Physics II Ch. 17

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

0.0017 (°C)-1

The resistance of a platinum wire is to be calibrated for low-temperature work. A platinum wire with resistance 1.000 W 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? aplatinum = 3.92 ´ 10-3 (°C)-1

0.153 W

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

0.50

A 60-W light bulb is in a socket supplied with 120 V. What is the current in the bulb?

0.50 A

A light bulb has resistance of 240 W when operating at 120 V. Find the current in the light bulb.

0.50 A

If a lamp has a resistance of 120 W when it operates at 100 W, what current does it carry?

0.91 A

A nichrome wire has a radius of 0.50 mm and a resistivity of 1.5 ´ 10-6 W×m. If the wire carries a current of 0.50 A, what is the potential difference per unit length along this wire?

0.95 V/m

A steam turbine at an electric power plant delivers 4 500 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 3 600 V?

1.2 ´ 10^3 A

Number 10 copper wire (radius = 1.3 mm) is commonly used for electrical installations in homes. What is the voltage drop in 40 m of #10 copper wire if it carries a current of 10 A? (The resistivity of copper is 1.7 ´ 10-8 W×m.)

1.3 V

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 ´ 10-3 (°C)-1.

1.39

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 6.0 cents per kWh?

1.5 cents

A nichrome wire has a radius of 0.50 mm and a resistivity of 1.5 ´ 10-6 W×m. What is the resistance per unit length of this wire?

1.9 W/m

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?

1/9

A high-voltage transmission line carries 1 000 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?

100 MW

An electric toaster requires 1 100 W at 110 V. What is the resistance of the heating coil?

11.0 W

If a lamp has resistance of 120 W when it operates at 100 W, what is the applied voltage?

110 V

If a 500-W heater carries a current of 4.00 A, what is the voltage across the ends of the heating element?

125 V

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 light bulb assuming its resistance does not change?

136 W

A tungsten wire is used to determine the melting point of indium. The resistance of the tungsten wire is 3.000 W at 20°C and increases to 4.850 W as the indium starts to melt. atungsten = 4.50 ´ 10-3 (°C)-1. What is the melting temperature of indium?

157°C

A metallic conductor has a resistivity of 18 ´ 10-6 W×m. What is the resistance of a piece that is 30 m long and has a uniform cross sectional area of 3.0 ´ 10-6 m2?

180 W

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?

2 C

Two cylindrical resistors are made of the same material and have the same resistance. The resistors, R1 and R2, have different radii, r1and r2, and different lengths, L1 and L2. Which of the following relative values for radii and lengths would result in equal resistances?

2(r1) = r(2) and 4L1 = L2

The current in an electron beam in a cathode-ray tube is measured to be 70 µA. How many electrons hit the screen in 5.0 s? (e = 1.6 ´10-19 C)

2.2 ´ 10^15 electrons

If a metallic wire of cross sectional area 3.0 ´ 10-6 m2 carries a current of 6.0 A and has a mobile charge density of 4.24 ´ 1028carriers/m3, what is the average drift velocity of the mobile charge carriers? (charge value = 1.6 ´ 10-19 C)

2.9 ´ 10^-4 m/s

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 1% for a carbon resistor?

20°C

A 20-W 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?

26 W

A flashlight bulb operating at a voltage of 4.5 V has a resistance of 8.0 W. How many electrons pass through the bulb filament per second (e = 1.6 ´ 10-19 C)?

3.5 ´ 1018

If a 500-W heater carries a current of 4.00 A, what is the resistance of the heating element?

31.3 W

An electric clothes dryer draws 15 A at 220 V. If the clothes put into the dryer have a mass of 7.0 kg when wet and 4.0 kg dry, how long does it take to dry the clothes? (Assume all heat energy goes into vaporizing water, Lv = 2.26 ´ 106 J/kg.)

34 min

A 0.20-m-long metal rod has a radius of 1.0 cm and a resistance of 3.2 ´ 10-5 W. What is the resistivity of the metal?

5.0 ´ 10-8 W×m

A metal wire has a resistance of 25.00 W under room temperature conditions of 25°C. When the wire is heated to 85°C the resistance increases by 0.75 W. What is the temperature coefficient of resistivity of this metal?

