Chapter 20 concept questions

Two circuits present the same resistance to the current. In one circuit the battery causing the flow of current has a voltage of 9.0V, and the current is 3.0A . In the other circuit the battery has a voltage of 1.5V. What is the current in this other circuit?

0.50A

How does the resistance of a copper wire change when both the length and diameter of the wire are doubled? (a)It decreases by a factor of two. (b)It increases by a factor of two. (c)It increases by a factor of four. (d)It decreases by a factor of four. (e)It does not change.

A

When an incandescent light bulb is turned on, a constant voltage is applied across the tungsten filament, which then becomes white hot. The temperature coefficient of resistivity for tungsten is a positive number. What happens to the power delivered to the bulb as the filament heats up? (a)It decreases. (b)It increases. (c)It remains constant.

A

You have three resistors, each of which has a resistance . By connecting all three together in various ways, which one or more of the following resistance values can you obtain? (a) 3R (b)3/2 R (c) R (d) 2/3R (e) 1/3 R

A, B, D, and E

The drawing shows a circuit containing three resistors and three batteries. In preparation for applying Kirchhoff's rules, the currents in each resistor have been drawn. For these currents, write down the equations that result from applying Kirchhoff's junction rule and loop rule. Apply the loop rule to loops ABCD and BEFC. (20.10)

ABCD: 3V + 7V BEFC 5=7

The drawing shows a circuit that includes a bimetallic strip (made from brass and steel; see Section 12.4) with a resistance heater wire wrapped around it. When the switch is initially closed, a current appears in the circuit because charges flow through the heater wire (which becomes hot), the strip itself, the contact point, and the light bulb. The bulb glows in response. As long as the switch remains closed, does the bulb 20.4 (a)continue to glow, (b)eventually turn off permanently, or (c)flash on and off?

C

In circuit A the battery that supplies energy has twice as much voltage as the battery in circuit B. However, the current in circuit A is only one-half the current in circuit B. Circuit A presents ________ the resistance to the current that circuit B does. (a)twice (b)one-half (c)the same (d)four times (e)one-fourth

D

The drawings show two different resistor-capacitor arrangements. The time constant for arrangement A is 0.20 s. What is the time constant for arrangement B? (20.13) (a)0.050 s (b)0.10 s (c)0.20 s (d)0.40 s (e)0.80 s

E

The power rating of a 1000-W heater specifies the power that the heater uses when it is connected to an ac voltage of 120V . What is the total power used by two of these heaters when they are connected in series with a single ac voltage of 120V ? (a) 4,000 (b) 3,000 (c) 2,000 (d)1,000 (e) 500

E

The power rating of a 1000-W heater specifies the power that the heater uses when it is connected to an ac voltage of 120V . What is the total power used by two of these heaters when they are connected in series with a single ac voltage of 120V ? (a) 4000W (b) 3000W (c) 2000W (d) 1000 W (e) 500 W

E

A car has two headlights, and their power is derived from the car's battery. The filament in one burns out, but the other headlight stays on. Are the headlights connected in series or in parallel?

In Parallel

You have four resistors, each of which has a resistance . It is possible to connect these four together so that the equivalent resistance of the combination is also R . How many ways can you do it? There is more than one way.

There are two ways. One is to form two groups of two parallel resistors and then connect the groups in series. The other is to form two groups of two series resistors and then connect the groups in parallel.

A resistor is connected between the terminals of a battery. This resistor is a wire, and the following five choices give possibilities for its length and radius in multiples of Lo and ro , respectively. For which one or more of the possibilities is the current in the resistor a minimum? (a) Lo and ro (b)1/2 Lo and 1/2 ro (c) 2 Lo and 2 Ro (d) 2 Lo and Ro (e) 8 Lo and 2 Ro

b, d, e

An ideal ammeter has ________ resistance, whereas an ideal voltmeter has ________ resistance. (a)zero, zero (b)infinite, infinite (c)zero, infinite (d)infinite, zero

C

A toaster is designed to operate with a voltage of 120 V, and a clothes dryer is designed to operate with a voltage of 140 V . Based solely on this information, which appliance uses more power? (a)The toaster (b)The dryer (c)Insufficient information is given for an answer.

C

Two identical light bulbs are connected to identical batteries in two different ways. In method A the bulbs are connected in parallel, and the parallel combination is connected between the one battery's terminals. In method B the bulbs are connected in series, and the series combination is connected between the other battery's terminals. What is the ratio of the power supplied by the battery in method A to the power supplied in method B? (a) 1/4 (b)4 (c)1/2 (d)2 (e)1

B

Two materials have different resistivities. Two wires of the same length are made, one from each of the materials. Is it possible for each wire to have the same resistance? (a)Yes, if the material with the greater resistivity is used for a thinner wire. (b)Yes, if the material with the greater resistivity is used for a thicker wire. (c)It is not possible.

B

What would happen to the current in a circuit if a voltmeter, inadvertently mistaken for an ammeter, were inserted into the circuit? The current would (a)increase markedly (b)decrease markedly (c)remain the same.

B