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PHYSICS > DEFINITIONS OF UNIT 1 AND 2 > Flashcards

DEFINITIONS OF UNIT 1 AND 2 Flashcards

1
Q

ELECTRIC CURRENT

A

This is the rate of flow of electric charge

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2
Q

Efficiency of a system

A

% efficiency = 100* useful work out/ work put in

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3
Q

SCALAR

A

A QUANTITY THAT HAS MAGNITUDE ONLY

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4
Q

VECTOR

A

A QUANTITY THAT HAS MAGNITUDE AND DIRECTION

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5
Q

DENSITY

A

MASS / VOUME

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6
Q

MOMENT (OR TORQUE) OF A FORCE

A

THE MOMENT OF FORCE ABOUT A POINT IS DEFINED AS THE FORCE TIMES THE PERPENDICULAR DISTANCE FROM THE POINT TO THE LINE OF ACTION OF THE FORCE

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7
Q

THE PRINCIPLE OF MOMENTS

A

FOR A SYSTEM TO BE IN EQUILIBRIUM, THE SUM OF CLOCKWISE MOMENTS EQUALS TO THE SUM OF ANTICLOCKWISE MOMENTS OF THE SAME POINT

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8
Q

CENTRE OF GRAVITY

A

THE CENTRE OF GRAVITY IS THE SINGE POINT WITHIN BODY AT WHICH THE ENTIRE WIGHT OF THE BODY MAY BE CONSIDERED TO ACT

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9
Q

DISPLACEMENT

A

THE SHORTEST DISTANCE FROM A TO B, TOGETHER WITH ONE DIRECTION. UNIT: m

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10
Q

MEAN SPEED

A

TOTAL DISTANCE TRAVELED / TOTAL TIME TAKEN. UNIT: ms^-1

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11
Q

INSTANTANEOUS SPEED

A

RATE OF CHANGE OF DISTANCE

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12
Q

MEAN VELOCITY

A

TOTAL DISPLACEMENT/ TOTAL TIME TAKEN. UNIT: ms^-1

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13
Q

MEAN ACCELERATION

A

CHANGE IN VELOCITY/TIME TAKEN. UNIT: ms^-2

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14
Q

INSTANTANEOUS ACCELERATION

A

THE INSTANTANEOUS ACCELERATION OF A BODY IS ITS RATE O CHANGE OF VELOCITY. UNIT: ms^-2

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15
Q

TERMINAL VELOCITY

A

THE TERMINAL VELOCITY IS THE CONSTANT, MAXIMUM VELOCITY OF AN OBJECT WHEN THE RESISTIVE FORCES ON IT ARE EQUAL AND OPPOSITE TO THE ACCELERATING FORCE

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16
Q

FORCE

A

A FORCE ON A BODY IS A PUSH OR A PULL ACTING ON THE BODY FROM SOME EXTERNA BODY. UNIT: N

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17
Q

MOMENTUM

A

THE MOMENTUM OF AN OBJECT IS ITS MASS TIMES BY ITS VELOCITY (VECTOR). UNIT: Ns

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18
Q

THE PRINCIPLE OF CONSERVATION OF MOMENTUM

A

The vector sum of the momenta of bodies in a system stays constant even if forces act between the bodies, provided there is no external resultant force.

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19
Q

ELASTIC COLLISION

A

A collision in which there is no change in total kinetic

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20
Q

INELASTIC COLLISION

A

A collision in which kinetic energy Is lost.

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21
Q

WORK

A

Work done by a force is the product of the magnitude of the force and the distance moved in the direction of
the force. (W.D. = Fxcos 0)
Unit: J

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22
Q

PRINCIPLE OF CONSERVATION OF ENERGY

A

Energy cannot be created or destroyed, only transferred from one form to another. Energy is a scalar.

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23
Q

POTENTIAL ENERGY

A

This is energy possessed by an object by virtue of its
position. E, = mgh Unit: J

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24
Q

KINETIC ENERGY

A

This is energy possessed by an object by virtue of its motion. Ex= ½mv Unit: J

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25
Q

ELASTIC POTENTIAL ENERGY

A

This is the energy possessed by an object when it has been deformed due to forces acting on it.
elastic = ½ Fx Unit: J

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26
Q

ENERGY

A

The energy of a body or system is the amount of work it can do.
Unit: J

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27
Q

POWER

A

This is the work done per second, or energy transferred per second. Unit: W [= Js*]

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28
Q

SPRING CONSTANT

A

The spring constant is the force per unit extension.
Unit: Nm’’

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29
Q

STRESS

A

Stress is the force per unit cross-sectional area when equal opposing forces act on a body.
Unit Pa or N m

30
Q

STRAIN

A

Strain is defined as the extension per unit length due to an applied stress. Unit: none

31
Q

YOUNG MODULUS

A

YOUNG MODULUS= TENSILE STRESS/ TENSILE STRAIN
Unit: Pa or N m2

32
Q

CRYSTAL

A

Solid in which atoms are arranged in a regular array. There is a long range order within crystal structures.

33
Q

CRYSTALLINE SOLID

A

Solid consisting of a crystal, or of many crystals, usually arranged randomly. The latter is strictly a polycrystalline solid. Metals are polycrystalline.

34
Q

AMORPHOUS SOLID

A

A truly amorphous solid would have atoms arranged quite randomly. Examples are glass or brick

35
Q

POLYMERIC SOLID

A

A solid which is made up of chain-like molecules.

36
Q

DUCTILE MATERIAL

A

A material which can be drawn out into a wire. This implies that plastic strain occurs under enough stress.

37
Q

ELASTIC STRAIN

A

This is strain that disappears when the stress is removed, that is the specimen returns to its original size and shape.

