Chapter 22 Reading Quiz Current and Resistancephysics.gsu.edu/dhamala/Phys1112/Slides/Chapter22.pdf · Slide 22-26 3. A battery makes a circuit with a lightbulb as shown. Two compasses

• Current

• Conservation of current

• Batteries

• Resistance and resistivity

•

Chapter 22

Current and Resistance

Topics:

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

• Simple circuits

Sample question:

How can the measurement of an electric current passed through a person’s body allow a determination of the percentage body fat?How can the measurement of an electric current passed through a person’s body allow a determination of the percentage body fat?

Slide 22-1

Reading Quiz

1. The charge carriers in metals are

A. electrons

B. positrons

C. protons

D. a mix of protons and electrons


The charge carriers in metals are

D. a mix of protons and electrons

Slide 22-2

1. The charge carriers in metals are

A. electrons

Answer


The charge carriers in metals are

Slide 22-3

Reading Quiz

2. A battery is connected to a resistor. Increasing the resistance of

the resistor will

A. increase the current in the circuit.

B. decrease the current in the circuit.

C. not affect the current in the circuit.



A. increase the current in the circuit.


C. not affect the current in the circuit.

Slide 22-4

2. A battery is connected to a resistor. Increasing the resistance of the resistor will


Answer




Slide 22-5

Reading Quiz

3. A battery is connected to a resistor. As charge flows, the chemical energy of the battery is dissipated as

A. current

B. voltage

C. charge

D. thermal energy


3. A battery is connected to a resistor. As charge flows, the chemical energy of the battery is dissipated as

Slide 22-6

3. A battery is connected to a resistor. As charge flows, the

chemical energy of the battery is dissipated as

D. thermal energy

Answer


3. A battery is connected to a resistor. As charge flows, the

chemical energy of the battery is dissipated as

Slide 22-7

Properties of a Current

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 22-8

Definition of a Current


Conservation of Current


Rank the bulbs in the following circuit according to their brightness,

from brightest to dimmest.

The wires below carry currents as noted. Rate the currents


The wires below carry currents as noted. Rate the currents and IC:

A. IA

> IB

> IC

B. IB

> IA

> IC

C. IC

> IA

> IB

D. IA

> IC

> IB

E. IC

> IB

> IA

Rank the bulbs in the following circuit according to their brightness,

The wires below carry currents as noted. Rate the currents I , IThe wires below carry currents as noted. Rate the currents IA, IB

Slide 22-11

Batteries


The potential difference between the terminals of a battery, often called the terminal voltage, is the

battery’s emf.

∆Vbat

= = εW

chem

q____

Slide 22-12

q

Simple Circuits


The current is determined by the potential difference and the resistance of the wire:

I =∆V

chem

R_____

Slide 22-13

Resistivity


The resistance of a wire depends on its dimensions and the resistivity of its material:

Slide 22-14

Checking Understanding

A battery is connected to a wire, and makes a current in the wire.

i. Which of the following changes would increase the

current?

ii. Which would decrease the current?

iii. Which would cause no change?

A. Increasing the length of the wire

B. Keeping the wire the same length, but making it thicker


B. Keeping the wire the same length, but making it thicker

C. Using a battery with a higher rated voltage

D. Making the wire into a coil, but keeping its dimensions the same

E. Increasing the temperature of the wire

A battery is connected to a wire, and makes a current in the wire.

Which of the following changes would increase the

Which would decrease the current?

Which would cause no change?

Increasing the length of the wire

Keeping the wire the same length, but making it thickerKeeping the wire the same length, but making it thicker

Using a battery with a higher rated voltage

Making the wire into a coil, but keeping its dimensions the

Increasing the temperature of the wire

Slide 22-15

A battery is connected to a photoresistor. When light shines on this

resistor, it increases the number of charge carriers that are free to move in the resistor. Now, the roofalls on the photoresistor. How does this affect the current in the circuit?

A. The current increases.

B. The current decreases.

Measuring Light Intensity


B. The current decreases.C. The current is not affected.

A battery is connected to a photoresistor. When light shines on this

resistor, it increases the number of charge carriers that are free to oom lights are turned off, so less light

falls on the photoresistor. How does this affect the current in the

Slide 22-16

A battery is connected to a photoresistor. When light shines on this resistor, it increases the number of charge carriers that are free to move in the resistor. Now, the roofalls on the photoresistor. How does this affect the current in the circuit?


Answer



A battery is connected to a photoresistor. When light shines on this resistor, it increases the number of charge carriers that are free to

oom lights are turned off, so less light falls on the photoresistor. How does this affect the current in the

Slide 22-17

The resistivity of the body is a good measure of its overall composition. A measure of the resistance of the upper afat in a person’s body. Let’s model a pers8.0 cm and length 20 cm. We can modelthat the muscle, far, and nonconductive portions (the bone) form simple regions. This simple model actually works quite well. For a typical adult, the bone has a cross-sectional area of 1.0 cm2; to a good approximation, the balance of the arm is fatty tissue or muscle.

Measuring Body Fat


A. Assume that the arm has 30% fat athe arm?

B. Now, assume that the arm has only 10% muscle. What is the resistance now?

The measurement of the resistance of thmeasuring a current. Too much current ccan be dangerous. Suppose we wish to limit the current to 1.0 mA. For each of the above cases, what is the maximum voltage that could be employed?

