Resistance (OCR A Level Physics)

• Resistance is defined as the opposition to current
  • For a given potential difference: The higher the resistance the lower the current

• Wires are often made from copper because copper has a low electrical resistance
  • Materials with low resistance are known as good conductors

• The resistance R of a conductor is defined as the ratio of the potential difference V across to the current I in it

• Resistance is measured in Ohms (Ω)
  • Ω is the Greek capital letter 'Omega'
  • An Ohm is defined as one volt per ampere (1 V A^-1)

• The resistance controls the size of the current in a circuit
  • A higher resistance means a smaller current
  • A lower resistance means a larger current

• All electrical components, including wires, have some value of resistance

Step 1: List the known quantities

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

Step 2: Write the resistance equation 

Step 3: Rearrange for V

V = IR

Step 4: Substitute in the values

V = 0.3 × 10 = 3 V