1. Resistance in Circuits

2. What is Resistance?
Electrical Resistance – the opposition to the movement of electrons as they flow through a circuit.
A resistor is a device placed in a circuit which reduces the flow of electrons.
The symbol for resistance is R
The unit of measure for resistance is the Ohm (Ω)

3. Internal resistance refers to how easily a material lets electrons flow through.
What materials would have high internal resistance?
What materials would have low internal resistance?

4. Factors that Affect Resistance
All materials have some internal resistance.
The greater the resistance, the lower the current and the material becomes warmer.
This occurs because electrons bump into the atoms in the material creating thermal energy.

5. There are 4 main factors which affect resistance:
Type of Material – conductor vs insulator
Cross-Sectional Area – thin vs thick wires
Length – regular cords vs extension cords
Temperature – warm vs cooler objects

6. Measuring Resistance Resistance can be measured using an ohmmeter.
However, German physicist Georg Ohm discovered a relationship between resistance, voltage and current, he called this Ohm’s Law.
Ohm’s law makes sure that the resistance in an electrical load is correctly matched to the energy source in order to avoid a short circuit.

7. Ohm’s Law Equation
Potential Difference (voltage drop) = Electrical Current x Electrical Resistance
Quantity
Symbol
Measured in:
Potential Difference (voltage) V
Volts (V)
Electrical Current I
Amperes (A)
Resistance R
Ohms (Ω)

8. Practice Problem:
If you have a 3V battery and a 1.5Ω light bulb, what will the current be? Show all your work.