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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

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) A series circuit contains two lamps and  a battery with a potential difference of 1.5 volts. If the current in the circuit is 0.10 ampere, at what rate does the circuit use energy? 

 

 

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 - Flash

[ HTML5 ]
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

 

 

 

 


AP Physics

 

p. 517) 33, 35, 37


 

 

 

Electric Energy

 

 

Enrichment

AC Current - Tesla

 

 

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