Resistance and Calculating Resistance in Circuits

Key Concepts

• Electricity and Energy Transfer

  • Electricity involves the transfer of energy in a circuit.
  • Chemical Energy: Stored in a cell, transformed into electrical energy.
  • Current: Flow of electrons around the circuit, carrying energy.
  • Energy Conversion: When electrons pass through a component (e.g., a lamp), electrical energy converts into light and thermal energy.

• Potential Difference (Voltage)

  • Used to calculate energy transfers in a circuit.
  • Example: A cell with 9 volts supplies 9 joules of energy per coulomb of charge.
  • The potential difference across a component, like a lamp, indicates energy transferred.

Resistance

• Definition:

  • Resistance indicates the potential difference required to drive a current through a component.
  • Higher resistance means more energy is needed to drive the current.

• Electron Collision:

  • Electrons moving through a conductor (e.g., metal wire) collide with atoms, transferring electrical energy into other forms, mainly thermal.

Calculating Resistance

• Formula:

  • ( \text{Resistance (ohms)} = \frac{\text{Potential Difference (volts)}}{\text{Current (amperes)}} )
  • Unit: Ohm (Ω)

• Example Calculation:

  • Lamp A:
    • Current: 1 ampere
    • Potential Difference: 1 volt
    • Resistance: 1 ohm
  • Lamp B:
    • Current: 1 ampere
    • Potential Difference: 10 volts
    • Resistance: 10 ohms

Rearranging the Equation

• To find potential difference:

  • ( \text{Potential Difference (volts)} = \text{Current (amperes)} \times \text{Resistance (ohms)} )

• Example:

  • Calculate Potential Difference:
    • Current: 0.5 amperes
    • Resistance: 50 ohms
    • Calculation: 0.5 × 50 = 25 volts

Additional Resources

• For more practice, consult the revision workbook available via the provided link.

By the end of this topic, you should understand the concept of resistance and how to calculate it in electrical circuits.