2) Resistance and V = IR

1. Formula for Potential Difference, Current, and Resistance

  • Ohm’s Law: V=I×R

    • V = Potential difference (volts, V)

    • I = Current (amperes, A)

    • R = Resistance (ohms, Ω)

  • Formula Triangle: Cover the variable you’re solving for to easily rearrange the equation.

2. Example Problem Using Ohm’s Law

  • Example: A resistor with R= 4.0 Ω and V=6.0 

    • Solution: I= V/R =6.0 V / 4.0 Ω= 1.5 A

3. Factors Affecting Resistance

  • Resistance changes based on:

    • Circuit Type: Series vs. parallel (affects total resistance).

    • Wire Length: Longer wires increase resistance.

    • Wire Diameter and Material: Thinner wires and specific materials also affect resistance.

4. Practical Investigation: Effect of Wire Length on Resistance

  • Equipment: Ammeter, voltmeter, ruler, crocodile clips, and a thin test wire.

  • Method:

    1. Set up a circuit with the wire, ammeter in series, and voltmeter across the wire.

    2. Start with one clip at 0 cm and another at a specific length (e.g., 10 cm).

    3. Record current (A) and potential difference (V) for each length.

    4. Move the clip to a new length (in steps of 10 cm) and repeat.

  • Calculations:

    • Use R=V / I to find resistance at each length.

  • Graph:

    • Plot resistance (y-axis) vs. length (x-axis).

    • A straight line through the origin indicates that resistance is proportional to length.

  • Note: Allow the wire to cool between readings to avoid heating effects.