eLFH - Magnetism and Current Flashcards

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1
Q

Link between magnetism and electricity

A

Conductor carrying electrical charge or current creates a magnetic field - i.e. magnetic field can be created using electrical power

A wire moved through a magnetic field induces electric current in the wire proportional to its speed of movement - e.g. a dynamo

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2
Q

Magnetic flux

A

The lines drawn that represent the effect of a magnetic field around magnet or electrical conductor

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3
Q

Flux density

A

If magnetic flux lines are close together, flux density is high

Current induced in an electrical conductor moving through a magnetic flied with higher flux density is greater than that of low flux density

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4
Q

Flux density of Earth’s magnetic flied

A

Low flux density

But overall high total magnetic strength

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5
Q

Total flux definition

A

Flux density summed over an area

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6
Q

Units of flux density

A

Tesla

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7
Q

Force equation for force exerted by charge moving perpendicular to magnetic field

A

F = Q x U x B

F is force (Newtons)
Q is electric charge (Coulombs)
U is velocity perpendicular to magnetic field (m/sec)
B is magnetic flux density (tesla)

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8
Q

Magnetisation curve for ferromagnetic materials

A

As increasing magnetic field strength applied to ferromagnetic material, it passes through different regions of magnetic flux

Reversible to irreversible magnetism

Once the domains are irreversibly aligned (saturated) the metal is a magnet

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9
Q

Magnetic hysteresis definition

A

If applied magnetic flied to a material is removed, the magnetic flux density does not always return to zero

Material remains weakly magnetised

This is Hysteresis

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10
Q

Direction of magnetic field created by electrical current

A

Magnetic flied runs clockwise around the wire when looking in the direction if the current flow

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11
Q

Effect for coiling a wire on magnetic field and why

A

More intense magnetic field with coiled wire
Flux density increases as many times as there are coils

Neighbouring coils induce neighbouring reinforcing magnetic flux

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12
Q

Voltage equation for a coiled wire

A

Voltage induced by coil = number of turns in coil x rate of change of magnetic flux

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13
Q

Types of core that can be used in wire coil

A

Air

Iron

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14
Q

Why does iron core in coiled wire have greater flux density than air core

A

High magnetic permeability of iron

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15
Q

Equation for flux density

A

B is flux density
Mu is magnetic permeability
H is strength of magnetic field applied to material

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16
Q

Mutual inductance in a transformer

A

2 separate circuits coiled around same iron core

Electrical current in one circuit creates magnetic field which generates current in second coiled wire without it being connected to any mains power

17
Q

Use of isolating transformers

A

Allows floating circuits to be made which are not earthed - only circuit connected to mains is earthed but circuit connected to patient is not

Therefore from floating circuit, cannot be electrocuted

Used to isolate individual instruments

18
Q

Effect of adjusting number of coils on each side of a transformer

A

Can step up or step down voltage between input and output depending on number of coils on primary and secondary winding

V1 / V2 = N1 / N2
I1 x N1 = I2 x N2

19
Q

Wire coils in transformer material and why

A

Copper

Reduce losses

20
Q

Material used for core of transformers and why

A

Steel

high magnetic permeability to reduce hysteresis losses

21
Q

Why is transformer laminated

A

Reduce eddy current loss

22
Q

Eddy current definition

A

Opposing flows of electrical current that can develop due to variations in magnetic field or relative movement of the conductor

These flows induce own magnetic field that result in resistive losses

23
Q

Function of Earth’s magnetic field

A

Protects against cosmic and solar radiation