Electricity and Why it Moves - The Clear Falls...

Name: _____________________

Period: _____________________

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Unit 9: 1

Electricity and Why it Moves

Charge

Protons are held

together in the

nucleus by the strong

nuclear force, the

strongest force in

nature, but electrons

can move.

–

–

– +

+ +

+ –

A neutral object

has an equal

amount of protons

and electrons.

– +

+ +

+ –

A positive object has

lost electrons, so it

has more protons

than electrons.

–

– +

+ +

+ – – –

–

– –

A negative object

has gained electrons,

so it has more electrons

than protons.

Electricity is moving electrons;

Protons can’t move. Electricity

+

––

––

+

Negative

Electrons

Positive

Protons

Objects can be positive, negative, or neutral.

The unit of charge is the coulomb (C).

Electric Force Any two charges feel a force between them. Electric force depends on the types of charges,

the distance between the charges, and the amounts of the two charges.

Likes repel

Two charged balloons repel

each other, so they must be

the same charge (negative).

Opposites attract

Positive hydrogen

atoms in water are

attracted to the nega-

tively charged balloon, causing the water

stream to bend slightly

toward the balloon.

– +

Attracting Force

+ +

Repelling Force + +

+ +

Less force

More force

Just like gravity, electric

force increases as dis-

tance decreases. Closer

charges: more force.

Electric force increases

if either of the charges

increases. More charge:

more force.

+ +

++ ++

Less force

More force

Electricity comes from elec-

trons moving between atoms.

Separating Charges

Ground Ground (the earth) can take or give an infinite number of electrons. Ground is electrically

neutral. Both positive and negative charges will neutralize when grounded.

– +

+ +

+ –

A positive object

will take electrons from ground.

To ground some-

thing you can often

touch it to a pipe.

Pipes are usually

connected to

ground somewhere

in the building.

Symbol for

ground

– – – – –

e’s

–

– +

+ +

+ – – –

–

– –

A negative object

will give electrons to ground.

– – – – –

e’s

Naturally, objects are neutral. Work must be done to separate charges. Separating charges

cause a charge difference and the electric force tries to move the charges back to neutral.

When two insulators rub, charges

move between them, causing a

separation of charge (static

electricity) and an electric force.

fur or hair

rubber rod

– –

– – –

– – –

–

Afterwards the rod is charged

and it can exert an electric force.

A big charge difference

can push thru big gaps,

like lightening arcing all

the way to the ground.

A Van de Graaff

generator pro-

duces a charge

difference.

arcing

– – –

– –

–

neutral

If there is a difference of charge electricity can move between

objects. A big enough difference can cause electricity to arc

(jump a gap). Bigger differences of charge allow bigger arcs.

No difference in charge—electricity can not move.

Batteries cause elec-

trons to move by

separating charges

in chemicals. When

connected by wires

the charge can flow,

eventually neutraliz-

ing the battery.

.

– +

Batteries

Name: _____________________

Period: _____________________


Unit 9: 1

1. Positive

2. Negative

3. Neutral

4. Coulombs

5. Electric force

6. Strong Nuclear

Force

A. A push or pull caused by charges.

B. The units for charge.

C. When an object has more protons than

electrons.

D. When an object has an equal number

of electrons and protons.

E. What keeps protons bound in the

nucleus of an atom.

F. When an object has more electrons

than protons.

1. Ground

2. Arcing

3. Charge

Difference

4. Van de Graff

5. Electricity

6.

A. The symbol for ground.

B. Moving electrons.

C. When a spark jumps between two objects.

D. Can accept or give an infinite amount of

electrons. Will neutralize charge.

E. A machine that separates charge.

F. Causes an electric force and charges to

move.

A balloon is rubbed against hair. Afterwards it sticks to a wall.

A) Is the balloon attracted or repelled by the wall?

B) Are the balloon and wall oppositely charged or like charged?

You walk across a carpet. When you try to touch a door knob a

spark jumps between you and the door knob. Why?

An object has a charge of 4.5 C.

A) Is the object positive or negative?

B) Did it gain or lose electrons?

C) If you touch it to ground, will it lose electrons to ground

or gain electrons from ground?

D) What will its charge be after it is grounded?

What Charge: Positive (+), Negative (–), or Neutral (0)?

____

____

___

–

–

– +

+ +

+ –

– +

+ +

+ –

–

– +

+ +

+ – – –

–

– –

___ 2 protons and 4 electrons

___ 18 protons and 16 electrons

___ A piece of rubber after rubbing

it with fur.

–8C

___ Two positive charges.

___ A positive and negative

charge.

___ Two balloons on a string

pushing apart.

___ A 3 C charge and a

–4C charge.

Attract or Repel?

Does the Electric Force increase or decrease?

_____ If the distance between the charges increases?

_____ If one of the charges is bigger (increases)?

_____ If both of the charges decrease (gets smaller)?

_____ If the charges get closer?

+ +

– +

– –

What are the charges of the second objects?

+ –

A negatively charged

rubber rod is brought close

to the metal top of an

electroscope.

A) Will the electrons in the

metal stay near the rod or

move away from the rod?

B) Why?

