Deck 17: Electric Current and Resistance

Question 1

How might one connect four 10. volt batteries to create one equivalent battery having a potential of 20. volts?

Answer 1

Connect two in series and place that in parallel with two others in series.

Question 2

Why does a lamp burn out quicker if it is turned on and off many times, rather than one that is left burning?

Answer 2

The Tungsten filament has a positive temperature coefficient of resistance. Thus when it is first turned on, its current is excessive and the filament for an instant evaporates some of its surface, thereby becoming thinner.

Question 3

Why can a 25. watt fluorescent lamp produce as much illumination as a 100. watt incandescent lamp?

Answer 3

The incandescent lamp produces heat out of the majority of the input energy and only a minority fraction becomes light. The fluorescent lamp produces more light, less heat.

Question 4

My hair dryer is rated at 1500. watts and my television only uses 100. watts, so why do I pay more for electricity for my TV than for my hair dryer in a year?

Question 5

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

A) generator.
B) battery.
C) none of the given answers
D) transformer.

Question 6

A battery acquires and stores

A) energy.
B) charge.
C) energy, charge, & potential.
D) charge & potential but not energy.
E) potential.

Question 7

When charging a battery, the terminal voltage is ________ the battery emf.

A) equal to
B) less than
C) more than
D) zero, as is

Question 8

When discharging a battery, the terminal voltage is ________ the battery emf.

A) zero, as is
B) less than
C) equal to
D) more than

Question 9

Figure 17-1 is a symbol for which of the following?

A) fuse
B) battery
C) galvanometer
D) capacitor
E) resistor

Question 10

Figure 17-2 is a symbol for which of the following?

A) voltmeter
B) battery
C) switch
D) resistor
E) capacitor

Question 11

Figure 17-3 is the symbol for a

A) resistor.
B) ground.
C) switch.
D) capacitor.
E) fuse.

Question 12

Figure 17-4 is a symbol for which of the following?

A) battery
B) fuse
C) capacitor
D) resistor
E) ground

Question 13

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

A) twice the voltage, and the same current will flow through each.
B) zero volts.
C) twice the voltage, and different currents will flow through each.
D) the same voltage and the same current will flow through each.
E) the same voltage, and different currents will flow through each.

Question 14

One terminal of a battery is connected to a closed circuit, while the other terminal is left unconnected. Which of the following statements is true?

A) No current flows through the battery, and the potentials of different points in the circuit are different.
B) Current flows through the battery, and the potential of any point in the circuit is unchanged.
C) Current flows through the battery, and the potentials of different points in the circuit are different.
D) No current flows through the battery, and the potential of any point in the circuit is the same.

Question 15

The net direction in which electrons flow through a circuit is:

A) the direction of the conventional current.
B) opposite of the direction of the conventional current.

Question 16

A negative charge, if free, tries to move

A) from low potential to high potential.
B) toward infinity.
C) from high potential to low potential.
D) away from infinity.

Question 17

A Coulomb per second is the same as

A) a volt-second.
B) a watt.
C) a Coulomb.
D) a volt per second.
E) an ampere.

Question 18

Which of the following materials has the largest conductivity (at 20°C)?

A) platinum
B) copper
C) glass
D) silver
E) iron

Question 19

The resistance of an object is defined as

A) (voltage)/(current).
B) (length)(resistivity)(cross-sectional area).
C) (voltage)(current).
D) (current)/(voltage).
E) (length)/(resistivity)(cross-sectional area).

Question 20

Negative temperature coefficients of resistivity

A) exist in semiconductors.
B) exist in conductors.
C) do not exist.
D) exist in superconductors.

Question 21

A device that doesn't obey Ohm's law is a

A) light bulb.
B) tungsten wire.
C) copper wire.
D) silver bar.
E) resistor.

Question 22

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

A) The longer wire has twice the resistivity of the shorter wire.
B) Both wires have the same resistivity.
C) The shorter wire has twice the resistivity of the longer wire.
D) The longer wire has four times the resistivity of the shorter wire.

Question 23

A device obeying Ohm's law must have a resistance which

A) is zero.
B) is proportional to current.
C) is constant.
D) is proportional to voltage.

Question 24

A potential difference (V) is applied to the ends of an object causing a current (I) to flow through it. If the object obeys Ohm's law we can obtain the resistance by

A) dividing current by voltage.
B) calculating I² V.
C) multiplying current by voltage.
D) dividing voltage by current.

Question 25

Which of the graphs in Figure 17-5 indicates that a positive temperature coefficient is obeyed for the entire range shown?

A) graph a
B) graph b
C) graph c
D) graph d

Question 26

Which of the graphs in Figure 17-6 below indicates that the material is likely a semiconductor?

A) graph a
B) graph b
C) graph c
D) graph d

Question 27

Consider a current moving from left to right through a resistor. Which end of the resistor is at higher potential?

A) indeterminate, depends if current is charging a battery or discharging a battery
B) right
C) left

Question 28

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?

