Deck 6: Direct-Current Circuits

Question 1

When a 20-V emf is placed across two resistors in series, a current of 2.0 A is present in each of the resistors.When the same emf is placed across the same two resistors in parallel, the current through the emf is 10 A.What is the magnitude of the greater of the two resistances?

A)7.2 $\Omega$
B)7.6 $\Omega$
C)6.9 $\Omega$
D)8.0 $\Omega$
E)2.8 $\Omega$

Answer 1

7.2 $\Omega$

Question 2

Determine the magnitude and sense (direction) of the current in the 500- $\Omega$ resistor when I = 30 mA.

A)56 mA left to right
B)56 mA right to left
C)48 mA left to right
D)48 mA right to left
E)26 mA left to right

Answer 2

56 mA left to right

Question 3

At t = 0 the switch S is closed with the capacitor uncharged.If C = 50 $\mu$ F, $\varepsilon$ = 20 V, and R = 4.0 k $\Omega$ , what is the charge on the capacitor when I = 2.0 mA?

A)360 $\mu$ C
B)480 $\mu$ C
C)240 $\mu$ C
D)600 $\mu$ C
E)400 $\mu$ C

Answer 3

600 $\mu$ C

Question 4

At t = 0 the switch S is closed with the capacitor uncharged.If C = 40 $\mu$ F, $\varepsilon$ = 50 V, and R = 5.0 k $\Omega$ , how much energy is stored by the capacitor when I = 2.0 mA?

A)20 mJ
B)28 mJ
C)32 mJ
D)36 mJ
E)40 mJ

Question 5

In an RC circuit, how many time constants must elapse if an initially uncharged capacitor is to reach 80% of its final potential difference?

A)2.2
B)1.9
C)1.6
D)3.0
E)5.0

Question 6

What is the current in the 10- $\Omega$ resistor ?

A)0.60 A
B)3.0 A
C)1.2 A
D)2.4 A
E)0.30 A

Question 7

If Q = 400 $\mu$ C and the potential difference VA - VB =-V in the circuit segment shown below, what is the current in the resistor?

A)1.0 mA right to left
B)1.0 mA left to right
C)3.5 mA right to left
D)3.5 mA left to right
E)None of the above

Question 8

Determine the potential difference Va - Vb shown in the circuit below.

A)(-5.0 V)
B)+5.0 V
C)(-10 V)
D)+10 V
E)0 V

Question 9

How much heat is produced in the 10- $\Omega$ resistor in 5.0 s when $\varepsilon$ = 18 V?

A)72 J
B)32 J
C)50 J
D)18 J
E)90 J

Question 10

What is the current in the 15- $\Omega$ resistor when $\varepsilon$ = 9.0 V?

A)0.20 A
B)0.30 A
C)0.10 A
D)0.26 A
E)0.60 A

Question 11

If $\varepsilon$ 1 = 4.0 V, $\varepsilon$ 2 = 12.0 V, R1 = 4 $\Omega$ , R2 = 12 $\Omega$ , C = 3 $\mu$ F, Q = 18 $\mu$ C, and I = 2.5 A, what is the potential difference Va-Vb?

A)(-30 V)
B)30 V
C)5.0 V
D)(-5.0 V)
E)(-1.0 V)

Question 12

How long will it take a charged 80- $\mu$ F capacitor to lose 20% of its initial energy when it is allowed to discharge through a 45- $\Omega$ resistor?

A)0.92 ms
B)0.64 ms
C)0.40 ms
D)0.19 ms
E)0.80 ms

Question 13

What is the magnitude of the potential difference across the 20- $\Omega$ resistor?

A)3.2 V
B)7.8 V
C)11 V
D)5.0 V
E)8.6 V

Question 14

What is the potential difference VB - VA when the I = 1.5 A in the circuit segment below?

A)+22 V
B)(-22 V)
C)(-38 V)
D)+38 V
E)+2.0 V

Question 15

At what rate is thermal energy being generated in the 2R-resistor when $\varepsilon$ = 12 V and R = 3.0 $\Omega$ ?

A)12 W
B)24 W
C)6.0 W
D)3.0 W
E)1.5 W

Question 16

Determine the resistance R when I = 1.5 A.

A)40 $\Omega$
B)8.0 $\Omega$
C)85 $\Omega$
D)28 $\Omega$
E)32 $\Omega$

Question 17

A capacitor in a single-loop RC circuit is charged to 85% of its final potential difference in 2.4 s.What is the time constant for this circuit?

A)1.5 s
B)1.3 s
C)1.7 s
D)1.9 s
E)2.9 s

Question 18

Determine R when I = 0.20 A and $\varepsilon$ = 18 V.

