum
When driving his Lamborghini home from school, Mr. McGovern doesn’t notice the car that has stopped in front him, and collides with this car. Before the collision, Mr. McGovern was travelling at 15ms-1. After the collision, the two cars stick together as shown in the figure below, and move with the same speeds. Mr. McGovern’s car has a mass of 2000kg, and the other car has a mass of 1500kg.
Figure 1: Before collision only Mr. McGovern’s car is
moving. After collision both cars stick together and move away at the same speed.
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Momentum
1) What is the total speed of the two car wreck after the collision.
2) First: Plan how you will do this3) Then, do it!
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Questions
Sample Q1a 2012 Q2
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How do we relate momentum to other things in motion?
When is momentum useful for calculating stuff?
Collisions When the momentum is changing. What needs to happen for the
momentum of something to change? A force!
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How do we relate momentum to other things in motion?
So… momentum not helpful when it stays the same
But its helpful when we have a collision, or a change in momentum
How are force and change in momentum related?
ForceChange in momentum
???
Impulse!
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How do we relate momentum to other things in motion?
Change in momentum (lamborgini) = final momentum – initial momentum.
Change in momentum = Impulse = F x t
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Question
Sample Q6 b
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Energy
Types of energy? Two types: Kinetic Potential (stored)
Kinetic Electricity Sound Elastic Gravitational Heat Chemical Elastic Nuclear Light energy Wave
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Energy
Place them into kinetic energy or potential energy
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Energy
Kinetic Energy = Gravitational potential energy = mgh
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Conservation of Energy
Energy can never be created or destroyed, only moved from one form to another.
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Energy
A B
A steel ball rolls along a smooth, hard, level surface with a certain speed. It then smoothly rolls up and over the hill shown below. How does its speed at point B after it rolls over the hill compare to its speed at point A before it rolls over the hill?
a. Its speed is significantly less at point B than at point A.
b. Its speed is very nearly the same at point B as at point A.
c. Its speed is slightly greater at point B than at point A.
d. Its speed is much greater at point B than at point A.
e. The information is insufficient to answer the question.
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Work
Work is defined as: how much an object energy has changed by.
Eg. A 1kg brick is lifted 1m vertically and placed on a table. How much work has been done?
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Work
The work can also be found from the area under a Force-Distance graph
This is especially useful if the force is not a constant force.
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Questions
2012 1a & b 2011 Q14 & 15
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Work 2012 1a and b
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Elastic and inelastic collisions
Elastic collision means that kinetic energy is conserved
Inelastic collision means that kinetic energy is not conserved.
Hang on a minute! How can that be? The energy is still conserved, but it is
transferred to some wasteful form like sound or heat
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Questions
Sample Q 1b
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Springs: Hooke’s law and elastic potential energy
Normal ExtendedCompressed
Δx Δx
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Springs
Demo: What direction is the force from the spring after you extend it and compress it?
Does the force get bigger or smaller the more you compress or extend it?
What could the equation that relates force and extension be?
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Springs: Hooke’s Law
k = spring constant (depends on the spring).
Eg, would this spring have a big spring constant or a little spring constant?
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Springs
Springs can also be used on the horizontal …
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Springs and elastic potential energy
Springs store energy with the equation
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Springs
Demo: Sonic Ranger Draw graphs of … Displacement, velocity, acceleration,
kinetic energy, elastic potential energy, gravitational potential energy, total energy
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Questions
Sample Question 3a -b 2011 Question 16-20
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Circular Motion
Things that travel in a circular motion… Bucket on the end of a string. Moon about the earth Earth about the sun Hammer throw Cyclist in a velodrome Car going around a corner
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Circular Motion
Speed = ?? Speed = distance/time Speed = (2πr)/time
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Circular motion
What about the car’s velocity? Velocity is changing, because as it goes
around the circle, its direction changes! A changing velocity means … Acceleration! Acceleration means there must be a
force!
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Centripetal acceleration
Acceleration in a circle is called “centripetal acceleration”
NOT “centrifugal acceleration”
Substitute in the formula for the speed of an object in circular motion
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Centripetal Acceleration
What is the direction of the acceleration?
Velocity
Velo
city
Velocity
Velo
city
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Centripetal Acceleration
Centripetal Acceleration is always towards the centre
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What happens if we let go of circular motion?
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What happens if we let go of circular motion?
