# 7.2.2 The Motor Effect

Higher Tier Only

### The Motor Effect

• The motor effect occurs:

When a wire with current flowing through it is placed in a magnetic field and experiences a force

• This effect is a result of two interacting magnetic fields
• One is produced around the wire due to the current flowing through it
• The second is the magnetic field into which the wire is placed, for example, between two magnets
• As a result of the interactions of the two magnetic fields, the wire will experience a force The magnetic field between opposite poles of magnets interact with the magnetic field produced around a current-carrying wire The motor effect is a result of two magnetic fields interacting to produce a force on the wire

#### Factors Affecting Force

• The size of the force exerted by the magnetic fields can be increased by:
• Increasing the amount of current flowing through the wire
• This will increase the magnetic field around the wire
• Using stronger magnets
• This will increase the magnetic field between the poles of the magnet
• Placing the wire at 90o to the direction of the magnetic field lines between the poles of the magnet
• This will result in the maximum interaction between the two magnetic fields
• Note: If the two magnetic fields are parallel there will be no interaction between the two magnetic fields and therefore no force produced
Higher Tier Only

### Calculating Magnetic Force on a Current-Carrying Conductor

• The size of the force acting on a current-carrying wire in a magnetic field can be calculated using the equation:

F = BIL

• Where:
• F = force acting on current-carrying wire in Newtons (N)
• B = magnetic flux density (which is the strength of the magnetic field) in Tesla (T)
• I = current flowing through the conductor in Amps (A)
• L = length of the conductor that is in the magnetic field in metres (m) Force on a current carrying conductor (directed into the page)

#### Worked Example

A 5 cm length of wire is at 90o to the direction of an external magnetic field. When current of 1.5 A flows through the wire it experiences a force of 0.06 N from the motor effect.

Calculate the magnetic flux density of the magnet.  ### Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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