5.0 ´ 10^-4 (°C)^-1

You measure a 25.0-V potential difference across a 5.00-W resistor. What is the current flowing through it?

5.00 A

An electric car is designed to run off a bank of 12-V batteries with total energy storage of 3.0 ´ 107 J. If the electric motor draws 6 000 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?"

50 km

An electric car is designed to run off a bank of 12-V batteries with total energy storage of 3.0 ´ 107 J. If the electric motor draws 6 000 W, what current will be delivered to the motor?

500 A

Some superconductors are capable of carrying a very large quantity of current. If the measured current is 1.00 ´ 105 A, how many electrons are moving through the superconductor per second? (e = 1.60 ´ 10-19 C)

6.25 ´ 10^23

The heating coil of a hot water heater has a resistance of 20 W 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.)

6.9 h

How long is a wire made from 100 cm3 of copper if its resistance is 8.5 ohms? The resistivity of copper is 1.7 x 10-5 W·m.

7.1 m

A high-voltage transmission line carries 1 000 A at 700 000 V. What is the power carried by the line?

700 MW

A high voltage transmission line of diameter 2 cm and length 200 km carries a steady current of 1 000 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)

8 ´ 10^8 s

If electrical energy costs 5.5 cents per kWh, what does it cost to heat 200 kg water from 15°C to 80°C? (The specific heat of water = 103 cal/kg×°C and 1.0 cal = 4.186 J.)

83 cents

A light bulb, sold as long-lasting, is rated 100 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?

85 W

If a 9.0-V battery, with negligible internal resistance, and an 18-W resistor are connected in series, what is the amount of electrical energy transformed to heat per coulomb of charge that flows through the circuit?

9.0 J

A metal wire has a resistance of 10.00 W at a temperature of 20°C. If the same wire has a resistance of 10.55 W at 90°C, what is the resistance when its temperature is -20°C?

9.69 W

When current is flowing in a superconductor, which statement is not true?

A battery is needed to keep the current going.

The size of the electric current in an electrical conductor is a function of which of the following?

All of the above choices are valid.

The resistivity of a material is doubled when heated a certain amount. What happens to the resistance of a resistor made of this material when heated the same amount.

It doubles.

A resistor is made of a material that has a resistivity that is proportional to the current going through it. If the voltage across the resistor is doubled, what happens to the current through it?

It increases by a factor of 21/2.

A resistor is made of a material that has a resistivity that is proportional to the current going through it. If the voltage across the resistor is doubled, what happens to the power dissipated by it?

It increases by a factor of 23/2.

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

It triples.

Two wires with the same resistance have the same diameter but different lengths. If wire 1 has length L1 and wire 2 has length L2, how do L1 and L2 compare if wire 1 is made from copper and wire 2 is made from aluminum? The resistivity of copper is 1.7 ´ 10-5 W·m and the resistivity of aluminum is 2.82´ 10-5 W·m.

L1 = 1.7 L2

The number density of conduction electrons in a metal can be found from the density r of the metal, the mass per mole M of the metal, the number of conduction electrons per metal atom, and Avogadro's number NA. If we assume one conduction electron per atom, which of the following gives the number density of conduction electrons for a given metal?

N(A)r /M

Superconductivity was discovered by:

Onnes.

The unit of electric resistance, the ohm, is equivalent to which of the following?

V/A

The unit of electric current, the ampere, is equivalent to which of the following?

V/W

Which process will double the power given off by a resistor?

doubling the current by making a resistance half as big

When a superconductor's temperature drops below the critical temperature, its resistance:

drops to zero.

When an electric current exists within a conducting wire, which of the following statements describes the condition of any accompanying electric field?

must be parallel to current flow

A superconducting wire's chief characteristic is which of the following?

no resistance

If a certain resistor obeys Ohm's law, its resistance will change:

none of the above, since resistance is a constant for the given resistor.

Materials having resistance changes as voltage or current varies are called:

nonohmic.

A light bulb with a tungsten filament is attached to a source of variable voltage. As the voltage is increased on the bulb,

the bulb's resistance increases.

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

vdA = vdB /4

Which is not a force?

voltage

The temperature coefficient of resistivity for a "perfect" ohmic material would be:

zero.