Flies off at tangent
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Question.
A car is travelling around a circular track, and a driver drops his apple core out the window. Litterer! Which direction does it travel as it falls?
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Forces that cause circular motion
Tension force Gravity Friction
What direction must these forces be acting in? F = ma So, in the same direction as the centripetal
acceleration Called the centripetal force (NOT centrifugal!)
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Questions
Sample Q 2
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Example: Circular Motion
1. Calculate the radius of the ball’s path2. Draw all forces acting on the ball3. What is the net force? What is this called4. Calculate the tension force in the string5. How fast is the ball travelling?
Mass = 150g
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Do on board
![Page 147: Physics Unit 3](https://reader038.fdocuments.net/reader038/viewer/2022102510/568130af550346895d96be8d/html5/thumbnails/147.jpg)
1: The radius
![Page 148: Physics Unit 3](https://reader038.fdocuments.net/reader038/viewer/2022102510/568130af550346895d96be8d/html5/thumbnails/148.jpg)
2: Draw the forces on the ball Mass = 150g
Gravity and Tension
![Page 149: Physics Unit 3](https://reader038.fdocuments.net/reader038/viewer/2022102510/568130af550346895d96be8d/html5/thumbnails/149.jpg)
Circular Motion
How do we add forces? Head to tail!
60o
Fg
FT
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Circular Motion
60o FT
FG
1.47N
2.94N
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Circular Motion
Blah
60o FT
FG
1.47N
2.94N
![Page 152: Physics Unit 3](https://reader038.fdocuments.net/reader038/viewer/2022102510/568130af550346895d96be8d/html5/thumbnails/152.jpg)
Recall… Ball on a ramp
Which direction is the acceleration? Which direction is the net force? What forces add together to give the
net force?
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What about a bike on a velodrome wall?
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What about a bike on a velodrome wall?
Draw the direction of the total force (the centripetal force)
Draw the forces that make up this total force
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Circular Motion
What is the difference between this and the ball that rolls down the ramp?
On the ramp, the total force (and acceleration) is down the ramp. On the velodrome, the total force (and acceleration) is towards the centre
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Circular Motion
If on the velodrome, the bike wasn’t moving… what would happen?
Acceleration would be the same as the ball on the ramp and they would roll down the incline!
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Circular motion in a vertical plane
Imagine you are in the roller coaster car below, and it travels with a constant speed of 8ms-1 along the track
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Circular Motion in a vertical plane
Describe what you feel as you get to point A
A
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Circular Motion in a vertical plane
Describe what you feel as you get to point B
B
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Circular Motion in a vertical plane
Lets do the maths… Find the Normal forces on an 80kg
man in the coaster at point A and at point B
The track can be broken into two circular sections, with radii = 10m
10m10m
A
B
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Do on board (together with slides…)
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Circular Motion in a vertical plane
At point A
– This is the total force on the man Direction=upwards What are the two forces that act on the
man in the coaster at A? Gravity and the Normal Force.
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Circular Motion in a vertical plane
Together these two forces add up to 512N
What is the normal force equal to? 1296N
512N
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Circular Motion in a vertical plane
At point B
– This is the total force on the man. Direction = Downwards. So centripetal force is the same, but in
different direction
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Circular Motion in a vertical plane
Together gravity and the normal force add up to 512N
What is the normal force equal to? 272N
512N
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Circular Motion in a vertical plane
So compare the normal forces acting on the man at the two points
How does this compare to what we feel?
272N
A
B
1296N
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Circular Motion in a vertical plane
We feel the roller coaster pushing with a bigger force at point A
At point B, it pushes with a smaller force, we feel more “weightless”
272N
A
B
1296N
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Circular Motion in a vertical plane
Demo: water in the bucket… How to keep the water in the bucket?... What is the minimum speed…?
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Circular Motion in a vertical plane
In order for the water to stay in the bucket (or the people to stay in a roller coaster…), the centripetal acceleration must be equal to, or greater than the acceleration due to gravity
So
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Circular Motion in a vertical plane
Why? If they have a centripetal acceleration
greater than gravity, they move around the roller coaster faster than they “fall”
Eraser example
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Questions
Sample Q 7 2011 Q 4, 5, 6 2011 Q 9, 10, 11
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Chapter 3 – Gravity and satellites
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Does the earth’s gravity extend as far as …?