A)50 $\Omega$
B)8.0 $\Omega$
C)10 $\Omega$
D)20 $\Omega$
E)30 $\Omega$

Question 19

If the current in the 4.0- $\Omega$ resistor is 1.4 A, what is the magnitude of the potential difference, VA -VB?

A)69 V
B)55 V
C)62 V
D)48 V
E)31 V

Question 20

What is the magnitude of the current in the 20- $\Omega$ resistor?

A)0.75 A
B)0.00 A
C)0.25 A
D)0.50 A
E)1.00 A

Question 21

The circuit below contains three 100-W light bulbs and a capacitor.The emf $\varepsilon$ = 110V.At the instant the switch S is closed, which light bulb is brightest?

A)A
B)B
C)C
D)A and B
E)All three are equally bright.

Question 22

The circuit below contains 4 100-W light bulbs.The emf is 110 V.Which light bulb(s) is(are) brightest?

A)A
B)B
C)C
D)D
E)C and D

Question 23

If R1 = 10 $\Omega$ , R2 = 15 $\Omega$ , R3 = 20 $\Omega$ , and I = 0.50 A, at what rate is heat being generated in these resistors?

A)29 W
B)16 W
C)22 W
D)11 W
E)1.1 W

Question 24

If R1 = 3.0 $\Omega$ , R2 = 6.0 $\Omega$ , R3 = 12 $\Omega$ , and I = 0.50 A, at what rate is heat being generated in R1?

A)20 W
B)17 W
C)12 W
D)31 W
E)6.0 W

Question 25

Which of the identical light bulb(s) is(are) brightest when the capacitor has half its maximum charge?

A)A
B)B
C)C
D)A and B
E)All three are equally bright.

Question 26

What is the equivalent resistance between points a and b when R = 30 $\Omega$ ?

A)27 $\Omega$
B)21 $\Omega$
C)24 $\Omega$
D)18 $\Omega$
E)7.5 $\Omega$

Question 27

The circuit below contains three 100-watt light bulbs.The emf $\varepsilon$ = 110 V.Which light bulb(s) is(are) the brightest?

A)A
B)B
C)C
D)B and C
E)All three are equally bright.

Question 28

The circuit below contains 3100-W light bulbs and a capacitor.The emf is 110 V.Which light bulb(s) is(are) brightest? (Assume the capacitor is fully charged.)

A)A
B)B
C)C
D)A and B
E)All three are equally bright.

Question 29

The capacitors are completely discharged in the circuit shown below. The two resistors have the same resistance R and the two capacitors have the same capacitance C.After the switch is closed, the current:

A)is greatest in C1.
B)is greatest in C2.
C)is greatest in R1.
D)is greatest in R2.
E)is the same in C1, C2, R1 and R2.

Question 30

In a loop in a closed circuit, the sum of the currents entering a junction equals the sum of the currents leaving a junction because:

A)the potential of the nearest battery is the potential at the junction.
B)there are no transformations of energy from one type to another in a circuit loop.
C)capacitors tend to maintain current through them at a constant value.
D)current is used up after it leaves a junction.
E)charge is neither created nor destroyed at a junction.

Question 31

A certain brand of hot dog cooker applies a potential difference (120 V) to opposite ends of the hot dog and cooks by means of the joule heat produced.If 60 kJ is needed to cook each hot dog, what current is needed to cook four hot dogs simultaneously in 3.0 min?

A)11 A
B)2.8 A
C)8.3 A
D)2.1 A
E)3.6 A

Question 32

When a capacitor is fully charged, the current through the capacitor in a direct-current circuit is:

A)zero.
B)at its maximum value.
C)equal to the current in a resistive circuit in parallel with the capacitor circuit.
D)greater than the current in a resistor that is farther from the battery than the capacitor.
E)zero if it is the only capacitor, but maximum if there is another capacitor in series with it.

Question 33

The circuit below contains three resistors, A, B, and C, which all have equal resistances.The emf $\varepsilon$ = 110V.Which resistor generates the most thermal energy after the switch is closed?

A)A
B)B
C)C
D)A and B
E)All three generate equal amounts of thermal energy.

Question 34

Which two circuits are exactly equivalent?

A)A and B
B)B and C
C)C and D
D)D and E
E)B and E

Question 35

The diagram shown represents a portion of a wire in a circuit.A current is flowing in the wire in the direction shown.Under the convention that it is positive charge that flows the electric field points in the direction of the current.How can the electric field change direction where the wire bends?

