2. Resistance
How much energy does it take to push a coulomb of charge across a filament?
Defined as the ratio of POTENTIAL DIFFERENCE across the LOAD
POTENTIAL DIFFERENCE = VOLTAGE (V)
LOAD = CURRENT (I) V
R = I
Voltage
Resistance =
Current

3. Units of Resistance Units of Resistance are called OHMS
Named in honour of Georg Simon Ohm
The symbol for Ohms is the greek letter OMEGA (Ω)
Ohm was the first to publish results of various resistances on types of wires

4. Georg Ohm’s Findings Ohm took various types of conductors
Applied a current across the wire
No matter what the Potential Difference (Voltage) --- the Resistance was the same
Called Ohm’s Law

5. Ohm’s Law V = IR Voltage = Current x Resistance

6. Model Problem
What is the resistance of the heating coil of an electric heater if a current of 12.5 A runs through it?
I = 12.5 A
V = 120 V
R = V / I
R = 120 / 12.5
R = 9.6 V / A
R = 9.6 Ω

7. Wasting Energy
Do resistors have to convert energy to a different source?
Can be used to control the current or Potential difference at different points in the circuit.

8. Measuring Resistance What is the Resistance? R = V / I V = 6 I = 3
3 Amps
Potential Difference = 6