G485 Electric and magnetic fields

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  • Created by: Madeleine
  • Created on: 29-05-13 11:11
How are electric fields created?
By electric charges
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Define Electric Field Strength, E
The force experienced per unit positive charge
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Which direction do electric field lines travel?
Away from positively charged particles towards negatively charged particles
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What is Coulomb's law?
Two point charges exert an electrical force on each other which is directly proportional to the product of the charges and inversely proportional to the square of the separation between the charges
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How is a uniform electric field created?
Using two oppositely charged parallel plates produces an electric field strength which is constant
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How do charged particles move in an electric field?
They would follow a parabolic trajectory (curve)
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Similarities of an electric field to a gravitational field:
Field strengths follow an inverse square law with distance, a point mass and a point charge both produce a radial field, field strength is defined as force per unit mass/positive charge
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Differences between an electric field and a gravitational field:
Electric field is created by a charge whilst gravitational fields are created by mass, electric fields can be attractive or repulsive and gravitational fields are only attractive
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Describe the magnetic field pattern of a long straight current carrying conductor (wire):
The field circles the wire, the field strength is strongest near the wire and the strength decreases with distance from the wire. Right hand with your thumb extended in the direction of the current, your fingers show the direction of the field lines.
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Describe the magnetic field of a long solenoid:
The field is uniform within the solenoid. Outside the coil the field is similar to that produced by a bar magnet.
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State Fleming's left-hand rule
If the thumb, index and middle finger are extended at right-angles to each other, lining your index finger with the direction of the field and your middle finger with the current your thumb will show the direction of the force experienced on the wire
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Define magnetic flux density, B
B=F/(ILsinA) where F is the force on a wire of length L carrying a current I at an angle A to the field
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Define the tesla, T
One tesla is the magnetic flux density when a wire of length one metre and carrying a current of one ampere at 90 degrees to the field experiences a force of one newton.
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A charged particle moving in a plane perpendicular to a uniform magnetic field...
moves in a circular orbit and the magnetic force can be related to the centripetal force
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How does a mass spectrometer work?
Charged ions are travelling in a vacuum and velocity selector, the ions which leave the velocity selector will have speed v=E/B1 where B1 is the magnetic flux density in the velocity selector. The ions then enter a uniform magnetic field of B2,
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Mass spec contd.
in this field the ions will travel in a circular path. The radius of this path will be given by r=mv/(B2Q) and substituting v=E/B1 in you get r=mE/(QB1B2) by measuring r with a detector the ions mass can be found.
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Define magnetic flux, (circle with line through it)
The product of the magnetic flux density and the area through which it travels.
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Define the weber, Wb
One weber is the magnetic flux when a magnetic field of magnetic flux density 1 tesla passes through an area of one square metre.
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Define magnetic flux linkage
For a coil equals the magnetic flux through the coil multiplied by the number of turns on the coil.
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State Faraday's law of electromagnetic induction
The magnitude of the induced e.m.f is equal to the rate at which magnetic flux is cut
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State Lenz's law
The direction of any induced current is in a direction that opposes the flux change that causes it.
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Describe an a.c. generator
Rotating a coil in a constant magnetic field will produce an alternating current.
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Describe a transformer
Two coils of insulated copper wire wound on top of one another on a core of easily magnetised iron. The primary coil is the coil connected to the a.c. input, the secondary coil is connected to the output. The core is normally a complete loop of iron.
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Describe a step-up transformers function
They increase the e.m.f. of the output
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Describe a step-down transformer
They decrease the e.m.f of the output
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Other cards in this set

Card 2

Front

Define Electric Field Strength, E

Back

The force experienced per unit positive charge

Card 3

Front

Which direction do electric field lines travel?

Back

Preview of the front of card 3

Card 4

Front

What is Coulomb's law?

Back

Preview of the front of card 4

Card 5

Front

How is a uniform electric field created?

Back

Preview of the front of card 5
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