# G485 Revision Notes

Complete set of revision notes for OCR A G485 exam.

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OCR (A) PHYSICS

G485

Revision
Notes

Electric Fields

Electric Field Strength

A charged object is surrounded by an electric field, if a charged particle enters this
electric field it will experience a force. The magnitude of this force depends on the
charge on the particle and the strength of the…

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Electric Field Patterns

Electric field patterns can be shown using electric field lines. The direction of the
field shows the direction of the force experienced by a small positive charge
placed at that point. This is why electric field lines always point away from positively
charged objects and towards negatively…

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The potential difference between the plates is V
and the plates are separated by a distance d. If a
positive charge, Q, is moved from the negative
plate to the positive plate at a constant velocity
then:

Work done on the charge = energy
transformed

F x d = V…

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0 is known as the permittivity of free space.

Coulomb's law can also be applied to uniformly charged spheres providing you
measure the distance r from the centre of the spheres as if the charges were
concentrated there.

Electric Field Strength for a Radial Field

Electric field strength is equal…

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Magnetic field lines can also be mapped out using magnetic field lines. The
direction of the field in this case shows the direction of the force experienced by a
free moving north pole at that point. Hence magnetic field lines will always point
towards a south pole and away from…

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Fleming's Left Hand (Motor) Rule

Magnets that are placed close together experience a force because their fields
interact.

A current carrying wire therefore experiences a force when placed in an external
magnetic field because the two fields interact. The direction of this force can be
determined using Fleming's left hand…

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The magnetic flux density is 1T when a wire carrying a current of 1A placed at
right angles to the field experiences a force of 1N per metre of its length.

1T is therefore equal to 1Nm-1A-1

This equation can be rearranged to find the magnitude of the force on…

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magnetic fields are arranged so that the electrical force on the particle is in the
opposite direction to the magnetic force.
For the charged particles travelling in
a straight line from one end to the
other the magnetic force is equal
to the electric force. Hence:

EQ = BQv

The…

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These 3 quantities sound very similar but have different meanings and are very
important when dealing with electromagnetism:
1. Magnetic flux density, B
2. Magnetic flux,

Magnetic flux, ,
is defined by the following equation:

Magnetic flux = magnetic flux density x cross sectional area normal…

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There are 3 ways in which an e.m.f. may be induced in a circuit:
1. Change the magnetic flux density (B) ­ i.e. move a coil closer to the
magnet
2. Change the area (A) of the circuit ­ i.e. move a straight wire at right angles to
the field…