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Electric motors - Higher - OCR 21st CenturyHow to calculate the force

Electromagnetism is caused by the magnetic fields around wires carrying an electric current. The induced magnetic field of a wire can interact with other nearby magnets, producing a force.

Part of Physics (Single Science)Electric circuits

How to calculate the force

To calculate the force on a wire carrying a current at right angles to a magnetic field, use the equation:

force on a conductor carrying a current = magnetic field strength 脳 current 脳 length

\(F = B ~ I ~ l\)

This is when:

  • force (F) is measured in newtons (N)
  • magnetic field strength (B) in measured in tesla (T)
  • current (\(I\)) is measured in amps (A)
  • length (l) is measured in metres (m)

Example

A 50 cm wire carries a current of 2 A. Calculate the force acting on the wire when it is placed at right angles in a 0.4 T magnetic field.

First convert the units:

\(50~cm = \frac{50}{100} = 0.5~m\)

Then substitute the values into the equation:

force on a conductor carrying a current = magnetic field strength 脳 current 脳 length

force = 0.4 脳 2 脳 0.5

force = 0.4 N

Question

A 5.0 cm wire carries a current of 0.75 A. Calculate the force acting on the wire when it is placed at right angles in a 0.60 T magnetic field.