V

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)

EXAMPLEa) 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 VariableResistor

Battery (DC Source)

SwitchDry cell

Generator (AC source)Lamp

MORE SYMBOLS

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.

Motor Electrical ground

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

V=60V

R= V/I

30Ω = 60V / I

I = 2Amp

I = 2 Amp