Transcript Equivalent Resistance con’t - Forestville Middle

Chapters 17/18 Circuits Unit
Electrical Power
Electrical Energy
Kirchoff’s Rules
Electrical Power
Power is the rate at which work is done
In mechanics
P =
For Electrical Power
W
t
P = VI = I2R
V2
=
R
To get max power, would you make a series or parallel
circuit? Why?
Power Example
A potential drop of 50 volts is measured across a
250  resistor. What is the power developed in
the resistor?
Power Example #2
Which circuit uses the greatest power?
Think about this…
V2
P =
R
Electrical Energy
The amount of electrical energy used is
equal to the work done on an electrical
component
For mechanics: W = Fd
For electrical energy:
V2t
w = Pt = VIt = I2Rt = R
Electrical Energy Example
An Electrical heater draws a current of 8 amps and has a
resistance of 15 . How much energy does the heater
use in 1 minute?
Kirchhoff's First Law
The algebraic sum of the currents flowing through a
junction is zero.
Generally speaking, it says, the total current entering a
junction must equal the total current leaving the junction.
10A
20A
3A
??
Kirchhoff's Second Law
The algebraic sum of the potential differences in a circuit
loop must be zero.
Generally speaking, it says, around any loop in a circuit,
the voltage rises must equal the voltage drops
Junction Practice Problem
How much current must
be flowing out the other wire?
10 A
6A