Electricity1 Electric and Magnetic Phenomena 5. Electric and magnetic phenomena are related and have...
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Transcript of Electricity1 Electric and Magnetic Phenomena 5. Electric and magnetic phenomena are related and have...
Electricity 2
1. Static electricity is a part of life. Can you name at least five examples of static electricity that occur in your home?
2. Fabric softeners are commonly used today because they eliminate static cling. Explain why clothes in the dryer get static cling.
Electricity 3
3. Why can walking across a carpeted room be a shocking experience?
4. Magnets have both north and south poles. While like poles repel each other, opposite poles attract each other. Explain the parallelism between magnetism and electric charge.
Electricity 5
Electric Charge
• Electrical property of matter
• Creates a force between objects
• Positive or Negative
Electricity 8
Electrical Charge
• Depends on the imbalance of electrons and protonso Protons = positiveo Electrons = negativeo Neutron = neutral
• Leads to a net charge
Electricity 10
Coulomb
• SI unit for charge
• Proton = +1.6 x 10-19 C
• Electron = -1.6 x 10-19C
• Charges are equal and opposite
Electricity 11
Flow of Charge
• Conductoro Material that
transfers charge easily
• Insulatoro Material that
does not transfers charge easily
Electricity 14
• Induces a positive charge near the rod• Induces a negative charge away from
the rod
Induced Charges
Electricity 17
Charging by Friction
• When rubbed together electrons can be transferred from one material to the other
• material that gets the electrons becomes negatively charged
• material that loses the electrons becomes positively charged
Electricity 18
Electric Force• The force of attraction or repulsion
between objects
• Due to charge
• Without electric force life would be impossible
• Depends on charge and distance
Electricity 19
Electric Force• Proportional to the product of
the charges
• Inversely proportional to the distance between them squared
• Equation: F = q1 q2 /[4o r2 ]
Electricity 21
Electric Field
•Produced around charged particles
•Other charged objects around will experience an electric force
•Electric force acts through electric fields
Electricity 23
Point Charges
• Electric field lines point in the direction of the electric force on a positive charge
Electricity 24
Point Charges
• Positive is attracted to negative
• Electric Field lines point inward
Electricity 25
Electric Field Lines
• Show direction of electric force
• Also show relative strength
Electricity 27
Electric Fields
Because the positive charge is twice as great as the negative charge.
In the figure shown, why do only half of the lines originating from the positive charge terminate on the negative charge?
Electricity 33
Electrical Potential Energy
• Potential energy of charged object
• Due to its position in electric field
Electricity 37
Potential Difference
• Change in the electrical potential energy per unit charge
• Measured in Joule / Coulomb
• 1 J/C = 1 volt or 1V or voltage
Electricity 38
Volts• Measure of potential
difference• Terminals of a battery have a
potential difference• Cell (battery)
o Source of currento Voltage across the terminals
Electricity 41
Current
• Voltage sets charges in motion
• Current = Rate of electric charges moving through a conductor1 C/s = 1 ampere or 1 amp
Electricity 42
Electric Current
• Produced when charges are accelerated by an electric field
• Charges move to a position of potential energy that is lower
Electricity 44
Electrical Resistance
• What is the voltage from the wall? o 120 V
• What is the power of a bulb?
40W, 60W, 100W
Electricity 46
Electrical Resistance
• Causes changes in current• Caused by internal friction• Slows the movement of charges through collisions• Collisions can cause material to
heat up
Electricity 47
Electrical Resistance(Ohm’s Law)
• Resistance = voltage/current
• R = V / I = V / A = Ohm
Electricity 48
Resistance
• A set of electric trains is powered by a 9 V battery. What is the resistance of the trains if they draw 3.0 A of current?
• Answer: 3
Electricity 49
Resistance
• A battery-operated CD player uses 12 V from the wall socket and draws a current of 2.5 A. Calculate the resistance of the CD player.
Electricity 50
Resistance
• There is a potential difference of 12 V across a resistor with 0.25 A of current in it. The resistance of the resistor is
• Answer: 48
Electricity 51
Ohms Law
• A light bulb has a resistance of 12 . It is attached to a battery that has a voltage of 24 V. Calculate the current in the light bulb.
• Answer: 2 A
Electricity 52
Current
• A resistor has a resistance of 280. How much current is in the resistor if there is a potential difference of 120 V across the resistor?
• Answer: 0.43 A
Electricity 65
Electric Energy
• Energy associated with electrical charges
• Whether moving or at rest
Electricity 66
Electrical Power
• Rate at which electrical energy is used in a circuit
• power = current x voltage
• P = IV
• 1 Watt = 1 Amp x 1 Volt
Electricity 67
• A color television draws about 2.5 A when it is connected to a 120 V outlet. Assuming electrical energy costs $0.060 per kWh, what is the cost of running the television for exactly 8 hours?
• Answer: $0.14
Electricity 68
8. • A flashlight bulb with a potential
difference of 4.5 V across its filament has a power output of 8.0 W. How much current is in the bulb filament?
• Answer: 1.8 A
Electricity 70
• 7. What is the potential difference across a resistor that dissipates 5.00 W of power and has a current of 5.0 A?
• Answer: 1.00 V
Electricity 71
11. • If a lamp is measured to have a
resistance of 120- when it operates at a power of 120 W, what is the potential difference across the lamp?
• Answer: 120 V
Electricity 72
12. • A microwave draws 5.0 A when it
is connected to a 120 V outlet. If electrical energy cost $0.090/kWh, what is the cost of running the microwave for exactly 6 hours?
• Answer: $0.32
Electricity 73
13.
• What happens to the overall resistance of a circuit when too many appliances are connected across a 120 V outlet?
• Answer: Resistance is decreased.
Electricity 74
11.
• An electric toaster has a power rating of 1100 W at 110 V. What is the resistance of the heating coil?
• Answer: 11
Electricity 75
13.
• A device that protects a circuit from current overload is called a(n)
• Answer: circuit breaker.
Electricity 77
16.
• A 180-ohm resistor has 0.10 A of current in it. What is the potential difference across the resistor?
• Answer: 18 V