A) Both wires have the same resistance.
B) The shorter wire has twice the resistance of the longer wire.
C) The longer wire has twice the resistance of the shorter wire.
D) The longer wire has four times the resistance of the shorter wire.
E) The shorter wire has four times the resistance of the longer wire.

Question 29

What do you buy from the "power" company?

A) energy
B) voltage
C) power
D) current
E) potential

Question 30

Appliances in the USA are designed to work on 110-120 V, whereas appliances in Europe operate on 220-240 V. What would happen if you tried to use a European electric shaver in this country?

A) It would probably work as well as it does in Europe, since it is the current rating, not the voltage rating, that matters.
B) It would barely work (or maybe not work at all), since the voltage here is too low to push enough current through the device.
C) It would probably overheat and burn up before very long.
D) This question cannot be answered without knowing the frequency used in Europe and in the USA, since this is the parameter that matters most in any electrical device that operates on alternating current.
E) It would probably work as well as it does in Europe, since it is the power rating, not the voltage rating, that matters.

Question 31

In the graph shown in Figure 17-7, what physical quantity does the slope represent?

A) resistivity
B) current
C) energy
D) conductivity
E) resistance

Question 32

A coffee maker, which draws 13.5 A of current, has been left on for 10.0 min. What is the net number of electrons that have passed through the coffee maker?

Question 33

In an electroplating process, it is desired to deposit 40.0 mg of silver on a metal part by using a current of 2.00 A. How long must the current be allowed to run to deposit this much silver? (The silver ions are singly charged, and the atomic weight of silver is 108.)

Question 34

The diameter of no. 12 copper wire is 0.081 in. The maximum safe current it can carry (in order to prevent fire danger in building construction) is 20. A. At this current, what is the drift velocity of the electrons? (The number of electron carriers in one cubic centimeter of copper is 8.5 × 10²².)

Question 35

The temperature coefficient of resistivity of platinum is 3.9 × 10^-3/K°. If a platinum wire has a resistance of R at room temperature (23.°C) , to what temperature must it be heated in order to double its resistance to 2R?

Question 36

A heavy bus bar is 20. cm long and of rectangular cross-section, 1.0 cm × 2.0 cm. What is the voltage drop along its length when it carries 4000. A? (The resistivity of copper is 1.69 × 10^-8 $\Omega$ -m.)

Question 37

A 25. meter long wire, of diameter 0.30 mm, connected to 3.00 volts draws 0.499 A.
(a) What is the resistance of the wire?
(b) What is its resistivity?
(c) What is its conductivity?

Question 38

A Tungsten wire is 1.50 m long and has a diameter of 1.00 mm. At 20.° C a current of 50. mA flows through the wire. [P 5.6 × 10^-8 ·m; $\alpha$ = 0.0045(C°)^-1]
(a) Determine the potential across the wire.
(b) If the wire temperature increases by 100. C°, what potential is now required to produce a current of 50. mA?

Question 39

A battery is rated at 12. V and 160. A . h. How much charge does the battery store?

Question 40

The heating element in an electric drier operates on 240. V and generates heat at the rate of 2.00 kW. The heating element shorts out and, in repairing it, the owner shortens the Nichrome wire by 10%. (Assume the temperature is unchanged, although in reality, the resistivity of the wire will depend on its temperature.) What effect will the repair have on the power dissipated in the heating element?

Question 41

The monthly (30 days) electric bill included the cost of running a central air-conditioning unit for 2 hr/day at 5000. W, and a series connection of ten 60. W lightbulbs for 5 hr/day. How much did these items contribute to the cost of the monthly electric bill if electricity costs 8¢ per kW-h?

Question 42

A lamp uses a 150. W bulb. If it is used at 120. V, what current does it draw and what is its resistance?

Question 43

A motor that can do work at the rate of 2 hp has 60% efficiency. How much current does it draw from a 120. V line? (1 hp = 746 W)

Question 44

A 200. ? resistor is rated at 1/4 W.
(a) What is the maximum current it can draw?
(b) What is the maximum voltage that should be applied across it?

Question 45

A flashlight draws 0.133 A from a 3.0 volt battery pack. In 2.0 minutes:
(a) how much charge flows from the battery?
(b) how much energy was supplied by the battery?
(c) how many electrons passed any point in the circuit every second?

Question 46

A home appliance is rated at 250. watts ic connected to 120. V.
(a) What current does it draw?
(b) What is its resistance?
(c) How many kw-h does it use in one 24-hour day?

Question 47

How much charge must pass by a point in 20 s for the current to be 0.10 A?

A) 0.005 C
B) 200 C
C) 2.0 C
D) 50 C

Question 48

What is the voltage across a 5.0- $\Omega$ resistor if the current through it is 5.0 A?

A) 4.0 V
B) 25 V
C) 100 V
D) 1.0 V

Question 49

A 4000- $\Omega$ resistor is connected across 220 V. What current will flow?

A) 0.055 A
B) 5.5 A
C) 18 A
D) 1.8 A

Question 50

A light bulb operating at 110 V draws 1.40 A of current. What is its resistance?

