Please answer all! Answer the following questions on a ParSCORE Test Form (7 pts

Question

Please answer all!

Answer the following questions on a ParSCORE Test Form (7 pts per question): 1. A certain toaster has a heating element made of Nichrome resistance wire. When the toaster is first connected to a 120-v source of potential difference (and the wire is at a temperature of 20.0°C), the initial current is 1.80 A, but the current begins to decrease as the resistive element warms up when the toaster reaches its final operating temperature, the current has dropped to 1.53 A. What is the final temperature of the heating element? A. 385°C B. 424°C C. 461c D. 498c E. 520°C 2. In the figure below, the current is measured with the ammeter on the right side of the circuit diagram. when the switch is closed, the reading on the ammeter A. increase B. decrease C. does not change D. Can increase or decrease 3. A car owner forgets to turn off the headlights of his car while it is parked in his garage. If the 12.0-v battery in his car is rated at 42.0 A h and each headlight requires 38.4 W of power, how long will it take the battery to completely discharge? A. 6.56 hours B. 7.25 hours C. 8.15 hours D. 9.78 hours E. 10.3 hours 4. Two resistors, A and B, are connected in series circuit with a battery. The resistance of B is half that of A. In which resistor the current is higher? A. resistor A B. resistor B C. Current is the same D. Potential difference is the same E. More information is needed 5. The cost of electricity varies widely throughout the United States; $0.140/kWh is a typical value. At this unit price, calculate the cost of making a piece of dark toast in 3.00 min with a 900-W toaster. A. 4.25 cents B. 1.58 cents C. 0.745 cents D. 0.596 cents E. 0.630 cents

Explanation / Answer

2.

A.

when the switch is closed , the overall resistance of the circuit becomes smaller since combination of resistances in parallel is smaller than the indivisual resistances. as the total resistance decreases, the current in the circuit increases and hence the reading of the ammeter increases.

3.

P = power in each headlight = 38.4 Watt

V = battery Voltage = 12 Volts

i = current in each headlight = P/V = 38.4/12 = 3.2 A

itotal = total current given out by battery = 2 i = 2 x 3.2 = 6.4 A

Q = charge = 42 Ah

t = time

using the equation

t = Q/itotal = 42/6.4 = 6.56 h

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