Exam 5: Current and Resistance

A high-resistance material is used as an insulator between the conductors of a length of coaxial cable.The resistance material, which forms a hollow tube, has an inner radius a and an outer radius b, and the insulator provides a resistance R between the conductors.If a second insulator, made of the same material and having the same length, is made with double both the inner radius and the outer radius of the first, what resistance would it provide between the conductors?

The heating coil of a hot water heater has a resistance of 20 ohms and operates at 210 V.If electrical energy costs 5.5 cents per kW-hr, what does it cost to raise the 200 kg of water in the tank from 15 $\degree$ C to 80 $\degree$ C? (The specific heat of water is 4186 J/kg $\degree$ C)

How many electrons pass through a 20- $\Omega$ resistor in 10 minutes if there is a potential drop of 30 volts across it?

How much energy is dissipated as heat during a two-minute time interval by a 1.5-k $\Omega$ resistor which has a constant 20-V potential difference across its leads?

In the Drude model of electrical conduction, the current density is directly proportional to:

If 5.0 *1021 electrons pass through a 20- $\Omega$ resistor in 10 minutes, what is the potential difference across the resistor?

Light bulb A is rated at 60 W and light bulb B is rated at 100 W.Both are designed to operate at 110 V.Which statement is correct?

In the Drude model of electrical conduction, the current density is NOT directly proportional to:

An electric device, which heats water by immersing a resistance wire in the water, generates 50 cal of heat per second when an electric potential difference of 12 V is placed across its leads.What is the resistance of the heater wire? (Note: 1 cal = 4.186 J)

A rod (length = 80 cm) with a rectangular cross section (1.5 mm * 2.0 mm) has a resistance of 0.20 $\Omega$ .What is the resistivity of the material used to make the rod?

What is the resistance of a wire made of a material with a resistivity of 3.2 *10-8 $\Omega$ . m if its length is 2.5 m and its diameter is 0.50 mm?

A rod of 2.0-m length and a square (2.0 mm * 2.0 mm) cross section is made of a material with a resistivity of 6.0 * 10-8 $\Omega$ . m.If a potential difference of 0.50 V is placed across the ends of the rod, at what rate is heat generated in the rod?

A high-voltage transmission line carries 1000 A at 700 kV for a distance of 100 miles.If the resistance per length in the wire is 0.5 $\Omega$ /mile, what is the power loss due to resistive losses?

If a mile of 24-gauge copper wire has a resistance of 0.14 k $\Omega$ and the resistivity of copper is 1.7 * 10-8 $\Omega$ .m, what is the diameter of the wire? (1 mile = 1.6 km)

A nichrome wire and an aluminum wire, each with the same initial resistance, have the same change in resistance when heated separately.( $\rho$ Al = 2.82 * 10-8 $\Omega$ . m; $\alpha$ Al = 3.9 * 10-3 / $\degree$ C; $\alpha$ nichrome = 1.50 *10-6 $\Omega$ . m; $\alpha$ nichrome = 0.40* 10-3 / $\degree$ C.) The ratio of the temperature change of the nichrome wire to the temperature change of the aluminum wire is:

A light bulb is rated at 30 W when operated at 120 V.How much charge enters (and leaves) the light bulb in 1.0 minute?

Most telephone cables are made of copper wire of either 24 or 26 gauge.If the resistance of 24-gauge wire is 137 $\Omega$ /mile and the resistance of 26-gauge wire is 220 $\Omega$ /mile, what is the ratio of the diameter of 24-gauge wire to that of 26-gauge wire?

To increase the current density in a wire of length and diameter D, you can:

A small bulb is rated at 7.50 W when operated at 125 V.The tungsten filament has a temperature coefficient of resistivity $\alpha$ = 4.50 *10-3 / $\degree$ C.When the filament is hot and glowing, its temperature is seven times room temperature (20 $\degree$ C).What is the resistance of the filament (in ohms) at room temperature?

Jadeen says that you can increase the resistance of a copper wire by hammering the wire to make it narrower and longer.Arnell says that you can increase its resistance by heating the wire.Which one, if either, is correct, and why?