C) On the diagram, draw where

the electrons will go.

D) What will the metal leaves at

the bottom do?

Using the object at the right answer

the following questions.

A) Did it gain or lose electrons?

B) When grounded, will it gain or lose

electrons from ground?

C) Draw a wire grounding it.

D) What will its charge be after grounding?

Two objects are charged, but do not arc. Give two ways to make

them arc.

– – –

– – –

–

–

–

Electroscope

Metal

Rubber rod

leaves

Name: _____________________

Period: _____________________


Unit 9: 2

Circuits and Symbols

Electricity flows through circuits: paths of conductors (usually

wires). Any break in the circuit will cause the circuit to fail, just

like a break in a pipe lets water leak out of a water system.

A closed circuit has no break:

electricity can flow. An open circuit has a break some-

where: electricity cannot flow.

Electricity works a lot like

water. Often imagining how

water would work in an

circuit will tell you how

electricity will work as well.

Voltage Pushes Electrons Resistance Resists Current Flow Current Flows Through Circuits

The flow of electrons we call current,

which moves through closed circuits.

Devices in the circuit do work, which

slows down (restricts) current.

+ –

– – –

–

–

– –

– – – –

– – – – –

– – –

– – – – – – –

Circuit continues

The ends of a battery are oppo-

sitely charged. This creates a force,

pushing electrons through the circuit.

3 Quantities of a Circuit

Voltage is measured in Volts. Current is measured in Amps. Resistance is measured in Ohms.

These three quantities are linked in any circuit.

Change one of them and one or both of the others will change.

Circuit diagrams

battery capacitor

These components look similar, but are

very different and have different functions.

bat

tery

light bulb

switch

resistor

Electrical

Device Symbol Function

Water

Equivalents

wire paths for electric-

ity to flow. pipes

battery pushes electricity through circuit.

pump

light bulb lights up; resists

electricity. no

equivalent

switch turns electricity

on and off valve

resistor resists flow of

electricity. restriction

in a pipe

Electrical Symbols

+

–

Circuit diagrams are a short-cut method of drawing

circuits. They don’t need to be perfectly draw,

but they can be drawn wrong.

The diagram on the right is a faster way of

drawing the circuit on the left. (Notice the

direction of the battery, which is important)

A break in a circuit

is anywhere an

insulator is in the

way of electricity’s

flow. Paper, plas-

tic, or even an air

gap can keep elec-

trons from flowing. + +

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

Name: _____________________

Period: _____________________


Unit 9: 2

1. Open circuit

2. Closed circuit

3. Circuit

diagram

4. Voltage

5. Current

6. Resistance

A. Slows down the flow of electricity.

B. A short-hand way of drawing electrical circuits.

C. A circuit with a break in it; no electricity will flow.

D. Pushes electricity through a circuit.

E. Electricity can flow through this.

F. The flow of electricity through a circuit.

Which of the following are correct?

–

+

A.

–

+ C.

–

+

B.

+

–

D.

1. Wires

2. Battery

3. Resistor

4. Light bulb

5. Switch

A. Used to create radiant energy.

B. Pushes electricity through the circuit.

C. Can turn the electricity on and off.

D. Allows electricity to flow.

E. Slows down the flow of electricity.

Draw a circuit diagram (starting on the left) with a battery, a re-

sistor, a light bulb, and a switch. Make sure it is a closed circuit,

connected with wires.

B. ____________

C. ____________

A. ___________

E. ____________

D. ____________

Label the diagram:

In the Lab

A. Resistor

B. Battery

C. Switch

D. Wire

E. Light bulb

1. Valve

2. Pipes

3. No equivalent

4. Resists flow

5. Pump

Match the electrical component with the water component and diagram symbol

a.

e.

b.

c.

d.

+

–

Paper _________

A Penny_______

Paperclip ______

Glass _________

Plastic ________

Cloth _________

Wood ________

A Dime _______

Water_________

Salt Water _____

Sugar Water ___

Rubber________

1) Build the following circuit, being sure to connect all components (parts) with wires. Make sure it works.

2) Reverse the direction of the battery. Does the light still work?

3) Remove the switch. Touch the two wires between the light bulb and battery together to be sure the light still turns on.

4) Use these two wires as probes to test which of the following are conductors (C) or insulators (I).

What two parts of a light bulb must be touched to make the

light bulb light up?

When the light bulb lights up, is this a closed or open circuit?

What does this mean about the inside of the light bulb?

When the light bulb lights up, what types of energy are used

and created?

Using only a battery, two wires, and a light bulb (no holder),

make the light bulb light. Which of the following diagrams

will light up the light bulb?

+

–

A.

+

–

D.

–

+

C.

– +

B.

Name: _____________________

Period: _____________________


Unit 9: 3

Current, Voltage, and Resistance

Current

Resistance Resistance slows down electricity.

More resistance = less current.

Electricity is flowing electrons. The amount of electricity flowing is called current.

A lot of

current.

– – –

– – –

– – –

More current means

more water flowing

or more electricity

flowing (more

electrons moving).

Electrical current is

measured in Amps, which is coulombs/sec

(just like gallons per sec).

