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

 

Electric Energy and Heat

 

(W) Electric energy consumed or released as heat

 

All equations in 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?

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

 

 

 

 

What's wrong with this picture?

 

 

Ammeter should be
 in series with resistor

 

 

St. Mary's H.S. Animations

 

Electrons & Conductivity

Resistance in a Wire

Attaching Meters

Ohms Law - V & I

Circuits - Series and Parallel

Circuits & Total Resistance

Series Circuit Game

Parallel Circuit Game

 

 

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