III) Electric Power
Power - time rate of doing work or expending energy
| P = W/t | |
| (watts) | (J/seconds) |
since V = W/q,
CROSS MULTIPLY
then W = Vq
P = Vq/t
P = VI
(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
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?
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| a)15 W | b)1.5 W | d).15 W | c).015W |
V = 1.5 V
I = .10 Amps
P = ?
(rate of energy use)
P = VI = 1.5 V(.10 A)
P = .15 watts
or .15 VA
Series Circuit Game
St. Mary H.S. Physics
P, R Relationship????
P = I2R = V2/R
P,R direct when resistors have same current P = I2R P,R Inverse when resistors have same V P = V2/R |
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In which kind of circuit would a 5 Ω resistor be brighter (more power) than a 10 Ω resistor? Hint: P = V2/R and P = I2R
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Parallel Circuit, P = V2/R
P, R are inverse when
V is constant.
5 Ω would be brighter because it has less R
Electric Energy and Heat
(W) Electric energy consumed or released as heat
(All equations on reference table)
(J) W =
Pt = [V2/R]t
= VIt =
I2Rt
| An electric iron operating at 120 volts draws 10. amperes of current. How much heat energy is delivered by the iron in 30. seconds? |
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| a) 1.2 x 103 J | c) 3.6 x 104 J |
| b) 3.0 x 102 J | d) 3.6 x 103 J |
V = 120 V
I = 10. A
t = 30. sec
W = ?
W = VIt
= 120. V(10. A)(30. sec)
W = 3.6 x 104 J
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What's wrong with this picture?
Ammeter should be |
St. Mary's H.S. Animations
Circuits - Series and Parallel
Scientific Advisors: Dr. Saul Dushman; Dr. Roman
Smoluchowski; Dr. David Harker
Prelinger
Archives
Production Company: Wolff (Raphael G.) Studios, Inc.
Audio/Visual:
sound, color
Creative Commons license:
Public Domain
Electricity Unit Review