Voltage pushes electricity.

More voltage = more current.

I =

Current equals the voltage

divided by the resistance.

Resistance (in ohms [Ω])

V

R Current

(in amps [A])

Voltage (in volts [V])

Current is dependent on voltage and resistance.

Current can never change voltage or current, but both voltage and resistance can change current.

Ex. How much current does a 12 V

battery push through a 3 Ω resistor?

V = 12 v

R = 3 Ω

I = ?

I =

V

R =

12 v = 4A

3 Ω

Ohm’s Law

Ohm’s Law can tell us the current, voltage, or resistance if the other two of them are known.

– – – –

–

–

–

–

– –

–

Dams hold back water. Resistors hold

back electrons. Both reduce current.

A light bulb is brighter

when it has more

current going thru it.

A device that uses

more energy uses

more current. A

louder radio pulls

(uses) more amps.

Devices that use more energy, use more current.

More current Less current

Voltage

Water falls due to gravitational poten-

tial energy (Ep). Likewise, current

moves because of electrical potential

energy given to electrons by voltage.

There must be a change (difference)

of voltage for current to move.

Just as a waterwheel slows

down the falling water, resistors

use the electrical potential

energy to do work (something

useful) . Anything that uses

electricity has resistance: light

bulbs, speakers, etc. Regardless

of the amount of resistance,

all the voltage is always used

up in any circuit.

Batteries can add together,

(increasing voltage) or subtract

(canceling each other out) if they

are put in the circuit wrong.

+ +

0 volts total

Light is

off No

current

6V 6V

+

1.5V

1.5V

3 V

0 V

1.5 V

High voltage

Zero potential energy

No voltage (0 V)

Ad

din

g E

ner

gy

(Wo

rk)

Current

flows

1.5V

Usin

g E

nerg

y

High potential energy Voltage pumps electricity,

doing work to give potential

electric energy (Ep) to the

electrons. Batteries give

voltage. The resistors use

all of the electrical potential

energy. This is why the

voltage always equals 0 volts just before it reenters

the battery.

6V

6V

6V

6V

6V

With the same voltage (2 batteries), more resistance

(2 bulbs) = less current (dimmer bulbs).

With the same resistance (1 bulb), more voltage

(2 batteries) causes more current (brighter).

Increasing voltage increases current.

Increasing resistance decreases current.

Decreasing voltage decreases current.

Decreasing resistance increases current.

Very little

current.

– – –

Name: _____________________

Period: _____________________


Unit 9: 3

1. Voltage

2. Current

3. Resistance

4. Amps

5. Ohms (Ω)

6. Volts

A. Units for voltage.

B. Slows electricity down in a circuit.

C. Units for current.

D. Pushes electrons thru a circuit.

E. Units for Resistance.

F. Amount of electricity flowing in a circuit.

Which will have more resistance: an insulator or a conductor?

Which resistor is the better conductor: 150Ω or 600Ω?

Which resistor is the better insulator: 24Ω or 6Ω?

Which has more current flowing thru it?

A loud radio or a quiet radio?

A dim light bulb or a bright light bulb?

A fast toy car or a slow toy car?

A cold wire or a hot wire?

Which light bulbs will light? (All are in closed circuits.)

If it does light, draw an arrow to show the direction of current.

How much current does a 9V battery push thru a 3Ω resistor?

Variables Equation Solve

A 4 Ω resistor has 3A running thru it. Find the battery’s voltage.


An 18V battery produces 2A in the circuit. How much resistance

is in the circuit?


With the same resistance, which battery will cause more

current to flow: a 12V or a 24V battery?

Voltage give what kind of energy to electricity?

How much potential energy does water have after it falls to the

ground?

How much voltage does a circuit have just before going back

thru the batteries?

A) ____Flowing electrons.

B) ____Pushes electricity in

circuits.

C) ____Like a water pump.

D) ____Measured in Ohms.

E) ____Measured in Amps.

F) ____A battery gives this.

G) ____Measured in volts.

H) ___ Slows down current

in a circuit.

I) ___ Does work in an

electric circuit.

J) ___ Gives electric energy.

K) ___ 12 ohms

L) ___ 36 volts.

M) ___ 5 amps.

Voltage (V), Current (I), or Resistance (R)?

Voltage (V), Current (I), or Resistance (R)?

A _____ If you increase resistance what decreases?

B. ____ If you increases voltage what increases?

C. ____ If the current decreased what increased?

D. _____ If current increased what increased?

E. _____ If current increased what decreased?

F. _____ If resistance is decreased, what increases?

G. _____ More batteries will increase these two quantities.

A B C

D

E F G

H

High, Medium, or Low voltage?

Point A______

Point D______

Point F ______

Point C ______

Point E______

Point H _____

Point B______

Point G _____

Do batteries add or reduce voltage?

Do resistors add or reduce voltage?

A bird lands on a 20,000 volt wire. Both feet are touching.

A) What voltage is the bird’s left foot?

B) What voltage is the bird’s right foot?

C) What is the difference of voltage between the bird’s feet?

D) So, why can a bird land on an electrical wire and not get

electrocuted?

