Deck 19: Magnetism Magnets: Part A

Question 1

A copper cable needs to carry a current of 200 A with a power loss of only 1.5 W/m.What is the required radius of the copper cable? (The resistivity of copper is 1.7 × 10−⁸ Ω⋅m. )

A) 4.0 cm
B) 0.21 cm
C) 0.85 cm
D) 1.2 cm

Answer 1

1.2 cm

Question 2

A high voltage transmission line of diameter 2 cm and length 2 km carries a steady current of 1000 A.If the conductor is copper with a free charge density of 8 × 10²⁸ electrons/m³,how long does it take one electron to travel the full length of the cable? (e = 1.6 × 10−¹⁹ C)

A) 8 × 10² s
B) 8 × 10⁸ s
C) 8 × 10⁶ s
D) 8 × 10⁴ s

Answer 2

8 × 10⁶ s

Question 3

A wire carries a steady current of 0.1 A over a period of 200 s.What total charge passes through the wire in this time interval?

A) 2 C
B) 200 C
C) 0.005 C
D) 20 C

Answer 3

20 C

Question 4

How long is a wire made from 200 cm³ of copper if its resistance is 8.5 ohms? The resistivity of copper is 1.7 × 10^-5 Ω·m.

A) 10 m
B) 2.2 × 10² m
C) 7.1 m
D) 3.0 × 10³ m

Question 5

A 0.10-m long metal rod has a radius of 1.0 cm and a resistance of 3.2 × 10−⁵ Ω.What is the resistivity of the metal?

A) 5.0 × 10−⁸ Ω⋅m
B) 160 × 10−⁸ Ω⋅m
C) 10 × 10−⁸ Ω⋅m
D) 1.6 × 10−⁸ Ω⋅m

Question 6

If the current in a wire is halved,what effect does this have on the electron drift velocity in the wire?

A) It decreases by a factor of two.
B) It increases by a factor of four.
C) It stays the same.
D) It doubles.

Question 7

A lightbulb drawing a current of 0.60 A is run for 2.0 hours.How many electrons pass through the bulb during this process?

A) 2.7 × 10²²
B) 1.4 × 10¹⁹
C) 5.4 × 10²⁵
D) 4.3 × 10³

Question 8

A wire of length L is uniformly stretched to triple its original length.By what factor does its resistance change?

A) 1,i.e. ,no change
B) 3
C) 9
D)

Question 9

A Nichrome wire has a radius of 0.50 mm and a resistivity of 1.5 × 10−⁶ Ω⋅m.If the wire carries a current of 1.0 A,what is the potential difference per unit length along this wire?

A) 1.9 V/m
B) 0.95 V/m
C) 1.6 V/m
D) 0.003 V/m

Question 10

Three wires of the same diameter and length are made from three different metals: copper (ρ​ = 1.7 × 10^-8 Ω·m),aluminum (ρ​ = 2.7 × 10^-8 Ω·m),and silver (ρ​ = 1.6 × 10^-8 Ω·m).Which wire has the least resistance?

A) the aluminum wire
B) the silver wire
C) the copper wire
D) Since insufficient information is given to find the resistance of each wire,one cannot find the answer.

Question 11

A metallic conductor has a resistivity of 18 × 10−⁶ Ω⋅m.What is the resistance of a piece that is 15 m long and has a uniform cross sectional area of 6.0 × 10−⁶ m²?

A) 0.056 Ω
B) 45 Ω
C) 90 Ω
D) 160 Ω

Question 12

A 100-W light bulb is in a socket supplied with 120 V.What is the current in the bulb?

A) 7200 A
B) 0.83 A
C) 1.4 A
D) 0.50 A

Question 13

A length L of wire has a voltage V across its ends while a current I runs through the wire.If a voltage 3V were applied to another length of this same wire from the same coil and the same current were found to run through it,what is the length of this second wire?

A)

B)

C)

D)

Question 14

If a light bulb has half the resistance of a 50-W lightbulb,what would be its wattage? Assume both bulbs are attached to the same 120-V circuit.

A) More information is needed.
B) 25 W
C) 200 W
D) 100 W

Question 15

Wire A and Wire B are each carrying the same current.If the diameter of Wire A is half that of Wire B,how does the drift velocity v_dA in Wire A compare to that in Wire B?

A) v_dA = 4 v_dB
B) v_dA = 2 v_dB
C) v_dA = v_dB /2
D) v_dA = v_dB /4

Question 16

A 300-A·h battery can deliver how many coulombs starting from a full charge?