A) 78.6
B) 154 11eea3e1_329c_30b8_97f4_59d6cdb111fa_TB9720_11
C) 12.711eea3e1_329c_30b8_97f4_59d6cdb111fa_TB9720_11
D) 109 11eea3e1_329c_30b8_97f4_59d6cdb111fa_TB9720_11

Question 51

A carbon resistor has a resistance of 18 at a temperature of 20°C. What is its resistance at a temperature of 120°C? (The temperature coefficient of resistivity for carbon is -5.0 × 10^-4 /C°.)

A) 18 11eea3e1_329c_30b8_97f4_59d6cdb111fa_TB9720_11
B) 1611eea3e1_329c_30b8_97f4_59d6cdb111fa_TB9720_11
C) 15 11eea3e1_329c_30b8_97f4_59d6cdb111fa_TB9720_11
D) 1711eea3e1_329c_30b8_97f4_59d6cdb111fa_TB9720_11

Question 52

A 5.5 meter long Aluminum wire has resistance of 0.40 m, P= 2.82 × 10^-8 11eea3e1_329c_30b8_97f4_59d6cdb111fa_TB9720_11 · m; $\alpha$ = 4.29 × 10^-3C^-1. Its conductivity is

A) 233. . m.
B) 2.5 × 10³ 11eea3e1_9524_0969_97f4_7b1899809f65_TB9720_11 . m.
C) 3.55 × 10⁷ 11eea3e1_9524_0969_97f4_7b1899809f65_TB9720_11^-1 m^-1 .
D) 2.5 × 10³ 11eea3e1_9524_0969_97f4_7b1899809f65_TB9720_11^-1 .
E) 2.33 × 10⁷ 11eea3e1_9524_0969_97f4_7b1899809f65_TB9720_11^-1 m^-1.

Question 53

A 2.0 meter long Aluminum wire (R = 0.44m P= 2.82 × 10^-8 11eea3e1_9524_0969_97f4_7b1899809f65_TB9720_11-m, $\alpha$ = 4.29 × 10^-3C^-1) is connected in series to an 8.0 meter long Tungsten wire (R = 0.20m P= 5.6 × 10^-8 11eea3e1_dfc9_619a_97f4_13087e0a6d77_TB9720_11-m, $\alpha$ = 4.5 × 10^-3C^-1). What is the resistance of the combination if the wire is heated to 150.° C? Assume the initial temperature for both wires is room temperature (20°C)

A) 0.78 m11eea3e1_dfc9_619a_97f4_13087e0a6d77_TB9720_11
B) 0.69 m11eea3e1_dfc9_619a_97f4_13087e0a6d77_TB9720_11
C) 0.88 m11eea3e1_dfc9_619a_97f4_13087e0a6d77_TB9720_11
D) 1.00 m11eea3e1_dfc9_619a_97f4_13087e0a6d77_TB9720_11
E) 0.64 m11eea3e1_dfc9_619a_97f4_13087e0a6d77_TB9720_11

Question 54

A copper wire of 1.0 cm² cross-sectional area would have to be how long to have a resistance of 1.0 ohm?

A) 5.9 Mm
B) 5.9 m
C) 5.9 × 10⁴ m
D) 5.9 × 10² m
E) 5.9 km

Question 55

A 120-m long copper wire (resistivity 1.68 × 10^-8 https://storage.examlex.com/TB9720/https://storage.examlex.com/TB9720/. m) has resistance 6.0 11eea3e1_dfc9_619a_97f4_13087e0a6d77_TB9720_11. What is the diameter of the wire?

A) 0.65 m
B) 0.65 mm
C) 0.065 mm
D) 0.65 cm

Question 56

A typical public utility (power company) supplies electricity at an approximate cost of

A) 10.¢/kW . h.
B) 1.¢/kW . h.
C) $10./kW . h.
D) $1./kW . h.
E) $100./kW .h.

Question 57

A typical battery (e.g., D-cell or AA-cell) supplies electricity at an approximate cost of

A) $1./kW. h.
B) 10.¢/kW . h.
C) $10./kW . h.
D) $100./kW . h.
E) 1.¢/kW. h.

Question 58

A 500-W device is connected to a 100-V power source. What current flows through this source?

A) 20.0 A
B) 1.60 × 10¹⁸ electrons/s
C) 200. mA
D) 5.00 A
E) 50,000 A

Question 59

A battery has an internal resistance of 2 https://storage.examlex.com/TB9720/https://storage.examlex.com/TB9720/https://storage.examlex.com/TB9720/https://storage.examlex.com/TB9720/https://storage.examlex.com/TB9720/. This battery delivers maximum power to a load resistor that has a value of

A) 8 11eea3e2_313c_361b_97f4_95efb13da7e5_TB9720_11.
B) 1 11eea3e2_313c_361b_97f4_95efb13da7e5_TB9720_11.
C) 2 11eea3e2_313c_361b_97f4_95efb13da7e5_TB9720_11.
D) 4 11eea3e2_313c_361b_97f4_95efb13da7e5_TB9720_11.
E) zero ohms.