Chapters 2 6 (021)
Q13 A copper wire of cylindrical shape has resistance R. What is the resistance of a second wire, made of the same material, that is twice as long and has twice the diameter?
A1 R/2
A2 R/4
A3 R
A4 2R
A5 4R
Q14 At T = 20 degrees-C, the length of a wire is 10 m, and its cross sectional area is 0.50 mm**2. A potential difference of 1.0 V is maintained across the ends of the wire. The resistance of the wire changes by 0.30 ohms for a temperature change of
50 Celsius degrees. What is the temperature coefficient of resistivity of the wire?
At T = 20 degrees, the resistivity is 5.0*10**(-6) ohm*m.

A1 6.0*10**(-5) degrees**(-1)
A2 6.0*10**(-4) degrees**(-1)
A3 15*10**(-5) degrees**(-1)
A4 15*10**(-4) degrees**(-1)
A5 15*10**(-3) degrees**(-1)
Q15 A current of 0.300 A is passed through a lamp for 2.00 minutes using a 6.00-V battery. The energy dissipated by the lamp during the 2.00 minutes is:
A1 216 J
A2 36.0 J
A3 1.80 J
A4 12.0 J
A5 20.0 J

19 In one hour, how many electrons pass between the terminals of a 12-V car battery when a 96 watts headlight is used?
A1 1.8*10**23 electrons.
A2 6.6*10**22 electrons.
A3 2.6*10**19 electrons.
A4 2.8*10**23 electrons.
A5 5.0*10**19 electrons.
20 A resistance operated at 110
Volts has a power output of 100
Watt. What is the percentage increase of the power if the voltage increases to 121 volts?
(Assume that the resistance stays constant.)
A1 21%.
A2 25%.
A3 0.9%.
A4 3.7%.
A5 11%.

S-27-3
A small sphere that carries a charge of 8.00 nC is whirled in a circle at the end of an insulating string. The angular frequency of rotation is 100

rad/s. What average current does this rotating charge represent?
S-27-22
Aluminum and copper wires of equal length are found to have the same resistance. What is the ratio of their radii?
S-27-30
The rod in the figure is made of two materials. Both have a square cross section 3.0 mm on a side. The first material has a resistivity of 4.0 x
10 -3

m and is 25 cm long, while the second material has a resistivity 6.0 x
10 -3

m and is 40 cm long. What is the resistance between the two ends of the rod?
S-27-32
The resistance of a platinum wire is to be calibrated for lowtemperature measurements. A platinum wire has a resistance
1.00

at 20 o C. If the temperature response of the platinum wire is linear, what is the expected resistance of the platinum wire when it is immersed in liquid nitrogen (at 77 K)? Assume
 platinum
= 3.92 x
10 -3 / o C.
~S-27-52
The heating element of a coffee maker operates at 120 V and carries a current of 2.0 A. Assuming that 20 % of the heat generated is absorbed by the water, how long does it take to heat

100 g of water from room temperature (23 o C) to the boiling point?

S-27-19
A 12

wire is cut into three equal pieces that are then connected side by side to form a new wire the length of which is
1/3 the original length. What is the resistance of this new wire?
S-27-21
A wire with a resistance 100

is lengthened to 1.25 times its original length by pulling it through a small hole. Find the resistance of the wire after it is stretched.
S-27-31
What is the fractional change in the resistance of an iron filament when its temperature changes from 25 o C to 50 o C?
Assume
 iron
= 5.0 x
10 -3 / o C.