A) 4.8 × 10³
B) 4.3 × 10⁴
C) 7.2 × 10⁵
D) 1.1 × 10⁶

Question 17

If a metallic wire of cross-sectional area 3.0 × 10−⁶ m² carries a current of 9.1 A and has a mobile charge density of 4.24 × 10²⁸ carriers/m³,what is the average drift velocity of the mobile charge carriers? (charge value = 1.6 × 10−¹⁹ C)

A) 3.4 × 10³ m/s
B) 1.7 × 10³ m/s
C) 4.5 × 10−⁴ m/s
D) 1.5 × 10−⁴ m/s

Question 18

You measure a 20.0-V potential difference across a 5.00-Ω resistor.What is the current flowing through it?

A) 5.00 A
B) 4.00 A
C) 100 A
D) 1.00 A

Question 19

If a 9.0-V battery,with negligible internal resistance,and an 27-Ω resistor are connected in series,what is the amount of electrical energy transformed to heat per coulomb of charge that flows through the circuit?

A) 0.50 J
B) 9.0 J
C) 3.0 J
D) 72 J

Question 20

The current in an electron beam in a cathode-ray tube is measured to be 280 µA.How many electrons hit the screen in 50 s? (e = 1.6 × 10−¹⁹ C)

A) 2.2 × 10¹¹ electrons
B) 8.8 × 10¹⁶ electrons
C) 8.8 × 10¹⁵ electrons
D) 2.2 × 10¹⁵ electrons

Question 21

When a 24.0-Ω resistor is connected across a 12.0-V battery,a current of 410 mA flows.What is the resulting terminal voltage of the battery?

A) 11.6 V
B) 9.8 V
C) 0.4 V
D) 12.0 V

Question 22

A solar panel measures 80 cm × 50 cm.In direct sunlight,the panel delivers 4.8 A at 15 V.If the intensity of sunlight is 1000 W/m²,what is the efficiency of the solar panel in converting solar energy into electrical energy?

A) 12%
B) 24%
C) 18%
D) 6.0%

Question 23

Three 3.0-Ω resistors are connected in parallel to a 12.0-V battery.What is the current in any one of the resistors?

A) 0.75 A
B) 12 A
C) 4.0 A
D) 1.3 A

Question 24

If ε = 9.0 V,what is the current in the 30-Ω resistor?

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

Question 25

If ε = 20 V,at what rate is thermal energy being generated in the 40-Ω resistor?

A) 26 W
B) 1.6 W
C) 3.3 W
D) 15 W

Question 26

Three resistors connected in parallel have individual values of 4.0,6.0,and 10.0 Ω,respectively.If this combination is connected in series with a 12-V battery and a 2.0-Ω resistor,what is the current in the 6.0-Ω resistor?

A) 0.98 A
B) 16 A
C) 0.59 A
D) 11 A

Question 27

If a lamp has resistance of 120 Ω when it operates at 200 W,what is the applied voltage?

A) 120 V
B) 220 V
C) 110 V
D) 155 V

Question 28

An 10.0-Ω resistor is dissipating 100 watts.What are the current through it and the difference of potential across it?

A) 31.6 A,3.16 V
B) 10.0 A,3.16 V
C) 3.16 A,31.6 V
D) 3.16 A,10.0 V

Question 29

A water pump draws about 4.4 A when connected to 240 V.What is the cost (with electrical energy at 9 cents per kWh)of running the pump for 10 h?

A) 82 cents
B) 8.0 cents
C) 95 cents
D) 15 cents

Question 30

A resistor is connected to a battery with negligible internal resistance.If you replace the resistor with one that has quadruple the resistance,by what factor does the power dissipated in the circuit change?

A) 0.25
B) 4.0
C) 2.0
D) 0.50

Question 31

A high-voltage transmission line carries 500 A at 700 kV for a distance of 100 miles.If the resistance in the wire is 1 Ω/mile,what is the power loss due to resistive losses?

A) 250 MW
B) 2.5 kW
C) 25 MW
D) 25 kW

Question 32

Three resistors,each of different value,are used in a circuit with a power source supplying 12 volts.For which of the following resistor combinations is the total power supplied the greatest?

A) This cannot be found until it is known which resistor is in series with the parallel pair.
B) all three resistors in series
C) two of the resistors in parallel with the third resistor in series with the parallel pair
D) all three resistors in parallel

Question 33

Two resistors of values 6.0 and 12.0 Ω are connected in parallel.This combination in turn is hooked in series with an 8.0-Ω resistor and a 24-V battery.What is the current in the 12-Ω resistor?

A) 1.3 A
B) 4.0 A
C) 12 A
D) 0.67 A

Question 34

When a 24.0-Ω resistor is connected across a 12.0-V battery,a current of 410 mA flows.What is the internal resistance of the battery?

