Deck 27: Currents and Ohms Law

Question 1

In metric units, the dimensions of current are

A) coulombs.
B) coulombs·second.
C) coulombs/second.
D) coulombs·second².

Answer 1

coulombs/second.

Question 2

The direction of the conventional current flow is best described as

A) the direction of a hypothetical positive charge in the circuit.
B) the actual direction of the negatively charged electrons in the circuit.
C) the path the electrons follow from the positive to the negative terminals of the battery.
D) the path of ions from the positive to the negative terminals of the battery.

Answer 2

the direction of a hypothetical positive charge in the circuit.

Question 3

A current of 15 mA is passing through a wire. The time it will take for 15 C of charge to pass through a given point in the wire is

A) 1 ms.
B) 1.0 s.
C) 100 s.
D) 1000 s.

Answer 3

1000 s.

Question 4

A total of 3.0 $\times$ 10¹⁵ electrons pass through a wire in 48.0 ms. The current is

A) 10 $\mu$ A.
B) 0.10 mA.
C) 15 mA.
D) 100 pA.

Question 5

A 3.0-V potential is attached to a 1000- $\Omega$ resistor. The number of electrons that pass through the wire in one hour is

A) 7.7 $\times$
10¹⁹.
B) 6.7 $\times$
10¹⁹.
C) 5.7 $\times$
10¹⁹.
D) 4.7 $\times$

10¹⁹.

Question 6

The resistance of a wire is 1.2 $\Omega$ . The potential difference across the wire when 150 C pass through the wire in 15 seconds is

A) 1.2 V.
B) 12 V.
C) 120 V.
D) 120 mV.

Question 7

A current that is initially1.5 A decreases linearly to zero over 2.0 seconds. The total charge that passes through the wire is

A) 1.5 C.
B) 0.75 C.
C) 3.0 C.
D) 0 C.

Question 8

The electric field in a uniform wire is related to the potential across the wire, $\Delta$ V, and the length of the wire, $l$ , by

A) $\Delta$ V· $l$
B) $\Delta$ V/ $l$
C) $l$ / $\Delta$ V.
D) $l$ ²/ $\Delta$ V.

Question 9

The potential difference between two ends of a 45-cm length of wire is 1.5 V. The magnitude of the electric field in the wire is

A) 3.3mV/m.
B) 3.3 V/m.
C) 0.67 V/m.
D) 6.7 V/m.

Question 10

The potential difference between two ends of a 45-cm length of copper wire (1.7 $\times$
10^-8 $\Omega$ ·m) is 1.5 V. The magnitude of the current density in the wire is

A) 1.0 $\times$
10⁸ A/m².
B) 1.5 $\times$
10⁸ A/m².
C) 2.0 $\times$
10⁸ A/m².
D) 2.5 $\times$
10⁸ A/m².

Question 11

In metric units the dimensions of resistivity are

A) ohm.
B) ohm·second.
C) ohm·meter.
D) ohm/meter.

Question 12

The resistivity of a conductor depends on the collision time by an equation of the form

A) $\rho$ proportional tohttps://storage.examlex.com/TBN1003/11ef2d75_b9ef_d26b_a6da_330310546a56_TBN1003_11.
B) $\rho$ proportional to 11ef2d75_b9ef_d26b_a6da_330310546a56_TBN1003_11^-1.
C) $\rho$ proportional to 11ef2d75_b9ef_d26b_a6da_330310546a56_TBN1003_11^-2.
D) $\rho$ 0 proportional to 11ef2d75_b9ef_d26b_a6da_330310546a56_TBN1003_11².

Question 13

If the average collision time of an electron increases by a factor of 2, the resistivity of the material will

A) remain the same.
B) increase by a factor of 2.
C) decrease by a factor of 2.
D) increase by a factor of 4.

Question 14

A wire whose circular cross section is not uniform carries a current I. Relative to the larger region, the drift velocity in the narrower region is

A) larger.
B) smaller.
C) the same.

Question 15

A 2.0-m-long piece of wire has a diameter of 2.0 mm and a resistance of 0.018 $\Omega$ . The resistivity of the material is

A) $2.8 \times 10 ^ { - 8 } \Omega \cdot \mathrm { m } .$
B) $1.3 \times 10 ^ { - 7 } \Omega \cdot \mathrm { m } .$
C) $1.4 \times 10 ^ { - 8 } \Omega \mathrm { m } .$
D) $1.3 \times 10 ^ { 4 } \Omega \cdot \mathrm { m }$

Question 16

A current of 1.5 is produced through a conductor whose resistance is 0.50 $\Omega$ . The potential necessary to produce this current is

A) 3.0 V.
B) 0.75 V.
C) 0.33 V.
D) 1.1 V.

