suppose that a voltage surge produces 140 v for a moment in a 120 v-line. what will temporarily be...
TRANSCRIPT
Suppose that a voltage surge produces 140 V for a moment in a 120 V-line. What will temporarily be the output of a 100 W lightbulb assuming its resistance does not change?
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1. 109 W
2. 118 W
3. 127 W
4. 136 W
A solar panel measures 80 cm x 50 cm. In direct sunlight, the panel delivers 3.2 A at 15 V. If the intensity of sunlight is 1000 W/m 2 , what is the efficiency of the solar panel in converting solar energy into electrical energy?
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1. 24.0%
2. 18.0%
3. 12.0%
4. 6.0%
A steam turbine at an electric power plant delivers 4500 kW of power to an electrical generator which converts 95% of this mechanical energy into electrical energy. What is the current delivered by the generator if it delivers at 3600 V?
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1. 0.66 x 103 A
2. 1.0 x 103 A
3. 1.19 x 103 A
4. 5.9 x 103 A
The heating coil of a hot water heater has a resistance of 20 ohm and operates at 210 V. How long a time is required to raise the temperature of 200 kg of water from 15°C to 80 °C? (the specific heat for water = 103 cal/kg-°C and 1.0 cal = 4.186 J)
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1. 1.7 hr
2. 3.8 hr
3. 5.1 hr
4. 6.9 hr
The heating coil of a hot water heater has a resistance of 20 ohm and operates at 210 V. If electrical energy costs 5.5 cents per kW-hr, what does it cost to raise the 200 kg water temperature form 15°C to 80°C? (the specific heat of water = 103 cal/kg°C and 1.0 cal = 4.186 J)
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1. 48 cents
2. 83 cents
3. 16 cents
4. 80 cents
An electric clothes dryer draws 15 A at 220 V. If the clothes put into the dryer have a mass of 7 kg when wet and 4 kg dry, how long does it take to dry the clothes? (Assume all heat energy goes into vaporizing water, Lvap = 2.26 x 106 J/kg.)
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1. 55.1 min
2. 34.2 min
3. 20.0 min
4. 15.6 min
By what factor is the resistance of a copper wire changed when its temperature is increased from 20°C to 120°C? (the temperature coefficient of resistivity for copper = 3.9 x 10-3 /°C)
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1. 0.72
2. 1.06
3. 1.39
4. 1.44
If a lamp is measured to have a resistance of 120 ohms when it operates at a power of 100 W, what is the applied voltage?
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1. 110 V
2. 120 V
3. 125 V
4. 220 V
If a lamp has a resistance of 120 ohms when it operates at a power of 100 W, what current does the lamp carry?
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1. 2.10 A
2. 1.2 A
3. 0.91 A
4. 0.83 A
An electric toaster requires 1100 W at 110 Volts. What is the resistance of the heating coil?
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1. 7.5 W
2. 9.0 W
3. 10.0 W
4. 11.0 W
If a 500 W heater carries a current of 4.0 A, how much does it cost to operate the heater for 30 min if electrical energy costs 6 cents per kW-hr?
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1. 1.5 cents
2. 9.0 cents
3. 18.0 cents
4. 36.0 cents
A metal wire has a resistance of 10.00 ohms at a temperature of 20°C. If the same wire has a resistance of 10.55 ohms at 90°C, what is the resistance of this same wire when its temperature is -20°C?
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1. 0.7 W
2. 9.69 W
3. 10.31 W
4. 13.8 W
If a 500 W heater carries a current of 4.0 A, what is the voltage across the ends of the heating element?
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1. 2000 V
2. 125 V
3. 250 V
4. 0.008 V
If a 500 W heater carries a current of 4.0 A, what is the resistance of the heating element?
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1. 85.7 W
2. 42.8 W
3. 31.3 W
4. 11.2 W
A metal wire has a resistance of 10.00 ohms at a temperature of 20°C. If the same wire has a resistance of 10.55 ohms at 90°, what is the temperature coefficient of resistivity of this metal?
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1. 7.8 x 10-4/°C
2. 12.7 x 10-4/°C
3. 0.78 x 10-4/°C
4. 1.27 x 10-4/°C
A wire carries a steady current of 0.1 A over a period of 20 s. What total charge passes through the wire in this time interval?
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1. 200 C
2. 20 C
3. 2.0 C
4. 0.005 C
A 0.20 m long metal wire has a radius of 1 cm and a resistance of 3.2 x 10-5 ohm. What is the resistivity of the metal?
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1. 1.6 x 10-8 ohm-m
2. 5.0 x 10-8 ohm-m
3. 16.0 x 10-8 ohm-m
4. 160 x 10-8 ohm-m
A nichrome wire has a radius of 0.50 mm and a resistivity of 1.5 x 10-6 ohm-m. What is the resistance per unit length of this wire?
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1. 0.0015 ohm-m
2. 0.95 ohm-m
3. 1.6 ohm-m
4. 1.9 ohm-m
A nichrome wire has a radius of 0.50 mm and a resistivity of 1.5 x 10-6 ohm-m. If the wire carries a current of 0.5 A, what is the potential difference per unit length along this wire?
