• 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

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