Question 17

A wire's diameter decreases linearly from d_i to d_f = d_i/2. If the wire has a current of I at the end whose diameter is d_i, then the current at the end whose diameter is d_i/2

A) decreases by a factor of 2.
B) increases by a factor of 2.
C) decreases by a factor of 4.
D) remains the same.

Question 18

A wire's diameter decreases linearly from d_i to d_f = d_i/2. If the electron drift velocity at the other end of the wire is v_i, then the drift velocity at the end whose diameter is d_i/2

A) decreases by a factor of 2.
B) increases by a factor of 2.
C) increases by a factor of 4.
D) remains the same.

Question 19

In metric units the dimensions of resistance are

A) volt.
B) volt·ampere.
C) ampere·volt.
D) volt/ampere.

Question 20

In metric units the dimensions of current density are consistent with

A) ampere.
B) ampere·meter.
C) ampere/meter².
D) ampere/meter³.

Question 21

The length of a wire is halved, and its radius is doubled. The resistance will change by a factor of

A) 4
B) 2
C) 1/2.
D) 1/4.
E) 1/8.

Question 22

Consider the resistance of two wires made of the same material. Wire A has a length that is twice the length of wire B; the cross-sectional area of wire A is twice the cross-sectional area of wire B. The resistance of wire A is

A) the same as wire B.
B) twice the value of wire B.
C) half the value of wire B.
D) one-quarter the value of wire B.

Question 23

A 75-m length of copper wire whose resistivity is 1.7 $\times$
10^-8 $\Omega$ . m has a resistance of 1.6 $\Omega$ . The diameter of the wire is

A) 0.50 mm.
B) 1.0 mm.
C) 1.5 mm.
D) 2.0 mm.

Question 24

The current through a copper wire (resistivity of 1.7 $\times$
10^-8 $\Omega$ .m that has a radius of 1.5 mm and length of 100.0 m when a 1.5-V potential is applied across the ends of the wire is

A) 0.16 A.
B) 0.62 A.
C) 6.2 A.
D) 1.6 A.

Question 25

A filament has a resistance of 0.10 $\Omega$ at 20°C. If the resistance becomes 0.14 $\Omega$ when the temperature of the filament increases to 90°C, the temperature coefficient of resistance for this material is

A) 5.7 *10^-3/°C.
B) 5.7 * 10^-4/°C.
C) 4.4 * 10^-3/°C.
D) 4.4 * 10^-4/°C.

Question 26

Negative temperature coefficients of resistivity

A) never occur.
B) occur in insulators.
C) occur in conductors.
D) occur in semiconductors.

Question 27

A resistor of 1000 $\Omega$ has 150 mA flowing through it. The voltage across the resistor is

A) 150 V.
B) 67 V.
C) 15 V.
D) 6.7 V.

Question 28

A hair dryer that draws 6.0 A when operating across a 110-V potential has a resistance of

A) 0.05 $\Omega$ .
B) 18 $\Omega$ .
C) 660 $\Omega$ .
D) 180 $\Omega$ .

Question 29

Two resistors are connected in series, and the value of R₁ is twice the value of R₂. The resistor with the larger potential across it is

A) R₁.
B) R₂.
C) neither; both resistors have the same potential across them.

Question 30

Two resistors are connected in series, and the value of R₁ is twice the value of R₂. The resistor with the larger current through it is

A) R₁.
B) R₂.
C) Both resistors have the same current through them.
D) None of the above answers is correct.

Question 31

Two resistors are connected in parallel, and the value of R₁ is twice the value of R₂. The resistor with the larger potential across it is

A) R₁.
B) R₂.
C) Both resistors have the same potential across them.
D) None of the above answers is correct.

Question 32

Two resistors are connected in parallel, and the value of R₁ is twice the value of R₂. The resistor with the larger current through it is

A) R₁.
B) R₂.
C) Both resistors have the same current through them.
D) None of the above answers is correct.

Question 33

A 10- $\Omega$ resistor is connected in series with a 30- $\Omega$ resistor. The total resistance of the combination is

A) 7.5 $\Omega$ .
B) 15 $\Omega$ .
C) 40 $\Omega$ .
D) 300 $\Omega$ .

Question 34

A 10- $\Omega$ resistor is connected in parallel with a 30- $\Omega$ resistor. The total resistance of the combination is

A) 7.5 $\Omega$
B) 15 $\Omega$ .
C) 40 $\Omega$ .
D) 300 $\Omega$

Question 35

A 10.0-V potential is applied across two resistors, R₁ and R₂, connected in series. If the potential difference across R₁ is 4.0 V, the value of R₂ is

A) 1/2 R₁.
B) 2/3 R₁.
C) 1.5 R₁.
D) 2 R₁.

