A2 Physics-Electric and Magnetic Fields

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Unit 4-Physics On The Move
Topic 2-Electric and Magnetic Fields
Explain what is meant by an electric field and recognise and use
F
the expression for electric field strength E= Q


Charges and fields
Electric charge is one of the fundamental properties of nature. Two objects of the same charge…

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kQ1Q2 1
Use the expression F= r² where k= 4 and derive and use the
kQ
expression E= r² for the electric field due to a point charge
kQ1Q2
The electrostatic force between two charges spherical objects obeys an inverse square law: F= r²
, where Q and Q are…

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Capacitance
Any arrangement of two conductors isolated from one another by an insulator will form a capacitor.
In the lab this may be two sheets of metal with small pieces of plastic between. In this case air forms
the insulator. A commercial capacitor can be made by using sheets of…

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the wires). Surprisingly, the uncharged capacitor does not resist the current arriving at one plate or
leaving the other. On a graph of capacitor charge against time, the initial current is the gradient of the
graph at the origin. As charge build up on the plates, it repels more charge…

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Lines representing the magnetic field in a given region are called `lines of magnetic flux'. The number
of lines passing through a unit area perpendicular to the field represents the flux density, B, and is a
measure of the magnetic field strength.

The e.m.f. induced in a circuit can be…

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This is also the direction in which the magnetic force would act on a `free north pole' if
monopoles existed
In the case of the field round the long wire, the sense is determined by the direction of the
current in the wire


Force between two current-carrying wires
If the…

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of the torque changes, so the rotation is not smooth. The size of the torque on the coil can be
increased by

Increasing the area of the coil
Increasing the current in the coil
Using more turns of wire in the coil
Using a stronger magnetic field
Making the magnetic…

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is not at 90° to the magnetic field lines, then the angle between the path and the field lines must also
be taken into account.


Magnetically induced electric currents
The magnetic force on a moving charge can be used as a means of generating an electrical current.
Any piece of…

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bundled together or iron dust packed into the core. Very high-frequency transformers use cores
made from non-conducting but magnetic materials, such as ferrites. These materials are similar to
ceramics, and so can be quite brittle, and are far less easily magnetised than soft iron.
d(N )
Investigate, recognise and use…

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