A) 29.3 Ω
B) 0.9 Ω
C) 5.3 Ω
D) 0.02 Ω

Question 35

A light bulb,sold as long-lasting,is rated 120 W at 130 V.The "increased" lifetime comes from using it at 120 V.Assuming negligible change in resistance at the different voltage,what is its power consumption at 120 V?

A) 92 W
B) 102 W
C) 108 W
D) 85 W

Question 36

A high-voltage transmission line carries 500 A at 700,000 V.What is the power carried by the line?

A) 100 MW
B) 350 MW
C) 700 MW
D) 70 MW

Question 37

Four 8.0-Ω resistors are connected in parallel.What is their equivalent resistance?

A) 4.0 Ω
B) 0.50 Ω
C) 2.0 Ω
D) 32 Ω

Question 38

If a 500-W heater carries a current of 2.00 A,what is the voltage across the ends of the heating element?

A) 2000 V
B) 125 V
C) 0.008 V
D) 250 V

Question 39

An electric clothes dryer draws 20 A at 220 V.If the clothes put into the dryer have a mass of 7.0 kg when wet and 3.0 kg dry,how long does it take to dry the clothes? (Assume all heat energy goes into vaporizing water,L_v = 2.26 × 10⁶ J/kg. )

A) 55 min
B) 26 min
C) 16 min
D) 34 min

Question 40

An electric car is designed to run off a bank of 12-V batteries with total energy storage of 6.0 × 10⁷ J.If the electric motor draws 6000 W in moving the car at a steady speed of 10 m/s,how far will the car go before it is "out of juice?"

A) 150 km
B) 50 km
C) 100 km
D) 25 km

Question 41

What is the current through the 6-Ω resistor?

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

Question 42

In order for a circuit to respond quickly,its time constant should be short.In a circuit involving resistance and capacitance,which of the following choices would result in the shortest time constant?

A) R = 75 Ω,C = 75 μF
B) R = 200 Ω,C = 200 μF
C) R = 300 Ω,C = 75 μF
D) R = 100 Ω,C = 30 μF

Question 43

A 100-W bulb and a 40-W bulb,each designed for an applied voltage of 120 V,are connected in series across a 120-V source.What are the voltages across the 100-W bulb and across the 40-W bulb?

A) 86 V,34 V
B) 30 V,90 V
C) 90 V,30 V
D) 34 V,86 V

Question 44

What is the maximum number of 60-W light bulbs you can connect in parallel in a 120-V home circuit without tripping the 20-A circuit breaker?

A) 3600
B) 59
C) 11
D) 39

Question 45

Five resistors each have resistance R.Three of the resistors are connected in series and this combination is then connected in parallel with the two other resistors which have been connected in series with each other.What is the equivalent resistance for this arrangement?

A)

B)

C)

D)

Question 46

In a circuit involving resistance and capacitance,which of the following choices would result in the longest time constant?

A) R = 100 Ω,C = 30 μF
B) R = 300 Ω,C = 150 μF
C) R = 75 Ω,C = 75 μF
D) R = 200 Ω,C = 200 μF

Question 47

In circuits involving resistors and capacitors the quantity 63% often arises.Which of the following is equivalent to this quantity?

A) e​^-2
B) 1 - e​^-1
C) 1 - e​^-2
D) e​^-1

Question 48

The following three appliances are connected to a 120-V house circuit: i)toaster,1200 W,ii)coffee pot,750 W,and iii)microwave,1000 W.If all were operated at the same time,what total current would they draw?

A) 5.0 A
B) 25 A
C) 23 A
D) 6.0 A

Question 49

Consider the circuit shown in the figure.What power is dissipated by the top 5-Ω resistor?

A) 14 W
B) 112 W
C) 17 W
D) 52 W

Question 50

Resistors of values 8.0 Ω,12.0 Ω,and 24.0 Ω are connected in parallel across a fresh battery.Which resistor dissipates the least power?

A) the 24.0-Ω resistor
B) All dissipate the same power when in parallel.
C) the 12.0-Ω resistor
D) the 8.0-Ω resistor

Question 51

If I = 1.0 mA and the potential difference,V_A - V_B = +30 V in the circuit segment shown,determine the charge and polarity of the capacitor.

A) 1.0 mC,left plate is positive
B) 3.5 mC,right plate is positive
C) 3.5 mC,left plate is positive
D) 1.0 mC,right plate is positive

Question 52

A series RC circuit consists of a battery,a switch,a resistor,and a capacitor.In terms of the time constant
Of this circuit,how long after the switch is closed does the current in the circuit reach half of its maximum value?