6 V

6 V

6 V

6 V

Total voltage

(VT) =

Total voltage

(VT) =

When the switch is closed

will the light turn on?

Why or why not?

Which of these

two water towers

would give the

most voltage to

a water circuit?

3V 3V 6V 3V 9V 0V 9V 9V

Name: _____________________

Period: _____________________


Unit 9: 4

Types of Circuits

Multiple Devices When you add batteries or resistors, it depends whether you add them in series or in parallel.

Because the have only one path:

objects in series have the same current.

Because both sides share wires with each other,

objects in parallel have the same voltage.

Resistors and batteries

in series add together.

Vtotal = 6 V

Batteries in parallel

share the same voltage

(they just last longer).

Resistors in parallel reduce total

resistance because there are more

paths for the current to flow.

4 Ω

4 Ω

Rtotal = 8 Ω Vtotal = 3 V

1.5 V

1.5 V

2A

2A

2A

2A

0 V

1.5 V

3 V 8 V

4 V

0 V

6 V 6 V

0 V

6 V

3Ω 2Ω

Rtotal = 1 Ω

6V

9 V

3 V

6V

The current is the same eve-

rywhere in a series circuit. The total current equals the sum

of the two branch currents.

Series vs. Parallel Circuits Series circuits have all only

one path for the electricity to flow.

There are no junctions.

Parallel circuits have multiple

paths for the electricity to flow.

If any part of a series circuit

is broken, the circuit fails.

The lights are dependent on

one another: if either light

is unscrewed both lights

will turn off.

The branches (paths)

of a parallel circuit are

independent: if one

light is unscrewed, the

other will stay on.

Your house is wired in parallel, so that each light and

appliance can be turned on and off independently.

Wires and Voltage

Junctions Just like in a river, current can split into

multiple paths or join from multiple paths.

Junction

Current splits

Current rejoins

Junction

Current can split

apart or join together.

Total current in an out

of a junction is equal.

12V

0V

12V

0V

12V

0V

12V

0 V

The voltage doesn’t change over a

wire, just over a battery or resistor.

Since wires are conductors,

they have no resistance,

so they have no

voltage difference.

The voltage change

over any wire is zero.

OR

The voltage is the

same everywhere

in the same wire.

Short Circuits A short-circuit (also called a “short”) is a wire that by-passes a device in a circuit.

Electricity always

chooses the path of

least resistance.

Since wires have

virtually no resistance,

electricity will go thru

a wire instead of a

device. This is known

as a short-circuit.

Both lights

stay off.

Short-circuit of battery Short-circuit This light turns off: it is “shorted”

out of the circuit.

When a device is short-circuited the

current by-passes it. It is easier for the

current to go thru the wire than the resistor.

Short-circuiting a battery not only drains the

battery, but could be dangerous. The wire

will heat up and the insulation could melt,

exposing the wire and possibly causing a fire!

4A

2A

6A

4A

2A

Junction

(current splits)

Junction

(current joins)

I1 I2

IT = I1 + I2

IT

IT

IT

IT

Name: _____________________

Period: _____________________


Unit 9: 4

1. Series

2. Short Circuit

3. Parallel

4. Branch

5. Junction

6. Zero

A. The voltage across any wire.

B. A circuit with multiple paths for current to flow.

C. Where current splits or joins.

D. An independent path for electricity in a parallel circuit.

E. When a wire by-passes a part of a circuit.

F. A circuit with only one path for the electricity.

Fill in the missing information on the following graphics.

___ Only one path for the electricity to flow.

___ Paths are dependent on each other.

___ How your house is wired.

___ Paths are independent of each other.

___ If one light turns off, the others stay on.

___ If you turn off one light, all the lights turn off.

___ Has more than one path for the electricity to flow.

___ Two devices have the same current.

___ Two devices have the same voltage.

Series or Parallel Circuit?

3 A 4 A

IT = _____

6 A I2 = _____

IT = 18 A

1. R1

2. VT

3. IT

4. V2

5. I2

6. RT

7. VAB

A. Voltage between A and B.

B. The total voltage in the circuit.

C. The resistance of resistor 1.

D. The current in branch 2 of the circuit.

E. Total current in the circuit.

F. The voltage of battery 2.

G. The total resistance of the circuit.

6 V 4 Ω 4 Ω

A

G

D

E

C B

F

6 V

3A 1A

IT = _____

I = _____

1A

Are these devices in Series or Parallel?

VT = _____ RT = _____ VT = _____ RT = _____

2V 2V

9V

9V

5Ω 4Ω

6Ω 6Ω

A. ______ B. ______ C. ______ D. ______

VT = ______ VAB = ______ VEA = ______

VFG = ______ VFB = _______ VCE = ______

VED = ______ VAC = _______ VDC = _______

A) What is the total voltage above?

B) What is the voltage from B to F?

C) What is the resistance from B to F?

D) Find the current flowing from B to F

(label it on the diagram).

E) How much current flows from C to G (label it)?

F) So, using D and E above, what is the total current

going thru point E (this is the total current [IT])?

G) Using VT and IT, find the total resistance of the circuit [RT].

Short-circuit the second bulb.

