Electric Circuits Physics 11

A device that produces electricity by transforming chemical energy into electrical energy is called a

battery

A car battery

has an emf of 12 V consisting of six 2 V cells connected in series

The total amount of charge that passes through a wire’s full cross section at any point per unit of time is referred to as

current

The direction of conventional current is taken to be the direction that

positive charges would flow

A coulomb per second is the same as

an ampere

Car batteries are rated in “amp-hours.” This is a measure of their

charge

A current that is sinusoidal with respect to time is referred to as

a direct current

The resistance of a wire is defined as

V/I

What is 1 Ω equivalent to?

1 V/A

The resistance of a wire is

proportional to its length and inversely proportional to its cross-sectional area.

The resistivity of a wire depends on

the material out of which it is composed.

What conducting material has the lowest resistivity value?

silver

Consider two copper wires. One has twice the length of the other. How do the resistivities of these two wires compare?

Both wires have the same resistivity.

Consider two copper wires. One has twice the length of the other. How do the resistances of these two wires compare?

The longer wire has twice the resistance of the shorter wire.

Consider two copper wires. One has twice the cross-sectional area of the other. How do the resistances of these two wires compare?

The thicker wire has half the resistance of the shorter wire.

Consider two copper wires. One has twice the length and twice the cross-sectional area of the other. How do the resistances of these two wires compare?

Both wires have the same resistance.

The length of a wire is doubled and the radius is doubled. By what factor does the resistance change?

half as large

How much more resistance does a 1 18 .0 cm diameter rod have compared to a 2.0 cm diameter rod of the same length and made of the same material?

300%

The resistivity of most common metals

increases as the temperature increases.

Negative temperature coefficients of resistivity

exist in semiconductors.

Materials in which the resistivity becomes essentially zero at very low temperatures are referred to as

superconductors.

What is 1W equivalent to?

1 V·A

A kilowatt-hour is equivalent to

3 600 000 J.

If the resistance in a constant voltage circuit is doubled, the power dissipated by that circuit will

decrease to one-half its original value.

If the voltage across a circuit of constant resistance is doubled, the power dissipated by that circuit will

quadruple.

If the resistance in a circuit with constant current flowing is doubled, the power dissipated by that circuit will

double.

If the current flowing through a circuit of constant resistance is doubled, the power dissipated by that circuit will

quadruple.

During a power demand, the voltage output is reduced by 5.0%. By what percentage is the power on a resistor affected?

10% less

When two or more resistors are connected in series to a battery

all of the given answers.

When resistors are connected in series,

the current flowing in each is the same.

Three identical resistors are connected in series to a battery. If the current of 12 A flows from the battery, how much current flows through any one of the resistors?

12 A

Three identical resistors are connected in series to a 12 V battery. What is the voltage across any one of the resistors?

4 V

When two or more resistors are connected in parallel to a battery,

all of the given answers

When resistors are connected in parallel, we can be certain that

the potential difference across each is the same.

Three identical resistors are connected in parallel to a 12 V battery. What is the voltage of any one of the resistors?

12 V

Three identical resistors are connected in parallel to a battery. If the current of 12 A flows from the battery, how much current flows through any one of the resistors?

4 A

The potential difference between the terminals of a battery, when no current flows to an external circuit, is referred to as the

emf.

The potential difference between the terminals of a battery, when current flows to an external circuit, is referred to as the

terminal voltage.

You obtain a 100W light bulb and a 50W light bulb. Instead of connecting them in the normal way, you devise a circuit that places them in series across normal household voltage. Which statement is correct?

The 50W bulb glows more brightly than the 100W bulb.

As more resistors are added in series to a constant voltage source, the power supplied by the source

decreases.

As more resistors are added in parallel to a constant voltage source, the power supplied by the source

increases.

The lamps in a string of Christmas tree lights are connected in parallel. What happens if one lamp burns out? (Assume negligible resistance in the wires leading to the lamps.)

The brightness of the lamps will not change appreciably.

Consider three identical resistors, each of resistance 43 R. The maximum power each can dissipate is P. Two of

the resistors are connected in series, and a third is connected in parallel with these two. What is the maximum

power this network can dissipate?

3/2 P

State Kirchhoff’s junction rule.

Junction rule: the sum of all currents entering a junction equals the sum leaving it (conservation of charge).

State Kirchhoff’s loop rule.

Loop rule: the sum of all potential changes around any closed loop equals zero (conservation of energy).

Kirchhoff’s loop rule is an example of

conservation of energy.

Kirchhoff’s junction rule is an example of

conservation of charge.

Which of the equations here is valid for the circuit shown?

6 − I₂ − 2I₂ = 0

If you connect two identical storage batteries together in series (“+” to “ 49 −” to “+” to “−”), and place them in a circuit, the combination will provide

twice the voltage, and the same current will flow through each.

If you connect two identical storage batteries together in series (“+” to “ 50 −” to “−” to “+”), and place them in a circuit, the combination will provide

zero volts.

If you connect two identical storage batteries together in parallel, and place them in a circuit, the combination will provide

the same voltage and twice the total charge that one battery would.

An ideal ammeter should

introduce a very small series resistance into the circuit whose current is to be measured.

A galvanometer can be converted to an ammeter by the addition of a

small resistance in parallel.

A current reading is obtained by properly placing an ammeter in a circuit consisting of one resistor and one battery. As a result,

the current flowing in the circuit decreases.

Decreasing the resistance of an ammeter’s shunt resistance

allows it to measure a larger current at full scale deflection.

In order to construct a voltmeter from a galvanometer, one normally would

use a very large series resistor.

Increasing the resistance of a voltmeter’s series resistance

allows it to measure a larger voltage at full-scale deflection.

A voltage reading is obtained by placing a voltmeter across a resistor. What happens to the total current flowing in the circuit as a result of this action?

The current increases.

An unknown resistor is wired in series with an ammeter, and a voltmeter is placed in parallel across both the resistor and the ammeter. This network is then placed across a battery. If one computes the value of the resistance by dividing the voltmeter reading by the ammeter reading, the value obtained

is greater than the true resistance.

An unknown resistor is wired in series with an ammeter, and a voltmeter is placed in parallel across the resistor only. This network is then connected to a battery. If one computes the value of the resistance by dividing the voltmeter reading by the ammeter reading, the value obtained

is less than the true resistance.