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1. 0.003 V/m
2. 0.95 V/m
3. 1.6 V/m
4. 1.9 V/m
When an electric current exists within a conducting wire, which of the following statements describes the condition of any accompanying electric field?
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1. must be zero
2. must be parallel to current flow
3. must be anti-parallel to current flow
4. must be perpendicular to current flow
A high-voltage transmission line carries 1000 A at 700 kV for a distance of 100 miles. If the resistance in the wire is 1 W/mile, what is the power loss due to resistive losses?
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1. 10 kW
2. 100 kW
3. 10 MW
4. 100 MW
A copper cable is to be designed to carry a current of 300 A with a power loss of only 2 Watts per meter. What is the required radius of the copper cable? (The resistivity of copper is 1.7 x 10-8 W-m)
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1. 0.8 cm
2. 1.6 cm
3. 3.2 cm
4. 4.0 cm
An electric car is designed to run off a bank of 12-V batteries with total energy storage of 2 x 107 J. If the electric motor draws 8000 W, what is the current delivered to the motor?
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1. 666 A
2. 444 A
3. 222 A
4. 111 A
A high-voltage transmission line carries 1000 A at 700,000 V. What is the maximum power carried in the line?
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1. 700 MW
2. 370 MW
3. 100 MW
4. 70 MW
An electric car is designed to run off a bank of 12-V batteries with total energy storage of 2 x 107 J. If the electric motor draws 8000 W in moving the car at a steady speed of 20 m/s, how far will the car go before it is "out of juice"?
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1. 25 km
2. 50 km
3. 100 km
4. 150 km
A color television set draws about 2.5 A when connected to 120 V. What is the cost (with electrical energy at 6¢/kWh) of running the color TV for 8 hours?
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1. 1.4¢
2. 3.0¢
3. 14.4¢
4. 30.0¢
A high voltage transmission line of diameter 2 cm and length 200 km carries a steady current of 1000 A. If the conductor is copper with a free charge density of 8 x 1028 electrons/m3 , how long does it take one electron to travel the full length of the cable? (q = 1.6 x 10-19 C)
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1. 8 x 102 s
2. 8 x 104 s
3. 8 x 106 s
4. 8 x 108 s
The resistance of a platinum wire is to be calibrated for low-temperature work. A platinum wire with resistance 1 W at 20°C is immersed in liquid nitrogen at 77 K (-196°C). If the temperature response of the platinum wire in linear, what is the expected resistance of the platinum wire at -196°C?(aplatinum = 3.92 x 10-3 /°C)
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1. 0.153 W
2. 0.232 W
3. 1.768 W
4. 1.847 W
Some superconductors are capable of carrying a very large quantity of current. If the measured current is 105 A, how many electrons are moving through the superconductor per second? (qe = 1.6 x 10-19 C)
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1. 6.25 x 1023
2. 3.12 x 1022
3. 6.25 x 1021
4. 3.12 x 1020
A platinum wire is utilized to determine the melting point of indium. The resistance of the platinum wire is 2 W at 20°C and increases to 3.072 W as the indium starts to melt. aplatinum = 3.92 x 10-3 /°C. What is the melting temperature of
indium?
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1. 137°C
2. 157°C
3. 351°C
4. 731°C
Which is not a force?
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1. Gravity
2. Electrical force
3. Electromotive force
4. Friction
The unit of electric current, the ampere, is dimensionally equivalent to which of the following?
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1. volt x ohm
2. volt/ohm
3. ohm x meter
4. volt/sec
The unit of electric resistance, the ohm, is dimensionally equivalent to which of the following?
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1. volt/amp
2. volt x meter
3. amp/sec
4. amp/meter
What happens to the resistance of a superconductor when its temperature drops below the critical temperature?
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1. equals that of a semiconductor of equal dimensions
2. increases by two
3. drops to zero
4. reduces to one-half
The quantity, electromotive force, is dimensionally equivalent to which of the following?
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1. joule x meter
2. joule x coulomb
3. coulomb/ohm
4. joule/coulomb
The unit for rate of energy transformation, the watt, in an electric circuit is dimensionally equivalent to which of the following?
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1. volt/sec
2. ampere x ohm
3. volt x ampere
4. volt/ohm
The current in an electron beam in a cathode-ray tube is measured to be 70 µ A. How many electrons hit the screen in 5 seconds? (qe = 1.6 x 10-19 C)
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1. 2.19 x 1011 electrons
2. 8.75 x 1013 electrons
3. 2.19 x 1015 electrons
4. 8.75 x 1018 electrons
If a 6 V battery, with negligible internal resistance, and a 12 ohm resistor are connected in series, what is the amount of electrical energy transformed to heat per coul of charge that flows through the circuit?
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1. 0.50 J
2. 3.0 J
3. 6.0 J
4. 72 J
If a 75 W lightbulb operates at a voltage of 120 V, what is the current in the bulb?
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1. 0.63 A
2. 1.6 A
3. 9.0 x 103 A
4. 1.1 x 10-4 A
Tripling the current in a circuit with constant resistance has the effect of changing the power by what factor?