Do this as a Think pair share…
To a person standing on earth’s surface? A person who jumped in the air? An aeroplane in the sky? Satellites orbiting the earth? The moon? How come weightless in satellites/space
ships?
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Law of gravity
Newton isn’t famous for “discovering gravity”, but for correctly figuring out that the thing that pulls us (and apples) to the surface of the earth, is the same thing that keeps the planets orbiting the sun (and the moon around the earth)
G = 6.67x10-11
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Law of Gravity
If I have a mass of 80kg, what is the force of gravity on me?
Using the earth’s mass of 6x1024kg and radius of 6.4x106m
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Newton’s Law of Gravity
If And What does at the earth’s surface
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Gravitational fields
Using Newton’s law, what happens to earth’s gravitational field as you move further away from it?
It gets smaller
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Gravitational Fields
A field is a series of arrows, which show the direction of a certain force
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Gravitational Fields
The arrows are the same distance apart and direction because…
Distance apart = strength of field At the earths surface gravity is the
same.
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Gravitational Fields
When we zoom back…
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Gravitational Fields
As we move out, the arrows are further apart = less gravity
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Gravitational Fields
Using and [Mass earth: 6x1024kg ;
Radius:6400km] At… 400km (ISS), g = … 36000km (comm sat), g = …
Something to think about …
8.7ms-2
0.22ms-2
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Gravitational Fields
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So how do satellites orbit the earth?
There is still gravity there… Newton’s thought experiment
[Draw on board]
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Satellites
So, satellites go around the earth, in circular motion
What force keeps them in motion? Gravity What equations can we remember from
circular motion?
Therefore,
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Satellites
What do we know about the force of gravity?
Equate the two
What cancels?
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Satellites
Whoop de doo basil – what does it all mean?
It doesn’t matter what the mass of the satellite is!
If this wasn’t the case it would be a wee problem… think space walks …
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Space walks…
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Kepler’s Law
In a circular motion,
So equation from last page becomes Working on the board
Or This is similar to , but we have the time
period instead of the velocity
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Satellites
Eg, sometimes you might want to know the time period of a satellite (how many hours it takes to go around the earth) and sometimes you want to know what the orbiting speed is.
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Geostationary Satellites
A geostationary satellite is one that has an orbiting period exactly equal to one day (24 hours in earth’s case)
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Example Questions
1) Calculate the orbiting radius of a geostationary orbit
2) Calculate the orbiting time of the ISS [400km height]
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Question 2012 Q8 a
Note… Tricky little question…
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Question Sample Q8a-c
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Questions
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Looking at Satellites
And iridium flares Who has seen a satellite going across? http://www.heavens-above.com http://spotthestation.nasa.gov/
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Energy changes in gravity fields
Graphs
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Apparent weight and weightlessness
ISS orbits at 400km (g=8.7ms-2) But …
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How can they be weightless?
If a space ship travelled into deep space, where g=0ms-2 , then the astronauts would be truly weightless
Astronauts in “near earth” orbits “appear weightless”
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When else do you feel reduced weight or weightlessness?
Getting to the top of a lift Starting the lift (going down) Driving over the top of a small hill Falling
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Apparent Weight
Our apparent weight is equal to the normal force acting on us
At the bottom of a roller coaster we feel heavy (large normal force)
At the top we feel light (low normal force)
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Vomit Comet…
Video
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Apparent Weightlessness
When a space shuttle is orbiting the earth, the force of gravity is = to the centripetal force
There is no normal force! Astronauts are basically in a continual
free fall around the earth Therefore appear to be weightless! But why don’t they crash into earth? They are moving sideways as well
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Apparent Weightlessness
Its like the astronauts are at the top of a roller coaster loop-to-loop, with a slow enough force that they feel weightless. But their entire orbit around the earth feels like this!
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Questions
Sample Q 4 a-c 2012 Q8, b
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Kerbal Space Program
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Kerbal Space Program
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Revised Concept Map
Make a concept map with Forces in the middle.
