G485 Revision Notes

Complete set of revision notes for OCR A G485 exam.

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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 field. Therefore electric field strength
at a point is defined as:
The electric field strength, E, at a point is the force experienced per unit
charge exerted on a positive charge placed at that point.
E = F/Q
F is the force experienced by a charge of Q.
The unit is NC-1 and electric field strength is a vector, it has both magnitude and
Annabel Davies G485 Revision Notes

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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 charged ones.
All electric fields are created by fundamental particles such as protons and
electrons. These single particles produce a radial electric field.…read more

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The potential difference between the plates is V
and the plates are separated by a distance d.…read more

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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 to F/Q. So, substituting Coulomb's Law in for F gives:
E = (Qq/40r2)/q
E = Q/40r2 as the two q cancel out.…read more

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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 a north pole as shown below.
Moving charges create a magnetic field, therefore when the charges stop moving
the field disappears.…read more

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Fleming's Left Hand (Motor) Rule
Magnets that are placed close together experience a force because their fields
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 rule if the wire is placed perpendicular to
the magnetic field.
In this, the direction of the motion
experienced by the wire (the force) is
given by the thumb.…read more

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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 a current
carrying wire placed in an external magnetic field. Hence:
F = BILsin
NOTE: when is equal to 90 sin is equal to 1 and can therefore be ignored.…read more

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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 charge on the particle cancels
out and the equation becomes:
v = E/B
Charged particles with speeds other
than that given by this equation are deflected and will miss the slit at the other end
of the velocity selector.…read more

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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,
3.…read more

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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
2. Change the area (A) of the circuit ­ i.e. move a straight wire at right angles to
the field
3. Change the angle ( )­ i.e. rotate the coil as in a generator
The direction of this induced e.m.f.…read more


Seren Thomas

These are great! Thanks for putting these up :) x

Always J

Thanks for uploading!!!! So complete and useful!!!

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