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BMAT Physics > General > Flashcards

General Flashcards

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1
Q

How can insulators be charged by friction?

A

They are rubbed against each other, one becomes positive, the other negative

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2
Q

How does charging by induction work?

A

An uncharged object placed near a charged object becomes charged as electrons are transferred.

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3
Q

What is charging?

A

The gain or loss of electrons

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4
Q

In which direction do magnetic field lines go?

A

From north to south to form closed loops

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5
Q

What is the difference between hard and soft materials in terms of magnetism?

A

Soft materials gain and lose magnetisation very quickly

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6
Q

What can cause a magnetic material to lose its magnetism?

A

Time
Hitting it
Heat

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7
Q

What is the magnetic effect of a current?

A

Create magnetic fields in a surrounding space, so cause a compass to deflect from north. Degree of deflection depends on size of current. Reversing the current changes the deflection.

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8
Q

Explain the right hand rule

A

A fist with the thumb point up
Thumb = direction current
Fingers = direction of field lines

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9
Q

What is the magnetic field pattern of a coil and why?

A

Magnetic field created by each part of the coil combine to a create a strong field through the coil.

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10
Q

Which end of a coil is clockwise or anticlockwise?

A 
Clockwise = south pole
Anticlockwise = north pole
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11
Q

Why is iron used as a core in magnets?

A

It is ferromagnetic
When an external magnetic field from a current-carrying wire or coil passes through a ferromagnetic material, the atomic magnets can line up with the external field to create a much stronger resultant field.

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12
Q

How can you increase the magnetic strength of a solenoid?

A

Soft iron core
More turns per unit length
Increasing current

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13
Q

What happens to a wire carrying a current in a magnetic field?

A

It experiences a force (motor effect)

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14
Q

Explain the left hand rule

A

Forefinger = direction of magnetic field (N to S)
Middle finger = direction of current (+ to -)
Thumb = direction of motor effect force

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15
Q

Unit for strength of magnetic field

A

Tesla

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16
Q

What is F = BIL

A

F=BIL

F is the motor effect force in newtons (N).

B is the magnetic field strength in tesla (T).

I is the current in the wire in amps (A).

L is the length of wire at 90° to the magnetic field in metres (m).

The direction of the force is given by the left-hand rule.

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17
Q

What is a split ring commutator?

A

Reverses the direction of current every half turn, allowing the motor coil to rotate continuously in one direction

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18
Q

What happens when a wire cuts magnetic field lines?

A

A voltage is induced

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19
Q

What does electromagnetic induction result in?

A

Always a voltage, a current if there is a closed circuit

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20
Q

What factors affect the magnitude of an induced voltage?

A

The rate at which a wire cuts magnetic field lines

or

The rate at which the magnetic field through a conductor (eg a coil) changes

And the strength of the magnet

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21
Q

In which direction is an induced voltage?

A

Against the direction of the change that caused it

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22
Q

How can you increase the output of an AC generator?

A

Rotate coil more rapidly
Stronger magnetic field
Coil has greater area
More turns on coil

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23
Q

What does a step up transformer do?

A

Increases the voltage

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24
Q

A transformer has has more turns on the primary than secondary coil. What will the output voltage be?

A

Lower

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25
Q

What is the equation for the coils and pds in a transformer?

A

Vp/Vs = np/ns

26
Q

What is the relationship between voltage and current in a transformer?

A

VpIp = VsIs

27
Q

Why are high voltages used in transmission lines?

A

Keeps current low, so reduced loss due to heating of the cables

28
Q

What is the equation for power wasted in a transmission line?

A

P=I^2 * R

29
Q

Do transformers work with AC or DC?

A

AC

30
Q

Why do we need to step down voltage?

A

Harder to insulate

31
Q

What is the equation for Hooke’s law?

A

F=kx

Force applied = constant * change in length

32
Q

Equation for energy stored in a stretched spring?

A

E=1/2 k x^2

33
Q

What factors affect spring constant?

A

Greater cross sectional area = greater spring constant

Longer wire = smaller spring constant

34
Q

State newtons first law

A

A body will remain at rest or in a state of uniform motion in a straight line unless acted on by a resultant external force

35
Q

State newtons second law

A

force = mass × acceleration

36
Q

State newtons third law

A

If body A exerts a force on body B then body B exerts an equal and opposite force of the same type on body A

37
Q

What is the equation for momentum?

A

momentum = mass * velocity

38
Q

How does force relate to rate of change of momentum?

A

force = rate of change of momentum

39
Q

What is the equation for work done?

A

Work = force * distance moved

40
Q

What is the equation for GPE?

A

gpe = mgh

41
Q

What is the equation for kinetic energy?

A

1/2 m * v^2

42
Q

What is the equation for power?

A

energy transfer/time

43
Q

Why does temperature plateau?

A

For example at the melting point

All energy goes into breaking bonds

44
Q

In what three ways can heat be transferred?

A

Conduction
Convection
Radiation

45
Q

What is conduction?

A

particles pass on kinetic energy to their neighbours without actually moving

46
Q

What is convection?

A

This occurs when higher energy particles move to cooler regions, heating them up

47
Q

What is radiation?

A

heat transfer by the emission of infra-red electromagnetic waves

48
Q

How do you work out specific heat capacity?

A

shc = thermal energy / (mass * temperature change)

49
Q

What is the relationship between pressure volume and constant temperature?

A

PV = constant

50
Q

What is specific latent heat

A

specific latent heat of a substance is the amount of energy needed to change the state of 1 kg of the substance without changing its temperature

51
Q

What is specific heat capacity?

A

Specific heat capacity is defined as the amount of heat required to raise the temperature of 1 kilogram of a substance by 1

52
Q

What is the equation for specific latent heat?

A

E=mL

Energy transferred = mass * slh

53
Q

How do you work out hydrostatic pressure?

A

Hydrostatic pressure = hpg (height * density * gravity)

54
Q

What is a transverse wave?

A

the vibration direction is perpendicular to the wave direction

55
Q

What is a longitudinal wave?

A

the vibration direction is parallel to the wave direction

56
Q

How do you work out frequency?

A

1/period

57
Q

How do you work out wave speed?

A

distance/time

frequency * wavelength

58
Q

What happens when a light ray slows down?

A

Refracts towards the normal

59
Q

What happens when a light ray speeds up?

A

Refracts away from the normal

60
Q

What is the doppler effect?

A

When there is relative motion between a source of waves and an observer, the wavelength and frequency of the waves detected by the observer is different from the wavelength and frequency of the waves received when there is no relative motion

61
Q

Is the em spectrum longitudinal or transverse?

A

Transverse

BMAT Physics (1 decks)

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