39. An incandescent lightbulb is supplied with a constant potential difference of 120 volts. As the filament of the bulb heats up, what happens to 43. An aluminum wire has a resistance of 48 ohms. the resistance of the filament and the current A second aluminum wire of the same length and at the same temperature, but with twice the through it ? cross-sectional area, would have a resistance of (1) The resistance decreases, and the current 1) 120 (2) 240 (3) 48 0 (4) 96 0 decreases. [2) The resistance decreases, and the current 44. What is the resistance of a 10.0-meter-long increases. copper wire having a cross-sectional area of (3) The resistance increases, and the current 1.50 x 1075 meter at 20"C7 decreases. (1) 1.15 x 10-1 0 2) 1.15 x 10 30 (3) 1.15 x 10 #3 n (4) The resistance increases, and the current (4) 1.15 x 10 14 0 increases. 45. A 5.00-meter-long tin wire has a cross-sectional 40. The resistance of a wire at constant temperature area of 2.00 x 10 * meter' and a resistance depends on the wire's of 0.35 ohm, Calculate the resistivity of this tin wire. (1) length, only (2) type of metal, only 46. At 20"C carbon has a resistivity of 3.5 x 10 (3) length and cross-sectional area, only ohm-meter. What is the ratio of the resistivity (4) length, type of metal, and cross-sectional of carbon to the resistivity of copper? area (1) 1:2 41. On the axes below, sketch the general shape of (2) 2:1 (3) 200:1 the graph that shows the relationship between (4) 2000:1 the resistance of a copper wire of uniform cross-sectional area and the wire's length at 47. Unlike most metals, the resistivity of carbon constant temperature. decreases with increasing temperature. As the temperature of carbon increases, its resistance (1) decreases (2) increases (3) remains the same Resistance 48. An aluminum wire and a tungsten wire have the same cross-sectional area and the same resistance at 20"C. If the aluminum wire is 4.0 x 10 meter long, what is the length of Length the tungsten wire? (1) 1.0 x 10 m 42. A piece of wire has a resistance of 8 ohms. What (2) 2.0 x 10 m is the resistance of a second piece of wire of the (3) 4.0 x 10 2 m same composition, same diameter, and at the (4) 8.0 * 10 m same temperature, but with one half the length of the first wire? 37. A potential difference of 12 volts is applied across a circuit having a 4.0-ohm resistance. Calculate the current in the circuit. 38, In the diagrams below, & represents a unit length of copper wire and A represents a unit cross-sectional area. Which copper wire has the smallest resistance at room temperature? (1] (2) (4) 24