Worksheet 5: Household Circuits - Modeling Physics

Electric Circuit Model Worksheet 5:
Applications of Electric Circuits
Your house wall outlets provide 120 V.
1. A toaster has 4 amps flowing through it. What is the toaster’s resistance
2. a. Find the current through a 1200 Watt hair dryer.
b. Find the current through a 60 Watt light bulb.
c. What is the resistance (in Ohms) of a 60 Watt light bulb
3. Determine the power of the electric engine starter in your car that draws 60 Amperes at 12 Volts
when you turn the ignition key.
4. One summer I installed some decorative low voltage lighting (15 volt) around my patio. The
lights are wired in parallel. The manufacturer says that the power supply can safely deliver a current
of 8 A. How many 18 Watt lights can be attached to a single power supply

5. Phones, answering machines, video cameras and other low voltage appliances can be plugged in
with a thin wire that has a big lump at the plug-in end. The lump is called a transformer and
"transforms" high voltage electricity into low voltage electricity. A common transformer has an
output of 350 milliamperes at 10 volts. How much current does this transformer need from your
120 Volt outlet (Assume that the power into the transformer equals the power out of the
transformer.)
6. Houses have current limiting devices such as fuses or circuit breakers to prevent too much
current from flowing through the house wiring. A typical fuse lets no more than 15 Amps flow in a
circuit. How many 100 Watt light bulbs could be safely lit on this circuit
7. A standard house circuit can handle a flow of 20 Amperes of electrical current at 120 Volts.
a. Determine the maximum wattage for the circuit.
b. Determine how much electrical energy is "used" when 20 A at 120 V flows for an hour.
c. Determine how much this hours' worth of energy would cost at 6 cents per kilowatt-hour.

8. Suppose you were using a shop vac to clean up the spillover from a flooded washing machine. If
the shop vac flipped over and flooded the motor with water, how might the grounding wire save
your life
9. After blow-drying your hair, you set the dryer on the edge of the sink and it slips into the sink,
full of water. How could the Ground Fault Circuit Interrupter save your life
10. When designing a home electrical system, why are the outlets and lights for a single room NOT
on a single circuit (What would happen if you overloaded the circuit)
11. If a 60 W light bulb and a 100 W light bulb are connected in series to a 120 V outlet, they are
not actually 60 W and 100 W bulbs. To show the difference:
a. Draw a circuit diagram for the bulbs in parallel, label the resistances and voltage drops and
determine the actual power of each bulb.
b. Draw a circuit diagram for the bulbs in series, label the resistances and voltage drops and
determine the actual power of each bulb.