Download OHM’S LAW

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Ohm’s Law
• The ratio of the potential difference to the
current in a metal conductor is a constant.
This is equal to the resistance.
R = V/I
R- resistance(Ω)
I- current (Amps)
V- Potential difference (V)
EXAMPLE
a) What is the resistance of a lamp that is
plugged into a 120V outlet and has a
current of 0.75Amp?
R = V/I = 120V / 0.75Amp
R= 160Ω
b) What is the power of the bulb?
P=VI = 120V(0.75Amp)
P = 90 Watts
Power and Work
P=VI = (IR)I = I2R
P = V(V/R) = V2/R
W = Pt = VIt = I2Rt = V2 t
R
*all on reference table
CIRCUIT SYMBOLS
Resistor
Variable
Resistor
Dry cell
Switch
Battery (DC
Source)
Generator (AC source)
Lamp
MORE SYMBOLS
Motor
Electrical
ground
Voltmeter- Measures drop in potential
across a resistance. (Placed in parallel)
Ammeter- measures current in the circuit
(placed in series)
Galvonometer- used to measure very small
amounts of current.
SIMPLE CIRCUIT
*You could also use a
resistance symbol for the lamp
When diagraming
 Always label values for voltage, current
and resistance.
Always show direction of current when a
battery is in the circuit.
Make sure you use the correct symbols
Example
A circuit contains a 60V battery, an ammeter, a
switch and a lamp of 30Ω. Draw a circuit diagram
and determine the reading on the ammeter.
R=30Ω
R= V/I
30Ω = 60V / I
V=60V
I = 2 Amp
I = 2Amp