A current-carrying conductor (i.e. any wire within a complete circuit) experiences a force when placed in a magnetic field due to its own magnetism. This is called the motor effect.
We use Fleming's left hand rule to find out the correct direction of force.
Key Concepts
Use quizzes to practise application of theory.
START QUIZ!
The diagram shows a conductor in a magnetic field
The direction of the force experienced by the wire is
FLHR
The diagram shows a conductor in a magnetic field
The direction of the force is
FLHR
This diagram represents a wire next to a magnet
The direction of the force experienced by the wire will be
The B field goes from N to S, then FLHR
The diagram represents a wire in a circular B field
The direction of force on the wire will be.
The direction of field is at a tangent to the circle (up), then FLHR
The diagram shows a current carrying conductor close to a magnet
The direction of the force on the magnet is:
B field goes from N to South so to the right. FLHR gives force on wire up so force on magnet is down (Newt 3)
A 20 cm long conductor is situated in a perpendicular magnetic field of flux density 5 mT. If the current flowing through the conductor is 3 A the force experienced will be.
20 cm = 0.2 N
5 mT = 0.005 T
F = BIL
A conductor experience a force of 0.02 N per meter in a 5 mT perpendicular field. The current flowing through the conductor is.
I = F/BL = (F/l) /B
Two wires are arranged perpendicular to each other as shown.
The direction of the force on the top wire will be:
The field due to the lower wire will be parallel to the top one so, no force
Two parallel current carrying conductors are placed next to each other as shown.
The direction of the B field cutting the red wire is
Use the grip rule on the blue one. The field experienced by the red one is at a tangent to the circle.
A current flows clockwise around a rigid square coil of wire placed in a magnetic field as shown.
The wire will
Each side will experience a force outwards from the centre. These will be balanced
A red current carrying conductor is placed in a B field as shown. An identical blue conductor carrying the same current is placed above it.
If the force experience by the red one is F the the force experienced by the blue one will be
F = BIL cos (angle between normal and field)
How much of Force on a current-carrying conductor have you understood?
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