Download Electric Circuits - Physics-with-T

Electric Circuits
Watts
• Power is measured in watts (just like
in motion)
• In electricity, Watts = Volts * Amps
– P = V*I
• Power is a measure of the rate at
which electricity does work or
provides energy
Energy
• Just like motion, energy is
measured in Joules
• Energy = Power * Time
– 1 Joule = 1 watt * 1 second
– Your parents are billed for the energy
used in kilowatt hours
Parallel vs. Series
• Compare the circuit to a river –
think about what happens to the
current, resistance, and pressure
(volts)
Series
• Volts get decreased (used) by each
item in the circuit until all voltage is
used up
• Current is constant – like the river
• Resistance simply adds up to get
total resistance
Parallel
• Voltage is constant
• Current is divided between branches
of the circuit – like the river
• Total resistance is less because fewer
electrons (current) need to go
through the individual resistance
Parallel Circuit Resistance
• To find the total resistance of a
parallel circuit
– 1/Rt = 1/R1 + 1/R2 + . . .
– Rtotal = 1/R1 + 1/R2 + . . .
– Rt = 1/Rtotal
Sample Parallel Circuit
3
Rtotal = 1/R1 + 1/R2 + . . .
3
Rtotal = 1/3 + 1/3 + 1/3
Rtotal = 1
3
Rt = 1/Rtotal
Rt = 1/1
Sample Parallel Circuit
4
Rtotal = 1/R1 + 1/R2 + . . .
4
Rtotal = 1/4 + 1/4 + 1/4
Rtotal = .75
4
Rt = 1/Rtotal
Rt = 1/.75
Rt =1.33