Page 299 - Schaum's Outline of Theory and Problems of Applied Physics

284 ELECTRIC CURRENT [CHAP. 24

Multiple-Choice Questions

24.1. The same volume of copper can have any of the following combinations of length L and cross-sectional area A.
Which combination has the most resistance?
(a) L and A
(b) L/2 and 2A
(c)2L and A/2
(d) All have the same resistance because the volume of copper is the same.

24.2. The area in circular mils of a circle whose diameter is d mils is
(a) d (c) πd
(b) d 2 (d) πd 2

24.3. A certain wire has the resistance R. Another wire, exactly the same except having twice the diameter, has the
resistance
(a) 1 R (c) 2R
4
(b) 1 R (d) 4R
2
24.4. When a copper wire is heated, its resistance
(a) decreases
(b) remains the same
(c) increases
(d) any of the above, depending on the temperatures

24.5. Which one or more of the following combinations of units is equal to the watt?
(a) J/s (c) A
2
2
2
(b) V /A (d) V
24.6. The diameter of a wire whose cross-sectional area is 2500 cmil is
(a) 0.016 in. (c) 0.050 in.
(b) 0.025 in. (d) 0.056 in.

24.7. The resistivity of copper is 1.7 × 10 −8 ·m. The diameter of a 50-m length of copper wire whose resistance is
1.2 is
(a) 0.47 mm (c) 0.90 mm
(b) 0.84 mm (d) 0.95 mm

24.8. The resistance of a 120-V light bulb that draws a current of 1.25 A is

(a) 9.8 (c) 96
(b) 77 (d) 150

24.9. A 120-V appliance that draws a current of 20 A has a power rating of
(a) 6 W (c) 2.4 kW
(b) 0.72 kW (d) 48 kW

24.10. A light bulb rated at 240 V, 150 W is connected to a 120-V power line. The current that flows in it is

(a) 0.313 A (c) 1.25 A
(b) 0.625 A (d) 1.88 A