Question 1

When a current flows through an ionic liquid such as salty water,the moving charges are

Accepted Answer

A) only protons. 
B) only electrons. 
C) only negative ions. 
D) only positive ions. 
E) both positive and negative ions.

Question 2

Four unequal resistors are connected in a parallel with each other.Which one of the following statements is correct about this combination?

Accepted Answer

A) The equivalent resistance is less than that of the smallest resistor. 
B) The equivalent resistance is equal to the average of the four resistances. 
C) The equivalent resistance is midway between the largest and smallest resistance. 
D) The equivalent resistance is more than the largest resistance. 
E) None of the other choices is correct.

Question 3

A 6.0-Ω and a 12-Ω resistor are connected in parallel across an ideal 36-V battery.What power is dissipated by the 6.0-Ω resistor?

Accepted Answer

A) 220 W 
B) 48 W 
C) 490 W 
D) 24 W

Question 4

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

Accepted Answer

A) be four times as large. 
B) be two times as large. 
C) decrease to one-half the original power. 
D) decrease to one-fourth the original power.

Question 5

An electronic component with a 17-Ω resistor is rated for use at power levels not exceeding 
How much current can safely flow through the component?

Accepted Answer

A) 0.91 A 
B) 1.21 A 
C) 238 A 
D) 0.22 A

Question 6

For the graph shown in the figure,what physical quantity does the slope of the graph represent for a dc circuit?

Accepted Answer

A) 1/(current) 
B) resistance 
C) 1/(resistance) 
D) current 
E) resistivity

Question 7

If a quantity you calculated has units of 
What is that quantity?

Accepted Answer

A) potential 
B) resistivity 
C) resistance 
D) capacitance 
E) current

Question 8

A 2.0-μF capacitor that is initially uncharged is charged through a 50-kΩ resistor.How long does it take for the capacitor to reach 90% of its full charge?

Accepted Answer

A) 0.90 s 
B) 0.23 s 
C) 2.2 s 
D) 2.3 s

Question 9

If the power rating of a 400-Ω resistor is 0.800 W,what is the maximum voltage that can safely be connected across the resistor?

Accepted Answer

A) 110 V 
B) 17.9 V 
C) 170 V 
D) 1.80 V

Question 10

Two capacitors are connected as shown in the figure,with C1 = 4.0 µF and C2 = 7.0 µF.If a voltage source V = 90 V is applied across the combination,find the potential difference across C1.

Accepted Answer

A) 57 V 
B) 36 V 
C) 60 V 
D) 9.0 V

Question 11

The power rating of a 400-Ω resistor is 0.25 W.What is the maximum voltage you can safely connect across its ends?

Accepted Answer

A) 10 V 
B) 20 V 
C) 30 V 
D) 40 V 
E) 50 V

Question 12

Four resistors having resistances of 20 Ω,40 Ω,60 Ω,and 80 Ω are connected in series across an ideal dc voltage source.If the current through this circuit is 0.50 A,what is the voltage of the voltage source?

Accepted Answer

A) 20 V 
B) 40 V 
C) 60 V 
D) 80 V 
E) 100 V

Question 13

A multiloop circuit is shown in the figure.Find the current I2 if the batteries are ideal.(It is not necessary to solve the entire circuit. )

Accepted Answer

A) -3 A 
B) 3 A 
C) 7 A 
D) -7 A 
E) 0 A

Question 14

A wire of resistivity ρ must be replaced in a circuit by a wire of the same material but four times as long.If,however,the total resistance is to remain as before,the diameter of the new wire must

Accepted Answer

A) be the same as the original diameter. 
B) be one-half the original diameter. 
C) be one-fourth the original diameter. 
D) be two times the original diameter. 
E) be four times the original diameter.

Question 15

For the graph shown in the figure,what physical quantity does the slope of the graph represent for ohmic material?

Accepted Answer

A) power 
B) resistivity 
C) 1/(resistivity) 
D) resistance 
E) 1/(resistance)

Question 16

A resistance heater is rated at 1200 W when operating at 110 V dc.What current will it draw?

Accepted Answer

A) 0.090 A 
B) 1.0 A 
C) 11 A 
D) 12 A

Question 17

When current is flowing in an ordinary metal wire,the magnitude of the average velocity of the electrons is closest to

Accepted Answer

A) 10 m/s. 
B) the speed of light. 
C) 1 mm/s. 
D) 1 km/s. 
E) 1 m/s.

Question 18

Consider two copper wires of equal cross-sectional area.One wire has 3 times the length of the other.How do the resistances of these two wires compare?

Accepted Answer

A) Both wires have the same resistance. 
B) The longer wire has 1/3 the resistance of the shorter wire. 
C) The longer wire has 3 times the resistance of the shorter wire. 
D) The longer wire has 9 times times the resistance of the shorter wire. 
E) The longer wire has 27 times times the resistance of the shorter wire.

Question 19

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

Accepted Answer

A) increases. 
B) decreases. 
C) does not change. 
D) increases for a time and then starts to decrease.

Question 20

A 9.0-V battery costs $1.49 and will run a portable CD player for 6.0 hours before running down and needing to be replaced.If this battery supplies a current of 25 mA to the player,what is the cost of the energy provided by the battery in dollars per kWh?

Accepted Answer

A) $11/kWh 
B) $110/kWh 
C) $1100/kWh 
D) $11,000/kWh

Exam 21: Electric Current and Direct-Current Circuits