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A2 Physics G495 > Chapter 15 > Flashcards

Chapter 15 Flashcards

1
Q

Define Faraday’s Law

A

Faraday’s law of electromagnetic induction states that the induced emf in a circuit is proportional to the rate of change of total magnetic flux through the circuit

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2
Q

What is the equation from Faraday’s law?

A

V=-d(phi)/dtwhere phi is the flux linkagealso emf, E=-Nd(phi)/dtwhere N is number of turns and phi is the flux density

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3
Q

Define Lenz’s law

A

The direction of the induced current in a circuit is always such as to oppose the change that causes it

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4
Q

Define magnetic flux

A

A term that refers to the lines of force. The lines of force are known as lines of flux, so we get the term flux density.

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5
Q

How do you calculate magnetic flux?

A

phi=BA where B is magnetic flux density and A is area swept out

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6
Q

How do you calculate flux linkage?

A

Phi=BAN=phiN where phi is magnetic flux and N is number of turns

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7
Q

How do you calculate the induced voltage when a rod of length L moves at 90deg. to magnetic field lines at speed v?

A

V=BLv

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8
Q

How are magnetic fields produced?

A

By current-carrying conductors or permanent magnets

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9
Q

What is a magnetic domain?

A

A region in a magnet with uniform magnetisation

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10
Q

How do you create a magnet?

A

Melt a ferrous metal slightly and tap it so all magnetic moments of the atoms align

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11
Q

How do you demagnatise a magnet?

A

Hit it really hard or heat and cool it quickly

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12
Q

How do you draw a wire, current going into the page?

A

Circle with a cross in it

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13
Q

What are the rules of drawing field lines?

A

Arrows go from north to southCan’t cross (vector quantity so just get resultant)Stronger fields when field lines are closer together

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14
Q

How do you tell the poles on a soleroid?

A

Clockwise current is north; anticlockwise current is south

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15
Q

What are the units of flux and flux density?

A

Flux: weberFlux density: Testler

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16
Q

How are current and flux related?

A

As current changes, so does flux as current-turns drive flux

17
Q

How are flux and induced emf related?

A

emf is the gradient of the flux graph

18
Q

What is the transformer equation?

A

Vs/Vp = Ns/Np = Ip/Is

19
Q

How are the voltage in the primary coil of a transformer and voltage in the secondary coil related?

A

Antiphase relationship

20
Q

How are current and voltage related?

A

Voltage is differential of current

21
Q

How does a transformer work?

A

Alternating current in the primary coilProduces a changing magnetic field in the secondary coilMutual induction:Alternating pd across primary coilProduces an alternating fluxIron core increases flux and guides it to the secondary coilSecondary coil experiences changing flux which induces an emf

22
Q

How are the currents related in the coils of a transformer?

A

Antiphase relationship

23
Q

What are the 2 equations for permeance?

A

Capital lamda, ^, permeance = flux/current turns = phi/NI^ = permeability*area/length =muA/L

24
Q

What is the left hand motor rule?

A

First finger field; second finger conventional current; thumb force

25
Q

What is a catapult force?

A

The force experienced by a wire when placed in a magnetic field. Initially, field lines are distorted, but wire moves to make them straighter and shorter

26
Q

How do you calculate a catapult force?

A

F=BIL where B is magnetic field strength, I is current and L is length of conductor

27
Q

What is the right hand generator rule?

A

First finger field; second finger conventional current, thumb motion

28
Q

What is back emf?

A

The emf due to the generator effect

29
Q

How is the power drawn split in a motor (equation)?

A

VI=E(back)I + I^2R where VI is power drawn, E(back)I is power to move current against back emf and I^2R is power lost to thermal energy

30
Q

What is the equation for calculating the emf at a specific rotation (angle from horizontal to perpendicular to coil)?

A

E=NBAwsin(wt)where N is no. turns, B is flux density, A is area, w is actually omega is is angular frequency and t is time.

31
Q

At what rotation is the maximum emf achieved?

A

When coil is parallel to field lines

32
Q

How is angular frequency calculated?

A

w=d(theta)/dt or w=2(pi)/T=2(pi)f where T is time period and f is frequency

33
Q

How do you calculate the maximum emf in a coil?

A

V=2(pi)f*peak flux linkage

A2 Physics G495 (4 decks)

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