Transcript Rates of Charge Flow and Energy Transfer

Current Electricity
Current and Circuits
Producing Electricity:
electric current
conventional current
battery
photovoltaic
Electric Circuits
A closed loop of
conductors…………………..
Rates of Charge Flow and Energy Transfer
Ampere
Power
P = IV
Resistance and Ohm’s law
Resistance
R=V/I
V
I
R
Problem Solving Strategies
1. Draw battery on left side of page with + on
top.
2. Draw the wire coming out of the positive
terminal to the next device.
3. Follow the current path until you reach the
negative terminal.
4. Check your work !
Using Electric Energy
•Heating a Resistor
•Recall: P = VI and V = IR
Substituting: P = I2R
The power dissipated by a resistor is
proportional to the square of the current
that passes through it and its resistance.
E = Pt
E=
2
I Rt
•Transmission of Electric Energy
Thermal energy is at a rate represented by
P = I2R
Even the wires carrying the electricity from the power
plant lose energy through thermal loss.
•Reduce through lower R
•Reduce through lower I
This can be accomplished in several
ways:
•We can lower “R” by increasing the size of the
cables.
Advantages?
Disadvantages?
•We can lower “I” by increasing the voltage and
delivering the same amount of power.
Advantages?
Disadvantages?
•The Kilowatt - Hour
Electric energy used is measured as a rate of energy
consumption in joules per second (watts) times the number
of seconds it is operated.
Ws
or
Js/s =J
1 kWh = (1000j/s)(3600s) = 3.6 X 106 J