Electric Circuits ReviewElectric Circuits Review

Chapter 17 & 18Chapter 17 & 18

Electrical resistance in a wire depends on the wire’s

Electrical resistance in a wire depends on the wire’s

1. Resistivity

2. Length

3. Cross sectional area

4. All of the above

1. Resistivity

2. Length

3. Cross sectional area

4. All of the above

A metallic conductor has a resistivity of 18 x 106 m. What is the resistance of a piece that is 30 m long and

has a uniform cross sectional area of 3.0 x 106 m2?

A metallic conductor has a resistivity of 18 x 106 m. What is the resistance of a piece that is 30 m long and

has a uniform cross sectional area of 3.0 x 106 m2?

€

R = ρLA

= (18x10−6 )30

3.0x10−6=180Ω

A 0.20-m-long metal rod has a radius of 1.0 cm and a resistance of 3.2 x105 . What is

the resistivity of the metal?

A 0.20-m-long metal rod has a radius of 1.0 cm and a resistance of 3.2 x105 . What is

the resistivity of the metal?

€ R=ρLA3.2×10−5=ρ0.2π(0.01)2ρ=5.0×10−8Ωm

When two light bulbs are connected in series

When two light bulbs are connected in series

1. The same amount of current flows through each light bulb.

2. The current through each light bulb is proportional to the resistivity of the bulb.

3. The light bulbs will not work unless there is a fuse in the circuit.

4. There are at least two branches of the circuit.

1. The same amount of current flows through each light bulb.

2. The current through each light bulb is proportional to the resistivity of the bulb.

3. The light bulbs will not work unless there is a fuse in the circuit.

4. There are at least two branches of the circuit.

When one light bulb in a series circuit containing several light bulbs burns out…

When one light bulb in a series circuit containing several light bulbs burns out…

a. The other light bulbs burn more brightly

b. Nothing changes in the rest of the circuit

c. None of the other bulbs will light up

a. The other light bulbs burn more brightly

b. Nothing changes in the rest of the circuit

c. None of the other bulbs will light up

When resistors are put in series, their overall resistance is

When resistors are put in series, their overall resistance is

a. Larger than that of any individual resistor

b. The same as the resistance of one of the resistors

c. Smaller than the resistance of any of the resistors

a. Larger than that of any individual resistor

b. The same as the resistance of one of the resistors

c. Smaller than the resistance of any of the resistors

When resistors are put in parallel, their overall resistance is

When resistors are put in parallel, their overall resistance is

a. Larger than that of any individual resistor

b. The same as the resistance of one of the resistors

c. Smaller than the resistance of any of the resistors

a. Larger than that of any individual resistor

b. The same as the resistance of one of the resistors

c. Smaller than the resistance of any of the resistors

A wire 5.0 m long and 3.0 mm in diameter has a resistance of 100 . A 15 V potential

difference is applied across the wire. What is the current in the wire?

A wire 5.0 m long and 3.0 mm in diameter has a resistance of 100 . A 15 V potential

difference is applied across the wire. What is the current in the wire?

€

V = IR

I =VR

=15100

= 0.15A

Two appliances operate at the same voltage. Appliance A has a higher power

rating then appliance B. How does the resistance on A compare with that of B

Two appliances operate at the same voltage. Appliance A has a higher power

rating then appliance B. How does the resistance on A compare with that of B

1. A’s resistance is larger than B’s.2. A’s resistance is smaller than B’s3. A’s resistance is the same as B’s.

1. A’s resistance is larger than B’s.2. A’s resistance is smaller than B’s3. A’s resistance is the same as B’s.

€

P =V 2

R

What is the resistance of a 100. W light bulb if it is plugged into a 120. V outlet?What is the resistance of a 100. W light bulb if it is plugged into a 120. V outlet?

€

P =V 2

R

100 =1202

RR =144Ω

Three resistors with resistance of 6 , 12 , and 24 are connected in series. What

is the total resistance of the circuit?

Three resistors with resistance of 6 , 12 , and 24 are connected in series. What

is the total resistance of the circuit?

€

Rtotal

= 6 +12 +24 = 42Ω

Three resistors with resistance of 6.0 , 12 , and 24 are connected in series with a

12V battery. What is the current through the 12 resistor?

Three resistors with resistance of 6.0 , 12 , and 24 are connected in series with a

12V battery. What is the current through the 12 resistor?

€

V = IR

12 = 42I

I = 0.29A

The current is the same through all

of them so the total resistance must

be used.

What is the total resistance of this partial circuit?

What is the total resistance of this partial circuit?

12

6 6

6 12

6

€

Rtop

= 6+12 =18Ω

€

1Rtotal

=1

18+

16

=4

18

Rtotal

=184

= 4.5Ω

What is the current through each of the resistors in the following circuit?

(Rtotal = 4.5 )

What is the current through each of the resistors in the following circuit?

(Rtotal = 4.5 )

6 6

12 V 12

6 12 V / 6 = 2 A

6 12 V / 18 = 0.67 A

12 12 V / 18 = 0.67 A

What is the current in the 10- resistor?What is the current in the 10- resistor?

€

1Rparallel

=1

10+

16

+14

=6+10+15

60

Rparallel

=6031

=1.94Ω

Rtotal

=1.94 +2 = 3.94Ω

€

Itotal

=VRtotal

=12

3.94= 3.05A€

Vparallel

= IRparallel

Vparallel

= (3.05)(1.94)

Vparallel

= 5.91V

€

I10Ω

=Vparallel

R10Ω

I10Ω

=5.9110

= 0.59A

Which two resistors are in parallel with each other?

Which two resistors are in parallel with each other?

R2 and R3

Teams, place your bets

How much power is being dissipated by one of the 10 resistors?

How much power is being dissipated by one of the 10 resistors?

P = IV = V2/R = I2R

€

1Rparallel

=1

10+

110

+120

=5

20

Rparallel

= 4Ω

Rtotal

= 2 + 4 = 6Ω

€

Itotal

=VRtotal

=126

= 2A

€

Vparallel

= IRparallel

Vparallel

= (2)(4) = 8V

€

P10Ω

=Vparallel

2

R10Ω

=82

10= 6.4W