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1. 0.33
2. 1/9
3. 3.0
4. 9.0
Replacing a wire resistor with another of the same material and length but with three times the diameter will have the effect of changing the resistance by what factor?
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1. 0.33
2. 1/9
3. 3.0
4. 9.0
The size of the electric current in an electrical conductor is a function of which of the following?
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1. velocity of charge carriers
2. conductor thickness
3. density of charge carriers
4. all of the choices are valid
A superconducting wire's chief characteristic is which of the following?
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1. an extremely great length
2. a large cross-sectional area
3. an extremely high temperature
4. no resistance
When current is flowing in a superconductor, which statement is not true?
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1. A battery keeps the current going.
2. Electrical charges are moving.
3. The resistance is zero.
4. No power is given off in the form of heat.
Ten coulombs of charge start from the negative terminal of a battery, flow through the battery and then leave the positive terminal through a wire, flow through a resistor and then return to the starting point on this closed circuit. In this complete process, the ten coulombs
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1. do positive work on the battery.
2. receive heat energy from the resistor.
3. have a net loss of potential energy.
4. have no net change in potential energy.
Which process will double the power given off by a resistor?
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1. Doubling the current while doubling the resistance
2. Doubling the current by making the resistance half as big
3. Doubling the current by doubling the voltage
4. Doubling the current while making the voltage half as big
In a carbon microphone, the change in resistance in the microphone as the sound wave moves the diaphragm back and forth is caused by the
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1. change in length of the carbon resistance.
2. change in temperature of the carbon resistance.
3. change in voltage across the carbon resistance.
4. change in velocity of the carbon resistance.
Which is a unit of power?
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1. Kilowatt-hour
2. Watt per sec
3. Ampere ohm
4. Joule per sec
If a certain resistor obeys Ohm's law, its resistance will change
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1. as the voltage across the resistor changes.
2. as the current through the resistor changes.
3. as the energy given off by the electrons in their collisions changes.
4. none of the choices, since resistance is a constant for a given resistor.
Consider some material that has been cooled until it has become a superconductor. If it is cooled even further its resistance will
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1. increase
2. decrease
3. stay constant and non-zero
4. none of the choices
A certain material is in a room at 27°C. If the absolute temperature (°K) of the material is doubled, its resistance also doubles. (Water freezes at 273°K.) What is the value for a, the temperature coefficient of resistivity?
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1. 1/°C
2. 2/°C
3. 0.0033/°C
4. 0.038/°C
When you flip a switch to turn on a light, the delay time before the light turns on is determined by
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1. the number of electron collisions per second in the wire.
2. the drift speed of the electrons in the wire.
3. the speed of the electric field moving in the wire.
4. none of these, since the light comes on instantly.
A flashlight bulb operating at a voltage of 4.5 V has a resistance of 8 ohm. How many electrons pass through the bulb filament per second (qe = 1.6 x 10-19 coul)
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1. 3.7 x 1016
2. 1.8 x 1021
3. 9.4 x 1017
4. 3.5 x 1018
In a certain material there is a current of 16 A flowing through a surface to the right, and there is an equal amount of positive and negative charge passing through the surface producing the current. How much negative charge passes through the surface?
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1. 8 C/s toward the right
2. 8 C/s toward the left
3. 16 C/s toward the right
4. 16 C/s toward the left
A lightbulb has a resistance of 240 W when operating at a voltage of 120 V. What is the current in the lightbulb?
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1. 2.0 A
2. 1.0 A
3. 0.5 A
4. 0.2 A
Number 10 copper wire (radius = 1.3 mm) is commonly used for electrical installations in homes. What is the voltage drop in 40 meters of #10 copper wire if it carries a current of 10 Amps? (The resistivity of copper is 1.7 x 10-8 W-m.)
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1. 1.28 volts
2. 0.77 volts
3. 0.50 volts
4. 0.13 volts
If a metallic wire of cross-sectional area 3.0 x 10-6 m2 carries a current of 6 A and has a mobile charge density of 4.24 x 1028 carriers/m3 what is the average drift velocity of the mobile charge carriers? (charge value = 1.6 x 10 -19 coul)
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1. 3.4 x 103 m/s
2. 1.7 x 103 m/s
3. 1.5 x 10-4 m/s
4. 2.9 x 10-4 m/s
What is the resistivity of a metallic conductor, 30 m long, with a uniform cross-sectional area of 3.0 x 10-6 m2 and a resistance of 180 ohm?
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1. 0.056 x 106 ohm-m
2. 18 x 10-6 ohm-m
3. 162 x 10-4 ohm-m
4. 18 x 108 ohm-m
What is the potential difference across a 5 ohm resistor which carries a current of 5 A?
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1. 100 V
2. 25 V
3. 4 V
4. 1 V
A 20 ohm platinum wire at 20°C with a temperature coefficient of resistivity of 3.9 x 10-3 /°C will have what resistance at 100°C?
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1. 14 W
2. 20 W
3. 26 W
4. 28 W