Motor Effect

This lesson covers:

  1. The idea that a current-carrying wire will experience a force if placed within a magnetic field
  2. How to find the direction of the force using Fleming's left hand rule
  3. How to find the strength of the force using the equation: F=BILF=BIL

motor / engine / current


A carrying wire in the presence of a magnetic field will experience a force. This is called the effect.

current
motor

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2

parallel / perpendicular


To experience the full force, a current carrying wire must be placed to the magnetic field.

perpendicular

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1

Diagram showing Fleming's left hand rule with directions for current, force, and magnetic field labeled A, B, and C.

Fleming's left hand rule can be used to tell us the direction of the force experienced by a current carrying wire in a magnetic field.


In the diagram above, match the letters A to C with what they represent in Fleming's left hand rule:


Direction of the current:

Direction of the force:

Direction of the magnetic field:

C
A
B

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Diagram showing Fleming's left hand rule to find the direction of force experienced by a wire between two magnets.

Use Fleming's left hand rule to find the direction of the force experienced by the wire.


The force is:

Downwards

Upwards

To the right

To the left

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The force (F) experienced by the wire is determined by:


  1. The current (I) in the wire
  2. The magnetic field strength (B). This is also called magnetic flux density.
  3. The length (L) of the wire that crosses the magnetic field.


The formula to calculate the force is:

(Note: this formula is given to you in the exam)

F=BILF=\frac{B}{IL}

F=IBLF=\frac{I}{BL}

F=BILF=BIL

F=BILF=\frac{BI}{L}

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The magnetic field strength (also known as magnetic flux density) is measured in:

Coulombs (C)

Amperes (A)

Volts (V)

Teslas (T)

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Diagram showing a wire carrying a current of 2 A perpendicular to a magnetic field of 15 T with a length of 0.2 m.

A wire carrying a current of 2 A is perpendicular to a magnetic field of 15 T.


The length of the wire in the field is 0.2 m.


What is the force experienced by the wire?

6

N

N

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Diagram showing a wire carrying a current of 6 A perpendicular to a magnetic field of 30 T with a length of 0.1 m.

A wire carrying a current of 6 A is perpendicular to a magnetic field of 30 T.


The length of the wire in the field is 0.1 m.


What is the force experienced by the wire?

18

N

N

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1