Download Electric Circuits: Practice makes Perfect

AP Physics
Electric Circuits:
Practice makes Perfect _____________________
Name
1. Two 40watt light bulbs (at 120V) are connected in parallel. Find
(a) the resistance of each bulb
(b) the current drawn by the circuit
(c) the power used by the circuit
2. A 20 ohm resistor and a 40 ohm resistor are connected in series with a 3.0 volt battery.
Find
(a) the current flowing through the battery
(b) the voltage drop across each resistor
3. A 12 volt battery has an internal resistance r = 0.02 ohms. The battery is used to start
a car via a typical starter motor which should be treated as a simple resistor. While the
motor is turning, it draws 120 amperes and the terminal voltage of the battery is 12.0
volts. What is the resistance of the motor?
4. A 12 volt battery is rated at 100 amp-hours, meaning it can deliver 1 ampere for 100
hours(or 100 amps for one hour).
(a) how many coulombs of charge flow during the discharge of the battery
(b) what amount of energy is delivered during this time?
(c) How much water could this amount of energy heat from freezing to boiling
temperature?
5. Explain why a battery's terminal voltage is greater when it is disconnected from a load
than when it is connected.
6. A pump is intended to lift 3600 liters of water per hour a distance of 10 meters. Find
(a) the minimum horsepower and wattage rating of the pump motor, assuming
100% efficiency
(b) the current drawn by the pump if energized by 12 volts
(c) the resistance of the motor
(d) Draw a circuit that could be used to control the pump so as to change the rate
water is lifted. The circuit should include an ammeter to measure the current
drawn by the pump and a voltmeter that could be used to monitor the state of
discharge of the battery.
7. A heater intended to produce 400 watts is wired, through a switch and an inline fuse,
directly to the terminals of a 100 volt electric car battery. Also wired to the battery
terminals is another circuit consisting of two lamps in series. Each lamp is rated 50
ohms when in normal operation. See diagram below:
fuse
resistance
(a) what current is drawn from the battery (i) when the switch is closed and (ii)
when the switch is open?
(b) What would happen if one lamp burnt out?
What would happen if both lamps were shorted out?
Practice Makes Perfect Answers
1 (a) 360 ohms
(b) 2/3 amps
2. (a) 0.05 amps
3. 0.10 ohms
(c) 80 w
(b) 1v across 20 ohm 2 v across 40 ohm
(emf is 14.4 volts)
4. (a) 3.6 x 105 C
(b) 4.32 x 106 J
(c) 10 Kg
5. will be discussed in class
6. (a) 98 w
(b) 8.2 amps (c) 1.5 ohms (d) diagram
7. (a) (i) 5 amps (ii) 1 amp
(b) other lamp and heater still work
c. heater still works