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Use concept map to predict what type of questions are being asked
And do some questions for revision…
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Some questions (from exams)
Finish remaining questions from Sample, 2012, and 2011 in the “Motion” section
2012: Q1a-d, 6a-b, 7a-c 2011: 1,2,3, 21-23
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Electronics and Photonics
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Topics
Review of electronics Voltage dividers and thermistors Diodes Amplification Photonics systems and modulation
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Electronics Review
Symbols Voltage Current Resistance Ohms Law Power Series Parallel
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Electrical SymbolsDevice Symbol Device Symbol
Wires crossed (not joined)
Cell
Wires joined Battery of cells
Resistor or other load
AC supply
Resistor Ammeter
Filament Lamp Voltmeter
Diode DC Supply
Earth or ground
Switch
CVCV
A
V
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Voltage
The amount of energy supplied by the battery per coulomb.
It is effectively “used up” by components of a circuit
Measured in Volts A voltmeter must be in parallel with a
component Also called “potential difference”
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Current
How many coulombs per second. Total current depends on the components
of the circuit: They “draw” current out of the battery
Measured in Amps Ammeter must be in series Current flows from + to – in a circuit. Or
from high voltage to low voltage (although the electrons flow the opposite way)
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Prac:
Revision of Electronics 1
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Resistance
All electrical components have a resistance
for an Ohmic resistor
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Ohm’s Law
An Ohmic resistor has constant resistance over it when different voltages are applied over it
Has a straight line graph for V-I
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Power
P=VI Can be calculated for each electrical
component (power used) Or calculated for battery (power
supplied) Measured in Watts (W)
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Series Circuits
This is an example of light bulbs in series…
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Series
In a series part of the circuit… Current doesn’t change Voltage is used up
eg
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Series
Eg, Find the total resistance of these bulbs
100Ω 100Ω 100Ω
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Series
Find the total resistance of these sets of bulbs
100Ω 50Ω 30Ω
20Ω 50Ω 30Ω
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Parallel Circuits
This is an example of bulbs in parallel…
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Parallel
In a parallel part of the circuit… Current splits up (but not necessarily in
half) Voltage is the same in each arm of the
parallel
eg
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Parallel
Find the total resistance
6Ω
3Ω
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Parallel
Find the total resistance
6Ω
1Ω
12Ω
12Ω
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Combining Series and Parallel…
Eg
4Ω
4Ω
4Ω
4Ω 4Ω
4Ω
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Prac
Revision Prac. Similar to the question in sample. Set up, which bulb is the brightest for
maybe three different circuits
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Combining series and parallel
Sample Q9a-c [Together] 2012 A2 Q1 2011 A2 Q1-4
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Voltage Dividers
In the following circuit, what would the voltage be, measured over…
Bulb A Bulb B?
100Ω
12V
100Ω
A B
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Voltage Dividers
Yes, in a series circuit, the voltage is divided between the components
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Voltage Dividers
What about in the following circuit. What is the voltage over
Bulb A Bulb B
100Ω
12V
50Ω
A B
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Voltage Dividers
What about now? Bulb A Bulb B
100Ω
12V
300Ω
A B
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Voltage Dividers
An now… Bulb A Bulb B
100Ω
12V
40Ω
A B
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Voltage Divider Prac
Make a voltage divider Make one with a variable resistor
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Voltage Dividers
What is a general rule for how the voltage is divided in a series circuit?
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Voltage Dividers
What are they good for? Demo: Variable resistor Room in the book to draw the circuit
diagram.
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Voltage Divider
If we swap the variable resistor from before with a thermistor or LDR, we can get a cool “control circuit”
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Voltage Divider
Thermistor: Is a resistor, whose resistance changes depending on its temperature
Symbol: Graph (Board)
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Voltage Divider
LDR: Light Dependant Resistor. A resistor whose resistance depends on
the amount of light falling on it. Symbol:
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Voltage Divider
Using a thermistor (or LDR), we can make a control circuit to control a fan (or air conditioner):
Circuit diagram When the temperature rises, the
resistance of the thermistor decreases.
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Voltage Divider
When the temperature rises, the resistance of the thermistor decreases.
The voltage increases in the output. When the voltage in the output reads a
certain amount, the fan circuit will turn on!
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Voltage Divider Questions
Samp. Q 13 2011 – A2 – Q 5 & 6
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Diodes
Quick Prac – Diodes. Increase voltage. Reverse Bias. Make graph
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Diodes
Diodes are a non-ohmic device They only allow current to flow in one
direction. This is called “forward bias” A diode connect in “reverse bias” will
allow no current to flow Diode symbol:
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Diodes
Threshold Voltage. After a diode reaches its threshold voltage, it conducts like a wire: resistance free
Note: You cannot connect a diode to a circuit without a resistor! It will short circuit and explode…
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Diode Graph
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Example Questions
Consider the following circuit. The diode has a threshold voltage of 3V.