Draw the path the current will

follow with the short.

Which resistor will have

more current running thru

it?

Why?

Which light bulb will be brighter?

3 V

3 V

20 Ω 5 Ω

Name: _____________________

Period: _____________________


Unit 9: 5

The electrons that move

to make electricity come

mostly from the wires in

the circuit, not from the

battery. Metals are

conductors because their

electrons can move.

Power and Voltage Drops

Fuses

Electricity causes heat.

Fuses melt (or break)

when too much current

passes through it, protecting expensive electronic equip-

ment. Like fuses, circuit breakers protect against too

much current, also, but can be reset. instead of replaced.

Too much current causes the thin strip of metal to melt.

Fuse 2

5A

Electrons

– – – – –

–

–

– – –

–

–

– – – – –

–

– – – – –

–

–

–

+ –

1 electron out 1 electron in

1. Battery pushes out one electron

2. Electrons repel each other throughout the wire

3. One electron enters the

battery

Electrical Power Electrical power tells us how fast electricity is being used in a circuit or resistor.

A more powerful device uses the same amount of electricity, just faster.

Simplifying Parallel Circuits Finding the total current and power in a parallel circuit is much easier if you think of it

as two independent series circuits.

Voltage Drops Batteries add voltage; resistors use voltage. To find the voltage used by a particular resistor,

you have to know the current running thru it.

2. Use V = IR for each resistor. 1. Find the total current (IT).

4 Ω

2 Ω

Rtotal = 6 Ω Vtotal =24V

8 V

4A

244A

6

TT

T

VI

R= = =

8 V

8 V

Notice V = 8 V between the resistors. Also, the

total voltage used by the resistors must equal the

total voltage given by the batteries: 24 volts.

4A

4 Ω

2 Ω

16

V

8V

24 V

0 V

8 V

R1 uses 16 V,

leaving 8 V.

R2 uses 8 V,

leaving 0 V.

V1 = I1R1

= 4(4) = 16 V

V2 = I2R2

= 4(2) = 8 V

For objects in series the

biggest resistor uses the most

voltage and the most power.

Both light bulbs have the same

current, but the one with more

resistance is brighter because it uses

more voltage and uses more power.

24 V

PT = VTIT

PT = 24(4)

PT = 96 w

4 Ω

16 V

2 Ω

8 V

P1 = V1I1

P1 = 16(4)

P1 = 64 w

P2 = V2I2

P2 = 8(4)

P2 = 32 w

4 A

Power (in watts)

Voltage (in volts)

Current (in amps)

Electrical Power:

P = VI

Electrical Power equals

the voltage times the current.

V = 12 v

I = 3 A

P = ____

P = VI =

P = 12(3) = 36 w

Ex. A 12 V battery pushes 3 A

thru a light bulb. How much

power does the light bulb use?

100

W 40

W

A brighter bulb uses more power. Since

P= VI, a bulb could be brighter because it uses

more voltage with the same current OR because it

uses more current with the same voltage.

= +

Simplified

IT = 2 + 4 = 6A

Vtotal = 12V R2 = 3 Ω

22

2

124A

3

VI

R= = =

Semi-complicated

Remember that devices

in parallel have the

same voltage, but they

have different current.

6V

6Ω

Vtotal = 12V R1 = 6 Ω

11

1

122A

6

VI

R= = =

6V 3Ω

Branch 2 Branch 1

2A

6V

6Ω

6V 4A

6V

3Ω

6V

Both light bulbs have the same

voltage, but the one with less

resistance is brighter because it has

more current and uses more power

(this is how your house works).

P2 = V2I2

= 12(4) = 48 w P1 = V1I1

= 12(2) = 24 w

6Ω

3Ω

2Α 4A

12V

For objects in parallel, the one

smallest resistor uses the most

current and the most power.

Name: _____________________

Period: _____________________


Unit 9: 5

1. Fuse

2. Circuit breaker

3. Wire

4. Branch

5. Power

6. Junction

A. An independent path in a parallel circuit.

B. A device that breaks to protect against excessive current. Must be replaced.

C. Where branches joint or split.

D. Protects against high current, but can be reset.

E. Where most of the electrons in a circuit come from.

F. The product of voltage and current.

35 amps of current goes through a 40 amp fuse. What happens?

25 amps of current goes through a 15 amp fuse. What happens?

The electricity in your house is 120 volts. How many amps does

a 60 watt light bulb use?

How much power is used by a 120 V circuit using 6 amps?

A 240 volt circuit (like your dryer) has 20 amps flowing through

it. How much power is it using?

Split the following parallel circuit into two independent series

circuits.

3 V

3 V

6 Ω 3 Ω

Find the current in each circuit.

Find the total current.

Find the total resistance.

Label the voltages at the letters.

1 Ω

1 Ω

1 Ω

1 V

1 V

1 V

A

D

B

C

V at A =

V at B =

V at C =

V at D =

V T = ________________

R T = ________________

I T = ________________

V over R1 = _____________

V over R2 = _____________

V over R3 = _____________

P2Ω = ___________________

P3Ω = ___________________

PT = ___________________

9 V

3 V

R2 = 2 Ω

R1 = 1 Ω

R3 = 3 Ω

Series or parallel?