The resistivity of the body is a good measure of its overall composition. A r arm is a good way to estimate the percent erson’s upper arm as a cylinder of diameter el the composition of the arm by assuming

that the muscle, far, and nonconductive portions (the bone) form simple regions. This simple model actually works quite well. For a typical adult, the bone has a

; to a good approximation, the balance of the arm

t and 70% muscle. What is the resistance of

Now, assume that the arm has only 10% muscle. What is the resistance

f the arm is made by applying a voltage and t can be uncomfortable and, as we will see,

can be dangerous. Suppose we wish to limit the current to 1.0 mA. For each of the above cases, what is the maximum voltage that could be employed?

Slide 22-18

Power in Circuits


A resistor is connected to a 3.0 V battery; the power dissipated in

the resistor is 1.0 W. The battery is now traded for a 6.0 V battery. The power dissipated by the resistor is nowA. 1.0 WB. 2.0 WC. 3.0 WD. 4.0 W

Checking Understanding


A resistor is connected to a 3.0 V battery; the power dissipated in

the resistor is 1.0 W. The battery is now traded for a 6.0 V battery. The power dissipated by the resistor is now

Slide 22-20

A resistor is connected to a 3.0 V battery; the power dissipated in the resistor is 1.0 W. The battery is now traded for a 6.0 V battery. The power dissipated by the resistor is now

D. 4.0 W

Answer


A resistor is connected to a 3.0 V battery; the power dissipated in the resistor is 1.0 W. The battery is now traded for a 6.0 V battery. The power dissipated by the resistor is now

Slide 22-21

1. An electric blanket has a wire that runs through the interior. A current causes energy to be dissipated in the wire, warming the blanket. A new, low-voltage electric blanket is rated to be used at 18 V. It dissipates a power of 82 W. What is the resistance of the wire that runs through the blanket?

2. For the electric blanket of the aof the wire increases, what hap

How does this affect the current in the wire? The dissipated

Electric Blankets


How does this affect the current in the wire? The dissipated power?

An electric blanket has a wire that runs through the interior. A current causes energy to be dissipated in the wire, warming the

voltage electric blanket is rated to be used at 18 V. It dissipates a power of 82 W. What is the resistance of the wire that runs through the blanket?

above example, as the temperature appens to the resistance of the wire?

How does this affect the current in the wire? The dissipated How does this affect the current in the wire? The dissipated

Slide 22-22

Additional Clicker Questions

1. A set of lightbulbs have different rated voltage and power, as

in the table below. Which one has the highest resistance?

Bulb Rated voltage

A 10 VB 8 VC 12 VD 6 V


D 6 V

E 3 V


A set of lightbulbs have different rated voltage and power, as


Rated voltage Rated power1 W1 W2 W2 W2 W

3 W

Slide 22-23

1. A set of lightbulbs have different rated voltage and power, as


Bulb Rated voltage

A 10 V

Answer


A set of lightbulbs have different rated voltage and power, as


Rated voltage Rated power1 W

Slide 22-24


2. A set of lightbulbs have different rated voltage and power, as in the table below. Which one has lowest resistance?

Bulb Rated voltage

A 10 VB 8 VC 12 V

D 6 V


D 6 VE 3 V


A set of lightbulbs have different rated voltage and power, as in the table below. Which one has lowest resistance?

Rated voltage Rated power1 W1 W2 W

2 W2 W3 W

Slide 22-25

2. A set of lightbulbs have different rated voltage and power, as in the table below. Which one has lowest resistance?

Bulb Rated voltage

Answer


E 3 V

A set of lightbulbs have different rated voltage and power, as in the table below. Which one has lowest resistance?

Rated voltage Rated power

3 W

Slide 22-26

3. A battery makes a circuit with a lightbulb as shown. Two

compasses are near the wires before and after the bulb in the

circuit. Which compass experiences a larger deflection?

A. Compass 1 experiences a larger deflection.

B. Compass 2 experiences a larger deflection.C. Both compasses experience the same deflection.



A battery makes a circuit with a lightbulb as shown. Two



Compass 1 experiences a larger deflection.

Compass 2 experiences a larger deflection.Both compasses experience the same deflection.


Slide 22-27

3. A battery makes a circuit with a lightbulb as shown. Two



C. Both compasses experience the same deflection.

Answer


A battery makes a circuit with a lightbulb as shown. Two



Both compasses experience the same deflection.

Slide 22-28

4. In Trial 1, a battery is connected to a single lightbulb and the brightness noted. Now, in Trialadded. How does the brightness of these two bulbs compare to the brightness of the single bulb in Trial 1?

A. The brightness is greater.

B. The brightness is the same.C. The brightness is less.



C. The brightness is less.

In Trial 1, a battery is connected to a single lightbulb and the ial 2, a second, identical, lightbulb is

added. How does the brightness of these two bulbs compare to the brightness of the single bulb in Trial 1?

The brightness is greater.

The brightness is the same.


Slide 22-29

4. In Trial 1, a battery is connected to a single lightbulb and the brightness noted. Now, in Trialadded. How does the brightness of these two bulbs compare to the brightness of the single bulb in Trial 1?


Answer



In Trial 1, a battery is connected to a single lightbulb and the ial 2, a second, identical, lightbulb is

added. How does the brightness of these two bulbs compare to the brightness of the single bulb in Trial 1?

Slide 22-30

Additional Examples

How much time does it take for 1.0 C to flow through each of the

following circuit elements?

A. A 60 W reading light connected to 120 V.B. A 60 W automobile headlamp connected to 12 V.


How much time does it take for 1.0 C to flow through each of the

A 60 W reading light connected to 120 V.A 60 W automobile headlamp connected to 12 V.

Slide 22-31

Documents

Chapter 22 Reading Quiz Current and Resistancephysics.gsu.edu/dhamala/Phys1112/Slides/Chapter22.pdf · Slide 22-26 3. A battery makes a circuit with a lightbulb as shown. Two compasses