A) 0.500

B) 1.50

C) 0.693

D) 2.00

Question 53

A hair dryer draws 1500 W,a curling iron draws 800 W,and an electric light fixture draws 500 W.If all three of these appliances are operating in parallel on a 120 V circuit,what is the total current drawn?

A) 23.3 A
B) 20.8 A
C) 36.7 A
D) 19.4 A

Question 54

To measure the current through and the voltage across a resistor in a circuit,you should place the ammeter in _____ with the resistor and the voltmeter in _____ with the resistor.

A) series,series
B) parallel,series
C) parallel,parallel
D) series,parallel

Question 55

Four 1.5-volt AA batteries in series power a transistor radio.If the batteries hold a total charge of 440 C,how long will they last if the radio has a resistance of 200 Ω?

A) 4.1 h
B) 2.2 h
C) 1.1 h
D) 13 h

Question 56

An RC circuit with resistance R​₀ and capacitance C​₀ has a time constant τ​₀.Which of the following additions to the circuit would result in the time constant doubling?

A) a capacitor with capacitance 3C​₀ in series with the original C​₀
B) a capacitor with capacitance C​₀ in series with the original C​₀
C) a capacitor with capacitance 3C​₀ in parallel with the original C​₀
D) a capacitor with capacitance C​₀ in parallel with the original C​₀

Question 57

What is the current flowing through the 8-Ω resistor?

A) 6 A
B) 4 A
C) 2 A
D) 1 A

Question 58

In the circuit segment shown if I = 8.0 mA and Q = 75 µC,what is the potential difference,V_A - V_B?

A) −35 V
B) +15 V
C) -15 V
D) +35 V

Question 59

A battery has an internal resistance R_int.Connecting a wire of negligible resistance between the terminals of the battery draws the maximum current I​_max from this battery.If instead a resistor is connected between the terminals,a smaller current is produced.What value resistor placed across the terminals would result in the current produced to be half of I​_max?

A) 0.63R_int
B) R_int
C) 0.50R_int
D) 0.37R_int

Question 60

A series RC circuit has a time constant of 1.5 s.The battery has a voltage of 50 V and the maximum current just after closing the switch is 500 mA.The capacitor is initially uncharged.What is the charge on the capacitor 3.0 s after the switch is closed?

A) 0.48 C
B) 0.86 C
C) 0.43 C
D) 0.99 C

Question 61

A metal wire has a resistance of 10.00 Ω at a temperature of 20.0°C.If the same wire has a resistance of 10.55 Ω at 90°C,what is the resistance when its temperature is 0.0°C?

A) 13.8 Ω
B) 9.69 Ω
C) 9.84 Ω
D) 0.70 Ω

Question 62

Carbon has a negative temperature coefficient of resistance of -0.5 × 10^-3 (°C)−¹.What temperature increase would result in a resistance decrease of 3% for a carbon resistor?

A) 60°C
B) 100°C
C) 20°C
D) 40°C

Question 63

A 22-Ω platinum wire at 20°C with a temperature coefficient of resistivity of 3.9 × 10−³ (°C)−¹ will have what resistance at 100°C?

A) 29 Ω
B) 20 Ω
C) 26 Ω
D) 14 Ω

Question 64

The resistance of a platinum wire is to be calibrated for low-temperature work.A platinum wire with resistance 2.000 Ω at 20°C is immersed in liquid nitrogen at 77 K (−196°C).If the temperature response of the platinum wire is linear,what is the expected resistance of the platinum wire at −196°C? [α_platinum = 3.92 × 10−³ (°C)−¹].

A) 0.153 Ω
B) 1.768 Ω
C) 3.69 Ω
D) 0.307 Ω

Question 65

A metal wire has a resistance of 25.00 Ω under room temperature conditions of 25°C.When the wire is heated to 85°C the resistance increases by 1.95 Ω.What is the temperature coefficient of resistivity of this metal?

A) 1.3 × 10−³ (°C)−¹
B) 1.5 × 10−³ (°C)−¹
C) 5.0 × 10−⁴ (°C)−¹
D) 2.5 × 10−³ (°C)−¹

Question 66

A tungsten wire is used to determine the melting point of indium.The resistance of the tungsten wire is 6.000 Ω at 20°C and increases to 9.700 Ω as the indium starts to melt.α_tungsten = 4.50 × 10−³ (°C)−¹.What is the melting temperature of indium?

A) 351°C
B) 731°C
C) 132°C
D) 157°C

Question 67

A certain material is in a room at 27°C.If the absolute temperature (K)of the material is tripled,its resistance quadruples.(Water freezes at 273 K. )What is the value for α,the temperature coefficient of resistivity?

A) 0.0050 (°C)−¹
B) 0.0025 (°C)−¹
C) 1 (°C)−¹
D) 3 (°C)−¹