St. Mary's H.S. Physics - Electric Power

Series, Parallel Differences

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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?


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

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

Parallel Circuit, P = V²/R

P, R are inverse when
V is constant.

5 Ω would be brighter because it has less R

Review - Series or Parallel?

image of Parallel circuit

Dorling Kindersley Books

Parallel

Electric Energy

Enrichment

AC Current - Tesla