38
Q

PLASTIC STRAIN

A

This is strain that decreases only slightly when the stress is removed. In a metal it arises from the movement of dislocations within the crystal structure.

39
Q

ELASTIC LIMIT

A

This is the point at which deformation ceases to be elastic. For a specimen it is usually measured by the maximum force, and for a material, by the maximum stress, before the strain ceases to be elastic.

40
Q

DUCTILE FRACTURE

A

The characteristic fracture process in a ductile material. The fracture of a rod or wire is preceded by local thinning which increases the stress.

41
Q

BRITTLE MATERIAL

A

Material with no region of plastic flow, which, under tension, fails by brittle fracture:

42
Q

BRITTLE FRACTURE

A

This is the fracture under tension of brittle materials by means of crack propagation.

43
Q

ELASTIC HYSTERESIS

A

When a material such as rubber is put under stress and the stress is then relaxed, the stress-strain graphs for increasing and decreasing stress do not coincide, but form a loop. This is hysteresis.

44
Q

BLACK BODY

A

A black body is a body (or surface) which absorbs all the electromagnetic radiation that falls upon it.

45
Q

LUMINOSITY OF A STAR

A

The luminosity of a star is the total energy it emits per unit time in the form of electromagnetic radiation.
UNIT: W

46
Q

POTENTIAL DIFFERENCE

A

The pd between two points is the energy converted from electrical potential energy to some other form per coulomb of charge flowing from one point to the other. Unit: V [= J C*]

47
Q

ELECTRICAL RESISTANCE

A

The resistance of a conductor is the pd (V) placed across it divided by the resulting current (1) through it.
Unit: VA^-1

48
Q

SUPERCONDUCTING TRANSITION TEMPERATURE

A

The temperature at which a material, when cooled, loses all its electrical resistance, and becomes super-conducting. Some materials (e.g. copper) never become superconducting however low the temperature becomes.

49
Q

Emf

A

The emf of a source is the energy converted from some other form (e.g. chemical) to electrical potential energy per coulomb of charge flowing through the source. Unit: V

50
Q

PROGRESSIVE WAVE

A

A pattern of disturbances travelling through a medium and carrying energy with it, involving the particles of the medium oscillating about their equilibrium positions.

51
Q

TRANSVERSE WAVE

A

A transverse wave is one where the particle oscillations are at right angles to the direction of travel (or propagation) of the wave.

52
Q

LONGITUDINAL WAVE

A

A longitudinal wave is one where the particle oscillations are in line with (parallel to) the direction of travel (or propagation) of the wave.

53
Q

POLARISED WAVE

A

A polarised wave is a transverse wave in which particle oscillations occur in only one of the directions at right angles to the direction of wave propagation.

54
Q

IN PHASE

A

Waves arriving at a point are said to be in phase if they have the same frequency and are at the same point in their cycles at the same time.

55
Q

WAELENGTH OF A PROGRESSIVE WAVE

A

The wavelength of a progressive wave is the minimum distance between two points on the wave oscillating in phase.

56
Q

FREQUENCY OF A WAVE

A

The frequency of a wave is the number of cycles of a wave that pass a given point in one second.

57
Q

SPEED OF A WAVE

A

The speed of a wave is the distance that the wave profile moves per unit time.

58
Q

DIFFRACTION

A

Diffraction is the spreading out of waves when they meet obstacles, such as the edges of a slit. Some of the wave’s energy travels into the geometrical shadows of the obstacles.

59
Q

PHASE DIFFERENCE

A

Phase difference is the difference in position of 2 points within a cycle of oscillation. It is given as a fraction of the cycle or as an angle, where one whole cycle is 2m or 360°], together with a statement of which point is ahead in the cycle.

60
Q

COHERENCE

A

Waves or wave sources, which have a constant phase difference between them (and therefore must have the same frequency) are said to be coherent

61
Q

STATIONARY WAVE

A

A stationary wave is a pattern of disturbances in a medium, in which energy is not propagated. The amplitude of particle oscillations is zero at equally-spaced nodes, rising to maxima at antinodes, midway between the nodes.

62
Q

CRICTAL ANGLE

A

When light approaches the boundary between two media from the ‘slower’ medium, the critical angle is the largest angle of incidence for which refraction can occur. The refracted wave is then travelling at 90° to the normal.

63
Q

PHOTOELECTRIC EFFECT

A

When light or ultraviolet radiation of short enough wavelength falls on a surface, electrons are emitted from the surface.

64
Q

WORK FUNCTION

A

The work function of a surface is the minimum energy needed to remove an electron from the surface. Unit: J or eV.

65
Q

ELECTRON VOLT

A

This is the energy transferred when an electron moves between two points with a potential difference of 1 V between them. 1 eV = 1.60 × 10-19 J
So for an electron being accelerated it is the kinetic energy acquired when accelerated through a pd of 1

66
Q

IONISATION

A

The removal of one or more electrons from an atom.

67
Q

IONISATION ENERGY

A

The ionization energy of an atom is the minimum energy needed to remove an electron from the atom in its ground state. Unit: J

68
Q

STIMULATED EMISSION

A

This is the emission of a photon from an excited atom, triggered by a passing photon of energy equal to the energy gap between the excited state and a state of lower energy in the atom. The emitted photon has the same frequency, phase, direction of travel and polarisation direction as the passing photon.

69
Q

POPULATION INVERSION

A

A POPULATUON INVERSION IS A SITUATION IN WHICH A HIGHER ENERGY STATE IN AN ATOMIC SYSTEM IS MOREE HEAVILY POPULATED THAN A OWER ENERGY STATE OF THE SAME SYSTEM

70
Q

PUMPING

A

PUMPING IS FEEDFING ENERGY INTO THE AMPLIFYING MEDIUM OF A LASER TO PRODUCE A POPULATION INVERSION

PHYSICS (11 decks)

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