A)There is an excess of negative charge in the centre of the wire.
B)There is an excess of positive charge at the bottom end of the wire.
C)There is an excess of negative charge at the right end of the upper portion of the wire.
D)There is an accumulation of positive charge on the surface, particularly at the bend, such that the sum of electric fields gives the new electric field.
E)There is an accumulation of electrical potential as the current traverses the wire.The higher potential in the lower half is the source of the field.

Question 36

What is the equivalent resistance between points a and b when R = 13 $\Omega$ ?

A)29 $\Omega$
B)23 $\Omega$
C)26 $\Omega$
D)20 $\Omega$
E)4.6 $\Omega$

Question 37

The circuit below contains three 100-watt light bulbs and a capacitor.The emf $\varepsilon$ = 110V.The capacitor is fully charged.Which light bulb(s) is(are) dimmest?

A)A
B)B
C)C
D)A and B
E)All three are equally bright (or dim).

Question 38

What is the equivalent resistance between points A and B in the figure when R = 18 $\Omega$ ?

A)48 $\Omega$
B)64 $\Omega$
C)80 $\Omega$
D)96 $\Omega$
E)110 $\Omega$

Question 39

The circuit below contains three 100-W light bulbs.The emf $\varepsilon$ = 110 V.Which light bulb(s) is(are) brightest?

A)A
B)B
C)C
D)B and C
E)All three are equally bright.

Question 40

The circuit below contains 5 identical light bulbs.The emf is 110 V.Which light bulb(s) is(are) brightest?

A)A: The one closest to the positive terminal of the battery.
B)A and C: The bulbs closest to the positive terminal of the battery.
C)A and B: Because they are closest to the terminals of the battery.
D)C and D: Because they receive current from A and B and from E.
E)E: Because the potential difference across E is that of the battery.

Question 41

A battery has an internal resistance of 4.0 $\Omega$ .Which of the following load resistors would have the most power delivered to it when connected across the battery?

A)1.4 $\Omega$
B)2.0 $\Omega$
C)4.0 $\Omega$
D)8.0 $\Omega$
E)16 $\Omega$

Question 42

A circuit consists of 2N resistors, all of resistance R, connected as shown below.A potential difference V is applied to one end, and the other end is at ground potential.The equivalent resistance of the circuit is:

A)
B)R.
C)
D)NR.
E)2NR.

Question 43

A parallel circuit consists of a 100 V DC power source, a 100 $\Omega$ resistor, and a variable resistor of resistance R, which varies from 0 to 100 $\Omega$ .The current in the circuit is:

A)directly proportional to R.
B)inversely proportional to R.
C)directly proportional to (100 $\Omega$ + R).
D)inversely proportional to (100 $\Omega$ + R).
E)neither directly nor inversely proportional to R or to (100 $\Omega$ + R).

Question 44

The circuit below shows three resistors in series.R3 > R2 > R1.The resistors are all made of the same wire with the same diameter but have different lengths.Rank the magnitudes of the electric fields in the resistors from least to greatest.

A)E3 < E2 < E1.
B)E2 < E1 = E3.
C)E1 = E2 = E3.
D)E1 = E3 < E2.
E)E1 < E2 < E3.

Question 45

The circuit below shows three resistors in parallel.R3 > R2 > R1.The resistors are all made of the same wire with the same diameter but have different lengths.Rank the magnitudes of the electric fields in the resistors from least to greatest.

A)E3 < E2 < E1.
B)E2 < E1 = E3.
C)E1 = E2 = E3.
D)E1 = E3 < E2.
E)E1 < E2 < E3.

Question 46

What is the maximum number of 100-W light bulbs you can connect in parallel in a 120-V home circuit without tripping the 20-A circuit breaker?

Question 47

An initially uncharged 10- $\mu$ F capacitor is charged by a 10-V battery through a resistance R.The capacitor reaches a potential difference of 4 V in a period of 3 s after the charging began.Find the value of R.

Question 48

A series circuit consists of a 100 V DC power source, a 100 $\Omega$ resistor, and a variable resistor of resistance R, which varies from 0 to 100 $\Omega$ .The current in the circuit is:

A)directly proportional to R.
B)inversely proportional to R.
C)directly proportional to (100 $\Omega$ + R).
D)inversely proportional to (100 $\Omega$ + R).
E)neither directly nor inversely proportional to R or to (100 $\Omega$ + R).

Question 49

A 5000- $\Omega$ resistor and a 50- $\mu$ F capacitor are connected in series at t = 0 with a 6-V battery.The capacitor is initially uncharged.What is the current in the circuit at t = 0? At t = 0.5 s? What is the maximum charge stored on the capacitor?