1. An electric toaster element (Nichrome) is 20 . How great is the current when it is connected to a 120v line? (1)1/6 A(2) 1 A(3) 5 A (4) 6 A (5) 120 A (6) 240 A 0.8A runs through a lamp when attached to a 32v source. What is its resistance? (1) 0.025  (2) 25.6  (3) 32  (4) 40 

2. The resistance of a 10,000 ft (3,048 m) long power line must not exceed 4 . What is the smallest size copper wire that can be used for this line? 4    l /A = (1.70  10 -8  m)(3048m)/A A  1.2954  10 -8 m 2  r 2  1.2954  10 -8 m 2 r  2.03  10 -3 md  4.06 mm Gauge 6 wire or smaller

3. Two wires, A and B, are made of the same metal and have equal length, but the resistance of wire A is four times the resistance of wire B. How do their diameters compare? 1) The diameter of wire A is four times that of wire B 2) The diameter of wire A is twice that of wire B 3) The diameter of wire A is equal to that of wire B 4) The diameter of wire A is one half of that of wire B 5) The diameter of wire A is one quarter of that of wire B

4. A wire of resistance R is stretched uniformly (keeping its volume constant) until it is twice its original length. What happens to the resistance? it increases by a factor 4 1) it increases by a factor 4 it increases by a factor 2 2) it increases by a factor 2 it stays the same 3) it stays the same 4) it decreases by a factor 2 5) it decreases by a factor 4 For a cylinder: Volume = area  length

5. If an electric iron draws 5 Amperes from a 120v line, at what rate is it using power? (1)6 Watts (2) 12 Watts(3) 120 Watts (4) 240 Watts(5) 600 Watts(6) 720 Watts

6. Which has a greater resistance, a 100 Watt lightbulb or a 25 Watt lightbulb? 1) the 25 W bulb 2) the 100 W bulb 3) the same for both Which carries the greater current? 1) the 25 W bulb 2) the 100 W bulb 3) the same for both

7. A 1440 W appliance is designed to operate using a 120 V power source. What is the resistance of the oven? 1) 0.1  2) 10  3) 72  4) need to know the current 5) none of these

8. (4) 6 A (4) 40  (4) The diameter of wire A is one half of that of wire B half the diameter means one quarter the cross sectional area 5) it decreases by a factor 4 Doubling the length alone doubles the resistance, but simultaneously the cross sectional area is halved as well…another doubling! (5) 600 Watts 1)the 25 W bulb 2)the 100 W bulb 2) 10  Answers to the multiple choice questions