12V
90ΩA
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Example
1. Will the bulb glow??2. How could you make it glow?3. Assume the diode is now the correct
way around. 4. What is the voltage used by the diode?5. What is the voltage used by the bulb?6. What is the current measured at point
A?7. What is the power used by the bulb?
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Diodes
Different types of diodes include Light Emitting Diode (LED), and photo diode.
Both still have the same characteristics as a diode
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Question
Sample Q10 a-b 2012 A2 Q2
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Amplification
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Amplification
A typical electrical signal, that is transmitting sound, might look like this…
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Amplification
Draw what it might look like if it was amplified 2x…
This is known as the “gain”
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Amplification
Amplifiers can de-amplify. Amplifiers can be inverting as well.
Draw the signal if it was amplified with an inverting amplifier with gain of -5
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Amplification
A typical voltage in/ voltage out graph looks like …
The gain is the slope of the graph. What is the gain of this graph? Is it
inverting/non inverting?
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Amplification
What is the gain of this graph? Is it inverting/non inverting?
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Amplification
Clipping can occur, if you attempt to amplify a signal larger than the amplifier can supply
This is called saturation of the amplifier The saturation voltage is the largest
that the amplifier can output If the signal has structure, this can
result in a distortion of the signal (Draw on board)
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Amplification
Amplification achieved with a transistor
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Amplification
More readily done today with an IC (integrated circuit) that has many transistors/resistors and capacitors built into it
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Prac: Amplification
Demo / prac
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Prac:
I'm looking for an opamp similar to a 5532 that I can operate using a> single 9 volt battery for the power supply. I use 5532's for general> audio circuits but my datasheet recommends a minimum supply voltage of> 10 volts for this device.>> Anyone know of a good low voltage opamp for audio aplications? BTW, a> deviced that is second sourced would be nice.
It depends a bit on what you're trying to do. 9v is a bit of an awkwardvoltage because many of the newer opamps are designed for the 3v or 5v rangeand won't go up to 9v; the older ones, as you know, are often designed forat least +/-5v, that is, 10v single supply.
Don't fret too much about the rated supply voltage. You can actually getdecent audio performance out of even those ones rated for at least 10v, on a9v battery. It's one of those things where the manufacturer won't promiseit but hundreds of thousands of audio devices have proven it does work.
The TL062 is probably the most common opamp that I encounter for 9v audiowork. It has the advantage of very low supply current. It is, however,very noisy and has crappy frequency response - that's the tradeoff. Forbetter sound at the expense of more supply current, the TL072 is a goodopamp. The LM358 has also been widely used for 9v audio, although it doeshave some shortcomings.
Note that both the TL062 and TL072 have improved versions, the TLE2062 andTLE2072 respectively, with better specs. The TLE2072 uses 1.8mA perchannel, is rated for supply voltages as low as 4.5v (single supply!), andhas a 10MHz gain bandwidth. I've used it in a number of battery-poweredaudio applications with good success.
As GregS points out, the OPA2134 is a truly excellent opamp, and is ratedfor 5v single supply. It does consume 3 times the current of the TLE2072,though.
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Questions
Sample 11 a-b 2012 A2 Q4 2011 A2 Q11, 12
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Photonics
Photonics is the transfer of information or signals using light.
We have it because electrical wire could only transfer one phone call per wire
Fibre optics can transfer up to 1000 phone calls per fibre cable!
Plus, its cheaper! Electrical cables are made from copper. Fibre is made from glass (silica), which is made from sand.
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How might you use light to transfer information
Morse code? What would we need? Something to produce the light Something to direct the lights travel Something to receive the light and to
“translate it”
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A photonics system
Diagram
Has encoder/modulator Emitter Transfer medium Receiver Demodulator
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Emitters
LED (Light emitting diodes) Laser Diodes – These are LED’s with a
laser cavity.
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Receivers
LDR – Light dependant resistors Photodiodes – Light dependant diodes
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Prac
LDR prac
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Modulation
Why How Modulation and demodulation of the
carrier wave.
Draw
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Some sort of prac
La Trobe. (Find out specifics)