Electric Power
Energy transfer rate in circuits and the relationships among power, voltage, and current
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Series, Parallel Differences
Show Me The Physics
School blocks YouTube? Download file below.
Show Me The Physics
III) Electric Power Power - time rate of doing work or expending energy
since V = W/q,
CROSS MULTIPLY then W = Vq
P = Vq/t
(All equations in reference table)
P = VI since V = IR …
THEN P = I2R
since I = V/R …
THEN P = V2/R
P = VI = I2R = V2/R P = W/t Giancoli p. 516) 11
a) R = 20. ohms
P = W/t = VI W = VIt = 12V[.60 A]60 sec
b) 430 J
Ex) Series circuit w/ two lamps, the battery supplies a potential difference of 1.5 volts. Current in the circuit is 0.10 ampere, what rate does the circuit use energy?
V = 1.5 V (rate of energy use)
P = VI = 1.5 V(.10 A)
P = .15 watts
or .15 VA
 Series Circuit Game - Flash [
HTML5 ]
P, R Relationship???? P = I2R = V2/R
Parallel Circuit, P = V2/R
P, R are inverse when
5 Ω would be brighter because it has less R
Review - Series or Parallel?
Dorling Kindersley Books
Parallel
Enrichment
AC Current - Tesla
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Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. Electric power is defined as:
2. A circuit has a 1.5 V battery and a current of 0.10 A. At what rate does it use energy?
3. A current of 2.0 A flows through a 5.0 Ω resistor. What power does it use?
4. A 6.0 Ω resistor has 12 V across it. What power does it use?
5. A 5 Ω and a 10 Ω bulb are connected in parallel. Which one uses more power?
Comparing Hair Dryers
A hair dryer is rated at 1500 W when connected to a 120-V outlet.
What current does the hair dryer draw?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
C2. Substitute numerical values into a mathematical representation that can be used to determine the resistance of the heating element while the dryer operates at 1500 W. Then calculate the resistance.
C3. The dryer’s “low” setting uses only 750 W at the same voltage. How does the element’s resistance on low compare with high?
C4. Determine the electrical energy the hair dryer uses when it runs at 1500 W for 10. minutes.
C5. A wire carrying current has a small resistance. If the current doubles, how does the power wasted as heat in the wire change?
C6. A manufacturer wants to sell a more powerful 1875-W dryer for the same 120-V outlets, which are usually protected by 15-A breakers. Identify one benefit and one drawback of this design. Support your drawback with a calculation.