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Physics > Electromagnetism > Flashcards

Electromagnetism Flashcards

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1
Q

Electric field

A

A force experienced by a charge due to an electric field

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2
Q

Electric fields between parallel plates

A
  • Plates produce uniform electric field throughout the plate
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3
Q

Work in electric fields

A

w = Fd = Vq = 0.5mv^2

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4
Q

Effect of a charged particle in a Magnetic field

A

F = qvBsin@

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5
Q

Right Hand Push Rule

A

Thumb - Direction of conventional current (Proton’s velocity)
Fingers - Direction of magnetic field
Palm - Direction of force

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6
Q

Motor Effect

A
  • When a current-carrying conductor is placed in a magnetic field, it experiences a force
  • A moving charge with a constant velocity produces a magnetic field
  • Electrons move as a stream in conductor with uniform velocity and produces a magnetic field surrounding the conductor

F = BIlsin@

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7
Q

Magnetic flux

A

A measure of the total magnetic field that passes through a particular area
- Faraday demonstrated that a change in magnetic field would result in an induced electromotive
% = BA cos@

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8
Q

Lenz’s law

A

An induced EMF always gives rise to a current whose magnetic field will oppose the original change in flux

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9
Q

Eddy currents

A

Special type of current that is induced when a metal plate experiences a change in magnetic flux

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10
Q

AC current

A
  • Function by mutual induction where a changing current in one coil causes an induced EMF in the area of another coil
  • AC current fed into primary coil. induces current in secondary
  • AC current switches periodically to maintain changing magnetic field
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11
Q

Step-up Transformers

A

Increases secondary voltage compared to primary voltage

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12
Q

Step-down Transformers

A

Decreases secondary voltage compared to primary voltage

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13
Q

Power Loss in Transmission Lines

A

The resistance in the transmission lines causes an inefficient transfer of energy when the electrical energy transmitted is eventually transformed into heat energy
- To reduce: current must be reduced before entering the transmission lines

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14
Q

Limitations of Transformers

A
  • Resistive heat production
    Iron core experiences change in flux
  • Eddy currents induced
  • Eddy currents in the iron core generates a significant amount of heat energy via resistance. Iron core heats up
  • Inefficient transfer of energy (also fire hazard)
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15
Q

Lamination as a solution to limitations of transformers

A

Iron core laminated by insulation sheets, introducing electrical discontinuity in the core
- Reduces eddy currents formed inside the core

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16
Q

Other solutions to limitations of transformers

A
  • Ferrite core can substitute iron core
    }Good mag flux transmitters, but poor electrical conductors
  • Water & oil as coolants
  • Fans to increase air circulation
  • Heat sinks to disperse heat elsewhere
17
Q

Electromagnetic Braking

A
  • Applies the EM induction principle
  • Metal wheels pass through magnetic field, eddy currents are produced in wheel
  • Eddy currents are induced in a specific way to counteract the motion of the wheel
18
Q

Advantages of EM Braking

A
  • Little to no noise
  • Smooth brake effect
19
Q

Disadvantages of EM Braking

A

EM Braking is incapable of holding the transport system after coming to rest. Mechanical braking still required

20
Q

DC Motors

A
  • Device which converts electrical energy into mechanical energy
  • DC current is fed through a coil in a magnetic field, which produces a rotation motion due to the motor effect
  • Current changes direction every 180
21
Q

DC Motor: Armature

A

The frame around which the coil of wire is around
Has an axis on which it can freely rotate

22
Q

DC Motor: Coil

A

One or more turns of wire wound around the armature

23
Q

DC Motor: Stator

A

Stationary/permanent/ electromagnet that provides the external, radial magnetic field around the coils
- Radial magnetic field ensures the sides of the coil are always travelling perpendicular to mag field

24
Q

DC Motor: SPLIT-ring commutator

A

Device with two metal semi-circular rings that reverses the direction of the current flowing in each coil every 180

24
Q

DC Motor: Brushes

A

Conducting contacts that connect the external circuit to the commutator

25
Q

Torque in DC Motor

A

t = BIAsin@

26
Q

Back EMF

A

The induced EMF produced in the coil of a motor due to its rotation in a magnetic field
EMFnet = V - EMFback

27
Q

Generators

A

A device which converts mechanical energy into electrical energy by applying the principle of electromagnetic induction

28
Q

AC Generator

A

SLIP Rings
- Two cylindrical metal conductors that rotate freely with the armature
- Constant electrical contact

29
Q

DC Generator

A

SPLIT Rings
- Flux-time graph identical to AC
- EMF-time graph always in one direction

Physics (6 decks)

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