Series or parallel?

VT = _______________

VBranches = ___________

I1 = ________________

I2 = ________________

IT = ________________

RT = _______________

P6Ω = ______________

P3Ω = ______________

PT = _______________

6 V

6 V

6 Ω 3 Ω R1 = R2 =

IT

I1 I2

B1 B2

Which resistor will use more

power?

VT = ________________

VBranches = ____________

I1 = _________________

I2 = _________________

I3 = _________________

IT = ________________

RT = ________________

PT = ________________

I1 I2

IT

12v

12v

12 Ω 8 Ω 8 Ω

R1 = R2 = R3 =

I3

Which resistor uses the most

power?

Which resistor uses the

most power?

Why?

Which is brighter: a 60 W or a 100 W bulb?

Which one uses more power?

A 4 Ω and a 10 Ω light bulb are in series. Which one is brighter?

Why?

A 4 Ω and a 10 Ω light bulb are in parallel. Which is brighter?

Why?

Name: _____________________

Period: _____________________


Unit 9:

Meters

Multimeters As the name suggests, a multimeter can act like a multitude of meters. It can be a voltmeter,

ammeter, or ohmmeter, but you have to know how to use them in a circuit.

Ohmmeters An ohmmeter measures resistance (ohms). Measure resistors outside of the circuit.

4Ω

Measure resistance

outside a circuit.

Ammeters An ammeter measures current (amps). An ammeter must be in series with the circuit on.

A

A

CAUTION! An ammeter

is a very delicate device.

Incorrect usage can badly

damage the ammeter.

Incorrect Correct

3 V

3 V

6 Ω

1A

To correctly hook up an ammeter,

break the circuit where you want

to read the current and place the

ammeter into the break.

In this diagram there is only one

ammeter. It has been moved to

different parts of the circuit.

1.5 V

1.5 V

1 Ω 3 Ω

A3

A2

A1

4Α4Α4Α4Α

3Α 3Α 3Α 3Α

1Α 1Α 1Α 1Α

Voltmeters A voltmeter measures voltage (volts). A voltmeter must be in parallel like an ohmmeter,

but with the circuit on.

A multimeter allows you to

diagnose troubleshoot)

circuits or broken equip-

ment quickly. Many people

throw out items that can

be easily fixed.

By moving the

dial you select

which meter it is.

16V

V

Ω A

Use the probes

to test the circuit.

Ohmmeter Ω

V Voltmeter

A Ammeter

Circuit

Symbols

for

Meters

If a wire or resistor is

broken (bad) the ohm-

meter will read infinite

resistance or error.

Test each part of a

circuit to find which

part is broken.

- -

Must have

a break

A voltmeter can measure a battery in the circuit or out of the

circuit, while a resistor has no voltage outside of a circuit.

A voltmeter needs the circuit on. A voltmeter can read

the voltage given by a battery or used by a resistor.

4V

closed switch

4 Ω

8V

2 Ω

V

Circuit

symbol

12V

12V A car battery

only provides

12V, but a lot

of amps.

0V AA, AAA, and D

cell batteries read

1.5 V when new.

After time the volt-

age drops some.

Batteries also read

lower when on.

drained

An ohmmeter can measure individual

resistors or multiple resistors.

Ω

4 Ω

2 Ω

6 Ω

2Ω

4 Ω

4 Ω

6

Name: _____________________

Period: _____________________


Unit 9:

1. Voltmeter

2. Multimeter

3. Probes

4. Ammeter

5. Ohmmeter

A. Used to measure current.

B. Used to measure voltage.

C. The parts of the meter that touches the metal of the circuit device.

D. A device that can measure voltage, current, or resistance.

E. Used to measure a resistor.

9 V

9 V

R2 = 2 Ω

R1 = 4 Ω

R3 = 6 Ω

Ohmmeter, Voltmeter, or Ammeter

___ Must be in series.

___ The circuit has to be off.

___ Must be in parallel with the device being measured.

___ Used to tell the amount of current in the circuit.

___ The circuit must be on.

___ Delicate. Can be damaged if hooked up wrong.

___ Can measure if a battery is worn out.

___ Can measure a resistor only in a circuit.

___ Can measure a resistor out of the circuit.

6 V

3 V

2 Ω

9 Ω

1 Ω 1

5

3 2

4

Identify the meters as

voltmeters or ammeters.

M1: ______

M2: ______

M3: ______

M4: ______

M5: ______

Figure out what each meter reads.

How do you hook up an ohmmeter?

How do you hook up a voltmeter?

How do you hook up an ammeter?

What is the resistance for a good wire?

What is the resistance for a broken wire?

Draw meters that will

measure the following:

M1: Total voltage

M2: Total current

M3: Voltage over R2

Figure out what each meter reads.

In Lab:

Measure the three resistors you are given:

R1 = _________; R2 = _________; R3 = _________.

Put the above resistors in series. RT = _________.

How does RT compare with the individual resistors?

Put the above resistors in parallel. RT = _________.

How does RT compare with the individual resistors?

