Conceptual Physics

to find out what potential difference it actually supplies. You connect it to a 1.25 kȍ resistor and an ammeter (a device that

measures current) and discover that the current through the circuit is 1.03 mA. What is the potential difference?

V

Section 4 - Interactive problem: Ohm’s law

4.1 Use the information given in the interactive problem in this section to calculate the resistance required to achieve the desired
current and give Joe Pasty a nice tan. Test your answer using the simulation.

ȍ

Section 5 - Resistivity

5.1 An automotive junkyard crushes old vehicles into cubes 0.40 m on a side. Assume that these cubes are made of iron. Find
the resistance you would expect to encounter if you connected one wire to the center of a face and one wire to the center of
the opposite face, so that the two faces acted like the ends of a resistor.

ȍ

5.2 A length of nichrome wire (composed of nickel and chromium) is 75.0 cm long and has a rectangular cross section measuring

0.700 mm by 0.500 mm. The resistivity of nichrome is 1.08×10í^6 ȍm. If a potential difference of 225 V is applied between the

two ends of the wire, how much current flows through it?

A

5.3 You have a fine wire with a cross sectional area of 9.4×10í^10 m^2 and a length of 1.1 m. You wish to determine what it is made
out of, so you connect it to a standard AA battery (1.5 V) and measure a current of 0.048 A. What material is the wire most
likely made out of? (Refer to the table in the text.)
i. Silver
ii. Copper
iii. Aluminum
iv. Iron

5.4 12-gauge copper wire has a radius of 1.03×10í^3 m. (a) What is the resistance of 11.5 m of this wire at 20°C? (b) How much

current will pass through the wire if a potential difference of 9.00 V is applied across it?

(a) ȍ

(b) A

5.5 A section of wire 10.0 m long has a resistance of 4.00 ȍ. (a) What is the resistance of 25.0 m of this wire? (b) What is the

resistance of a 10.0 m section of wire of the same material with half the diameter? (c) What is the resistance of a wire whose

length is 20.0 m and diameter is twice as large as the wire in part a?

(a) ȍ

(b) ȍ

(c) ȍ

5.6 The graphite in a pencil has a resistivity of 7.84×10í^6 ȍm. The graphite's diameter is 0.700 mm and its length is 40.0 mm. (a)

Find the resistance of this graphite "wire." (b) Find the diameter of a cylindrical copper wire of the same length (having

resistivity 1.70×10í^8 ȍm) that would produce the same resistance.

(a) ȍ

(b) m

Section 6 - Resistivity and temperature

6.1 A tungsten wire, initially at room temperature (20.0°C) with a resistance between its ends of 41 ȍ, is placed in an oven. What

will the temperature of the wire be when the resistance is 110 ȍ? The temperature coefficient of resistivity of tungsten is

0.0050°Cí^1 at 20.0°C.

°C

6.2 A thermometer can be made from a brass wire (temperature coefficient of resistivity 0.00150°Cí^1 at 20.0°C) which has a

potential difference of 1.50 V between its ends and is connected to an ammeter. A measurement determines that the current

flowing through the wire is 347 mA when the wire is at room temperature (20.0°C). (a) What is the resistance of the wire? (b)

What change in current will accompany a decrease in temperature of one degree Celsius (or one kelvin)? Be careful of the

sign of your answer. (c) How much current flows through the wire when the temperature is 35.0°C?

(a) ȍ

(b) A

(c) A

Copyright 2007 Kinetic Books Co. Chapter 25 Problems^473