# Topic 5 Magnetic Fields Notes

This is a sample of our (approximately) 4 page long Topic 5 Magnetic Fields notes, which we sell as part of the AQA PHYA4 - Fields and Further Mechanics Notes collection, a A* package written at Bishop Vesey'S Grammar School in 2014 that contains (approximately) 16 pages of notes across 5 different documents.

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### Topic 5 Magnetic Fields Revision

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Topic 5: Magnetic Fields 1

Current carrying conductors in magnetic fields a Magnetic flux density is the magnetic force per unit length per unit current on a current-carrying conductor placed perpendicular to the magnetic field lines i A Tesla is the magnetic flux density if a 1m length of wire carrying a current of 1A experiences a magnetic force of 1N, when placed in the field in such that the current flows perpendicular to the magnetic field lines b Current-carrying wires in a magnetic field will experience a force perpendicular to the field lines and to the flow of the current:

F=BIl i

c

2

Force is greatest when current flows perpendicular to the field lines ii Force is weakest when current flows parallel to the field lines Fleming's left hand rule for motors i Thumb = motion ii First finger = field lines iii Second finger = conventional current

Moving charges in magnetic fields a Moving charges in a magnetic field will experience a force perpendicular to the field lines and to the flow of the current:

F=BQv i

b

Force is greatest when velocity is perpendicular to the field lines ii Force is weakest when velocity is parallel to the field lines Uniform magnetic fields: Circular motion (F=BQv) i Due to Fleming's Left Hand rule, the magnetic force acts at right angles to the direction of motion of the electron ii As F=BQv, the magnitude of the magnitude force will remain constant but as the magnetic force remains at right angles to the direction of motion, even when there is a change of direction, the magnetic force is a centripetal force iii As a result, the path of the charge will be circular and the radius of the circular path will be

r=
c

mv BQ

Uniform electric fields: Parabolic motion (F=EQ) i Due to the potential difference between the plates, the electric force will act downwards ii As a result, the electric force increases the charge's vertical component of velocity but leaves the charge's horizontal

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