Build the following circuit:

1.5V

R2 = ____

R1 = ____

R3 = ____

1.5V

0

B A

D E

F

VAB = ________

VBC = ________

VCD = ________

VDE = ________

VEF = ________

VEA = ________

0 C

1.5 V

1.5 V

R1 = G R2 =

F

D E

B C

A R1 = __________

R2 = __________

VFA = _________

VBE = _________

VCD = ________

VED = ________

WITH THE MULTIMETER OFF: set up your circuit to read

the current in the first branch (at B or E). Have the teacher

check your setup before you turn it on.

I1 = __________

I2 = __________

IT = __________

Using VT and IT, calculate RT.

Check it with your ohmmeter.

6

Name: _____________________

Period: _____________________


Unit 9:

Magnets

Magnet Basics A magnet is anything that can attract or repel another magnet.

Horseshoe magnet

2) You can’t separate

a N pole from a S pole

(you just make

smaller magnets).

Bar magnets

Likes repel Opposite attract

repel

Donut magnets

3) Magnets exert magnetic forces

of attraction and repulsion.

1) All magnets

have two

poles: a north

and a south.

attract

Aluminum Stee

l

4) Magnets only attract ferrous

metals: Iron, Cobalt, and

Nickel (steel is an alloy of

mostly Iron and Nickel).

Electromagnets An electromagnet is a magnet made by moving electricity.

Electromagnets are particularly

useful because they allow us

to create forces that we can turn

on and off at will.

A toaster holds the

toast down with an

electromagnet. When

the electricity turns

off, the electromagnet

releases the toast

Ways to strengthen

an electromagnet:

1) Add electricity

(more current thru

more batteries, etc).

2) Add more coils

(the easiest way

to add electricity).

3) Add a ferrous core,

especially iron,

which becomes a

temporary magnet.

How do Magnets Work? Permanent magnets do not lose there magnetism. Many of the electrons in a permanent magnet are spin-ning the same way and the all of the little electromag-nets add up. Lodestone and Magnetite are the only two natural permanent magnetic materials.

Temporary magnets become magnets only when near a permanent magnet. The spinning electrons line up together when a magnet is near, but will eventually fall back after the magnet leaves. Only ferrous materials can become temporary magnets. Often bumping them (like dropping) can cause the electrons to fall back quickly.

N

S

Generators and Motors Moving electricity creates magnetic fields. Moving magnets make electricity.

Because electricity and magnetism are linked we can make motors and generators.

Something turns the

generator (does work)

causing magnets to

move, which creates

electricity. Dams,

cars, and power plants

all produce electricity

in this way. Work in (air):

Electricity out.

Generators generate electricity. Motors use electricity.

Electricity causes

magnetic forces thru

electromagnets. The

electromagnets

cause the object to

turn (do work).

Electricity in: work

out (moving air).

Motor or Generator?

It could be either one,

depending on how it is used.

Any motor can create electric-

ity and any generator will turn

if electricity is applied.

An electromagnet does not have to

have a core: any loops of electricity

will make an electromagnet.

e-

N Moving or spinning electrons in atoms cause magnetism.

If electrons are paired and spinning

in opposite directions, the magnets cancel

each other out. When a substance is magnetic many of the electrons

are spinning in the same direction.

7

Name: _____________________

Period: _____________________


Unit 9:

1. Permanent

magnet

2. Temporary

magnet

3. Motor

4. Generator

5. Core

6. Electro-

magnet

A. Turns when electricity is turned on.

B. Becomes a magnet near a magnet, then

loses its magnetism when moved away.

C. Becomes a magnet when electricity

moves in wire coils.

D. Uses work to make electricity.

E. Does not lose its magnetism: lodestone

and magnetite are only natural types.

F. Center of the electromagnet coils.

Draw a simple electromagnet:

Name three ways you could increase

the strength of an electromagnet:

N

S If the three

magnets are

attracting

each other,

label N and

S on the

second

magnet.

___

___

___

___

If the two

magnets are

repelling each other,

label N and S

on the sec-

ond magnet.

N

S

___

___

As a magnet gets closer to another magnet, does the magnetic

force increase or decrease?

___

___

N

S

The diagram show magnetic levitation

(Maglev). The top bar magnet is sus-

pended (floating) above the bottom

magnet while in a graduated cylinder

to keep it from falling to the side.

1) Two keep the upper magnet levi-

tated, are they attracting or repel-

ling each other?

2) Label N and S on the upper

magnet.

What makes a magnet on the atomic level?

Motor, Generator, or Both?

_____

_____

Work Electricity

Electricity Work

_____ Creates electricity.

_____ Has loops of wire in it.

_____ Creates motion.

_____ Is turned by a force.

_____ Can make electricity.

_____Used in a hydroelectric

dam.

_____Used in open or close

windows in a car.

_____Turns when electricity

is applied to it.

True or false (and why):

“A magnet will pick up any piece of metal.”

1) Label the north and south poles of

the nail magnet.

2) Will the nail stay a magnet when

removed from the bar magnet?

3) Is the nail a temporary

or permanent magnet?

Attract or repel?

Which electromagnet is stronger?

A or B?

