## Tuesday, 9 December 2014

### ELECTRIC ENERGY , POWER, CURRENT PROBLEMS

Current Definition
1. 3.00 C of charge pass a point in a wire in 3.0 ms. How much current is this?
2. 3.00 X 1012 electrons pass a point in a wire in 0.0060 seconds. What is the current in the wire in
amps?
3. How many electrons pass a point in a conductor in 1 second if the wireʼs current is 0.05 amps?
Ohmʼs Law
4. The fuse for a car radio is a thin wire. The wire is made to burn apart is the current is too high?
What is the resistance of a fuse if it is to burn apart when 2.00 amps pass through it at 240 volts?
5. A light bulb is plugged into a wall outlet. It uses 0.68 A. What is the light bulbʼs resistance?
6. A flash light bulb is labeled to uses 1.77 A. Its resistance is 1.60 Ω. What voltage is the light bulb
rated for?
7 A flashlight light bulb is rated to take 2.83 Volts and use 0.300 amps. What is the resistance of
the filament?
8 Another flash light bulb is rated to use 0.300 A and has a resistance of 4.0 Ω. How much voltage
does this bulb use?
9 A stereo speaker has a resistance of 8.00 Ω. When it is operating at full power (exactly100 watts)
it uses 35 volts of electricity. What is the current drawn by the speaker?
10 A 100 watt light bulb draws 0.83333 amps from a wall outlet (120 volts). What is the resistance of
the light bulbʼs filament?
11 A toaster plugged into the wall, (120 volts), uses 14 amps of electricity. What is the resistance of
the the toaster?
12 The thermostat in a house turns o and off the air conditioner and furnace using 24 volts. What is
the current in the thermostat when it is turned on it if draws 0.100 amps?
13 A motor in a radio control car uses 7.2 volts and draws 14.4 amps of electricity. What is the
resistance of the motor?
14 The volume knob on a radio varies the resistance on a line that goes to the speakers. At a low
volume the resistance is 10,000 Ω. At a high volume the resistance is 10 Ω. If the stereo
maintains 35 volts into the speaker then, what are the two currents going into the speaker?
Current Electricity Basics Worksheet
15 When a battery “dies” the resistance inside the battery rises while the voltage it can produce
almost always remains the same. A new 1.5 volt alkaline battery has a resistance of 0.15 ohms.
an older battery may have a resistance of 15 Ω. how much current is drawn by a new and old
battery?
16 The resistance of dry human skin is about 500,000 Ω and wet, sweaty, human skin is about
1000 Ω. How much current passes across someoneʼs fingers if they touch the leads of a 9 volt
battery when their skin is wet or dry?
17 0.010 Amps causes involuntary muscle contractions. How much voltage is required to cause
involuntary muscle contractions on wet and dry skin?
Power
18 A watch battery is produces a voltage of 1.5 volts. How much power is used by the watch if it
draws 0.001 A?
19 A high tension power line carries 1,000,000 volts of electricity. If the line of to carry 200 Aʼs, then
how power does the power line carry? What is the resistance of the power line?
20 A battery is rated at 1.5 volts. This battery can produce a maximum of 15 W of power.
• How much current can this battery produce?
• What is the resistance of the wire attached to the battery ?
21 A stereo speaker is rated at 8 ohms and 40 watts. A fuse is going to be installed in the speaker.
The fuse can only handle a certain amount of current at 240 volts. How much current does the
fuse need to handle if it is to “blow” at 40 watts?
22 A radio control car uses 7.2 volts and 14 amps. How much power is used by the car?
23 What are the resistances of a 50, 100 and 150 watt light bulb that is plugged into a wall outlet ,
120 volts?
24 A shorted out 12 V car battery can generate 4800 amps! (Never do this. a shorted out battery will
explode.) What is the batteries resistance and how much power is generated by the battery
before it explodes?
25 A hair dyer says it generates 1400 watts. It is plugged into a wall outlet, 120 volts. What is the
current drawn by the hair dryer and what is its resistance?
26 On most home each circuit in a house can handle 15 amps at 120 volts. How much power is
this? Will a 1400 watt hair dryer and four 75 watt light bulbs blow this circuit?
27 The heating element on a stove is connected to a 240 V outlet. The element draws 20 amps
when it is turned on. What is the resistance and power of the element?
28 A motor on a band saw can generate 1/2 horsepower on high. If the motor is plugged into a wall
outlet, how much current will it require? (746 W = hp)
Current Electricity Basics Worksheet
29 The garbage disposal in a sink can generate 3/4 horsepower. If the disposal is plugged into a wall
outlet. How much current does it draw?
30 A small car can generate 95 hp. An equivalent electric vehicle is to be built such that it can
generate the same power as its gasoline counter part. If the electric vehicleʼs motor uses 12
volts, then what is the resistance of the motor? What is the current drawn by the motor? How
many charges are moved by the current if the car runs for 1 hour?
31 What is the current drawn by a household clock-radio using 12 watts?
32 A fan draws 0.184 amps while connected to a wall outlet. What is the power rating of this fan?
33 What is the current drawn by a hair dryer using 1500 watts?
34. What is the current drawn by car stereo that is connected to the car's 12.0 volt battery, if the car
stereo draws 40 watts?
35. What is the battery voltage of a portable radio that draws 0.500 amps and is rated at 1.5 watts?
36 You've just invented a "Do-Hickie" that uses 3.0 volts and draws 3.0 amps. What is the power
rating of your "Do-Hickie?"
37 What is the power rating of a household light bulb that draws 0.60 amps?
38 For the same fuse in problem #4, how much current would it take to burn apart the wire inside
the fuse if it were connected to a 120 volt or a 12 volt source?
39 Stereo speaker is rated to take 100 watts. If the speakerʼs resistance is 8 Ω, How much voltage
is used by the speaker?
40 What is the power rating of a space heater that draws 9.6 amps while connected to a wall outlet?