Electric Energy
Electrical energy use, kilowatt-hours, cost, and efficiency
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Try this at Home!
Series or Parallel?
June 2003 Question 63
Answer - Parallel - same V
(W) Electric energy consumed or released as heat (All equations on reference table) (J) W =
Pt = [V2/R]t
V = 120 V I = 10. A t = 30. sec W = ? W = VIt = 120. V(10. A)(30. sec)
W = 3.6 x 104 J
Show Me The Physics
Circuits - Series and Parallel
Electricity Unit Review
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Electric Energy and Heat
Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. Which unit is used for electric energy in the equation W = VIt?
2. An electric iron at 120 V draws 10. A. How much heat energy does it deliver in 30. s?
3. A 100. W light bulb is on for 60. s. How much electrical energy does it use?
4. A current of 2.0 A flows through a 10. Ω heater for 5.0 s. How much energy is released as heat?
5. A toaster runs at the same power for twice as long. The electric energy it uses:
Reading the Electric Bill
A family runs a 1500-W space heater for 4.0 hours each evening. Their utility charges $0.15 per kilowatt-hour.
How much does it cost to run the heater for one evening?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. What kind of quantity is a kilowatt-hour?
C2. Substitute numerical values into a mathematical representation that can be used to determine the electrical energy, in joules, that the heater uses in one evening. Then calculate the energy.
C3. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
C4. Replacing the space heater with a heat pump that uses 500. W for the same heating would save how much each evening?
C5. Determine the cost of running the 1500-W heater for 4.0 hours every evening for a 30-day month.
C6. The family is deciding whether to replace the space heater with a heat pump that uses 500. W for the same heating. Identify one benefit and one drawback of making this change.