B or C?

C or D?

A or C?

A or D?

Which is the strongest of the four?

B. 9V A. 9V

9V C. 3V D.

Attract or repel?

7

Name: _____________________

Period: _____________________


Unit 9:

Electricity and Magnetism Review

1. Voltage

2. Resistance

3. Power

4. Charge

5. Current

A. 8 amps

B. 8 volts

C. 8 coulombs

D. 8 watts

E. 8 ohms

1. Current

2. Voltage

3. Resistance

4. Insulator

5. Conductor

6. Circuit

A. A path for electricity to flow.

B. A material that allows electricity to

flow.

C. A material that resists electricity.

D. Slows down electricity

E. What pushes electricity in a circuit.

F. The flow of electrons thru wires. What moves: electrons or protons?

Why?

An object has a charge of –8 C.

A) Is the object positive or negative?

B) Did it gain or lose electrons?

C) If you touch it to ground, will it lose electrons to ground

or gain electrons from ground?

D) What will its charge be after it is grounded?

A _______________ allows electricity or heat to pass through it.

Electricity flows through paths called ___________. A

_________ circuit has no breaks in it, while an ___________

circuit has a break and stops the flow of electricity.

An ________________ will not allow electricity to pass.

Electricity is made up of flowing ______________.

Like electric charges attract/repel. Opposite charges attract/

repel.

What are the charges of the second objects?

+ – Attract Repel

What is electricity?

Why does electricity move?

What is arcing?

When and why does arcing occur?

-3C -3C

Will electrons flow between the two objects?

A. B.

5C 0C -2C -6C

Draw a circuit of two batteries, a light bulb, a resistor, and a

switch, all in series.

Increasing resistance _______ current

Decreasing resistance ______ current

Increasing voltage ______ current

Decreasing voltage ______ current

Increases (I)

Or

Decreases (D)

If a 12 v battery is connected to a 24 Ω resistor, how much current is flowing? How much voltage is needed to produce 2 amps through a 4 ohm light bulb? If a light bulb in your house (120 V) draws 0.5 amps, how much power does it use?

How can you tell if two light bulbs are in parallel?

How can you tell if two light bulbs are in series?

Is your house wired in series or in parallel?

Why?

You have two light bulbs and a battery in a circuit. If you add

another battery, do the light bulbs get brighter or dimmer?

Why?

You have two light bulbs and a battery in a circuit. If you add

another light bulb, do the light bulbs get brighter or dimmer?

Why?

8

Name: _____________________

Period: _____________________


Unit 9:

What is the change of voltage across a wire?

Why can a bird sit on a wire and not be electrocuted?

The three

magnets are

repelling each other.

Fill in the

missing

information.

N

___

___

___

___

___

The two

magnets are

attracting each other.

Fill in the

missing

information.

S

___

___

___

What will a magnet attract?

What will a magnet repel?

What does moving electricity cause?

What do moving magnets cause?

What is an electromagnet?

How do you strengthen an electromagnet?

What happens when you short circuit one light bulb in a two light

bulb circuit?

What happens if you short circuit a battery?

VT = ___________________ RT = ___________________ IT = ___________________ IR3 = ___________________ VR2 = ___________________ PT = ___________________

3 V

6 V

R2 =

5 Ω

R1 = 10 Ω

R3 = 3 Ω

Series or parallel?

Fill in the missing information on the following graphics.

2Ω

4Ω

RT = _____

3V

6V

VT = _____ IT = _____

5A 3A

VT = _________________

VDF = _________________

VHG = ________________

Vat F = ________________

I1 = ___________________

I2 = __________________

I3 = _________________

IT = __________________

RT = _________________

PT = _________________

Series

or

parallel? 6 V

6 V

R1 = 2 Ω

6 V

I1= I2= I3=

R3 = 1 Ω

R2 = 3 Ω

A

C B D

E G F H

Someone asks you how what a circuit is and how it works.

Tell them.

What is a motor?

How does it work?

What is a generator?

How does it work?

What are fuses and circuit breakers?

How are they different?

Where do most of the electrons come from that run thru a circuit?

8

Name: _____________________

Period: _____________________


Unit 9:

Purpose: To investigate how voltage and resistance affect the brightness of a light bulb in a circuit.

Background:

Students should know that a battery is a source of voltage. More batteries = more voltage

A light bulb causes resistance in a circuit. More light bulbs = more resistance

The brightness of the light bulb increases as the current through the light bulb increases.

Materials and Preparation: Have 2 batteries, 2 light bulbs, wires/alligator clamps or a spring board per set-up.

Electrical tape and Christmas lights offer an easy and inexpensive alternative to regular light bulbs.

Effect of changing voltage on light bulb brightness:

Effect of changing resistance on light bulb brightness:

Student Outcome-

Write a scientific statement to explain the effect of voltage and resistance on the brightness of a bulb.

Circuit # light bulbs # batteries relative brightness

1 1 1

2 1 2

3 1 3

Circuit # light bulbs # batteries relative brightness

1 1 2

2 2 2

3 3 2

Lab: How Bright is the Light? S1

Electricity and Why it Moves - The Clear Falls...

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