Electric Circuits

Electric Power

Energy transfer rate in circuits and the relationships among power, voltage, and current

 

Electric Power lesson illustration

Review - Series or Parallel?

image of Parallel circuit

Dorling Kindersley Books

 

Series, Parallel Differences

Show Me The Physics
YouTube Channel

School blocks YouTube? Download file below.

SeriesParallel_Diff_YT.MOV

 

 

 Electric Power lesson illustration

 

Fill in the Blank Notes

 

Show Me The Physics
YouTube Channel

 

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)

 

Electric Power lesson illustration

 

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

 

 

Electric Power lesson illustration

 

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?

Electric Power lesson illustration
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

 

 

Electric Power lesson illustration

 

 


Electric Power lesson illustration

Series Circuit Game - Flash

[ HTML5 ]
Show Me The Physics Website

 

Electric Power lesson illustration

 

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

 

 

Enrichment

Electric Power lesson illustration

AC Current - Tesla

Nikola Tesla - Mad Electricity part 3 of 5
 - History Channel

 

 

 

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?

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