Question 36

When a 1.5-V potential is applied across a parallel network of two identical resistors, the net current is 1.0 A. The individual resistance of each resistor is

A) 1.5 $\Omega$ .
B) 3.0 $\Omega$ .
C) 15 $\Omega$ .
D) 0.67 $\Omega$

Question 37

Five incandescent lightbulbs are connected in parallel. One of the bulbs burns out, causing the current through the other bulbs to

A) increase.
B) decrease.
C) remain the same.
D) drop to zero.

Question 38

Five incandescent lightbulbs are connected in series. One of the bulbs burns out, causing the current through the other bulbs to

A) increase.
B) decrease.
C) remain the same.
D) drop to zero.

Question 39

Two resistors, 20 $\Omega$ and 30 $\Omega$ , are connected in parallel. A third resistor, 24 $\Omega$ , is connected in series with the parallel combination. A 36-V power source is connected to the series-parallel combination. The current through the 24- $\Omega$ resistor is

A) 0.50 A.
B) 1.0 A.
C) 1.5 A.
D) 2.0 A.

Question 40

Two resistors, 20 $\Omega$ and 30 $\Omega$ , are connected in parallel. A third resistor, 24 $\Omega$ , is connected in series with the parallel combination. A 36-V power source is connected to the series-parallel combination. The current through the 20- $\Omega$ resistor is

A) 0.40 A.
B) 0.60 A.
C) 1.0 A.
D) zero.

Question 41

Two resistors, 20 $\Omega$ and 30 $\Omega$ , are connected in parallel. A third resistor, 24 $\Omega$ , is connected in series with the parallel combination. A 36-V power source is connected to the series-parallel combination. The current through the 30- $\Omega$ resistor is

A) 0.40 A.
B) 0.60 A.
C) 1.0 A.
D) zero.

Question 42

Two resistors, 20 $\Omega$ and 30 $\Omega$ , are connected in parallel. A third resistor, 24 $\Omega$ , is connected in series with the parallel combination. A 36-V power source is connected to the series-parallel combination. The voltage drop across the 20- $\Omega$ resistor is

A) 36 V.
B) 24 V.
C) 12 V.
D) zero.

Question 43

Two resistors, 20 $\Omega$ and 30 $\Omega$ , are connected in parallel. A third resistor, 24 $\Omega$ , is connected in series with the parallel combination. A 36-V power source is connected to the series-parallel combination. The voltage drop across the 24- $\Omega$ resistor is

A) 36 V.
B) 24 V.
C) 12 V.
D) zero.

Question 44

Two resistors, 20 $\Omega$ and 30 $\Omega$ , are connected in parallel. A third resistor, 24 $\Omega$ , is connected in series with the parallel combination. The equivalent resistance of the networks is

A) 16 $\Omega$
B) 36 $\Omega$ .
C) 50 $\Omega$ .
D) 74 $\Omega$ .

Question 45

Given a set of three identical resistors of equal value R, the following value cannot be generated from a combination of the complete set:

A) 3R
B) (1/3) R
C) (3/2) R
D) (2/3) R
E) Hold on; all of the above are possible.

Question 46

Four 24- $\Omega$ resistors are connected in a square configuration. The resistance as measured across any one of the resistors is

A) 12 $\Omega$
B) 18 $\Omega$ .
C) 24 $\Omega$ .
D) 96 $\Omega$ .

Question 47

The current in a wire is measured at 1.0 A when the wire is at 20.0°C. As the wire heats up to 80°C, the current drops to 0.77 A while the voltage remains constant. The temperature coefficient of resistance of the material is

A) 0.8 $\times$
10^-3 /°C.
B) 1.0 $\times$
10^-3 /°C.
C) 5.0 $\times$
10^-3 /°C.
D) 8.0 $\times$
10^-3 /°C.

Question 48

The current density of 1.5 $\times$
10⁵ A/m² is uniform across a wire whose radius is 4.0 mm. The current through the outer portion of the wire between the radii of 3.0 mm and 4.0 mm is

A) 1.1 A.
B) 2.2 A.
C) 3.3 A.
D) 4.4 A.

Question 49

A copper slab has dimensions of 20 cm x 30 cm x 60 cm. The two opposite sides of the slab that would have the largest resistance are given by the dimensions

A) 20 cm *30 cm.
B) 20 cm*60 cm.
C) 30 cm * 60 cm.
D) Hold on; all the resistances are the same.

Question 50

A 100- $\Omega$ resistor and a 200- $\Omega$ resistor are connected in series. These two are then connected in parallel to a 150- $\Omega$ resistor. The equivalent resistance of the set is

A) 50 $\Omega$ .
B) 100 $\Omega$ .
C) 200 $\Omega$ .
D) 450 $\Omega$ .