Resistance (Edexcel IGCSE Physics)

• Resistance is defined as the opposition to current:
  • The higher the resistance of a circuit, the lower the current
  • This means that good conductors have a low resistance and insulators have a high resistance

• The symbol for resistance is R
• It is measured in Ohms (Ω)
  • Ω is the Greek capital letter ‘Omega’
  • An Ohm is defined as one volt per ampere (1 V / A)

• The resistance of a circuit can be increased by adding resistors (or variable resistors) to it
• Every electrical component has a resistance, even wires
  • In exam questions, the resistance of the wires and batteries are assumed to be negligible

High resistance means there is a lower current and vice versa

• The current I through a component depends on both the resistance R of the component and the potential difference V across the component
  • The greater the resistance R of the component, the lower the current I for a given potential difference V across the component
  • The lower the resistance R of the component, the greater the current I for a given potential difference V across the component

• The current, resistance and potential difference of a component in a circuit are calculated using the equation:

• This equation can be rearranged with the help of the following formula triangle:

Voltage, current, resistance formula triangle

Step 1: List the known quantities

• • Resistance, R = 10 Ω
  • Current, I = 0.3 A

Step 2: Write the equation relating resistance, potential difference and current

V = IR

Step 3: Substitute in the values

V = 0.3 × 10 = 3 V