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Module 2 Flashcards

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1
Q

Definition of density?

A

mass per unit volume

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2
Q

Units of density?

A

kg m^-3

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3
Q

Hookes Law?

A

Extension is proportional to the force applied, up to the limit of proportionality

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4
Q

What are the features of graph force against extension confirming Hooke’s Law?

A

There is a straight line through the origin of the graph.

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5
Q

Units of spring constant?

A

Nm^-1

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6
Q

Rules of springs in series

A
  • Both springs experience the dame Force (F)

- The total extension (of both springs together) is the sum of the extension of each spring individually.

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7
Q

Rules of (identical) springs in parallel

A
  • The Force (F) applied to the spring combination is shared across each of the springs individually (if there are two identical springs, each spring experiences a force of 1/2F).
  • All the springs have the same extension (and equals the extension for the spring combination.
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8
Q

Definition of Elastic Limit?

A

The maximum amount a material can be stretched by a force and still return to its original length when the force is removed.

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9
Q

Definition of Limit of Proportionality

A

Point beyond which force is no longer proportional to extension

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10
Q

Definition of elastic behaviour?

A

Material will return to its original length (when force removed) with no permanent extension.

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11
Q

Definition of plastic behaviour?

A

Material will be permanently extended (when force is removed)

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12
Q

What does area under a force/extension graph show you?

A
  • Area under a graph of force against extension is work done on spring and hence the energy stored, as it is loaded.
    OR
  • Area under a graph of force against extension is the work done by the spring, and hence energy released, as it is unloaded.
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13
Q

What does the area between the loading and unloading curves of an elastic band?

A

Internal energy retained, e.g. as heat, within the elastic band.

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14
Q

Explain the derivation of energy stored = ½ FL?

A
  • Energy stored in a stretched spring = work done stretching spring
  • Work done = Force x distance (moved in the direction of the force)
  • As spring is stretched, the force gets bigger (and so isn’t constant)
  • Force is proportional to extension, so, the average force = F/2 which = 1/2F
  • The work done = average force x distance moved
  • energy stored = work done = ½ FL
  • This is the area under the graph of Force against Extension (1/2base x height)
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15
Q

Explain the Derivation of energy stored = ½ FL from a graph of force against extesion

A
  • W=Fs, so the area beneath the line from origin to L represents the work done to compress/extended spring.
  • Work done (on spring) equals the energy it stores.
  • Area under graph = area of triangle = 1/2base x height, therefore energy stored = ½ F x L.
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16
Q

What is the definition of tensile stress?

A

Tensile (stretching) force divided by its cross-sectional area

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17
Q

What are the units of stress?

A

Pa or Nm^-2

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18
Q

What is the definition of tensile strain?

A

It’s the extension of material divided by its original length

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19
Q

What are the units of strain?

A

None

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20
Q

What is the definition of breaking stress?

A

Stress needed to break a solid material.

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21
Q

What is the description of stiffness?

A

Requires a large force (or stress) for a small deformation (or extension)

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22
Q

What is the description of fracture?

A
  • Non-brittle fracture: Material necks which reduces the cross-sectional area so increases stress at that point until the wire breaks.
  • Brittle fracture
    No plastic deformation, usually snaps suddenly without any noticeable yield.
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23
Q

What is the description of brittle?

A

A material that fractures without any plastic deformation.

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24
Q

What is the description of ductile?

A

When a material can be draw into a wire (exhibits a lot of plastic deformation)

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25
Q

Description of strength (or weakness)?

A

Material with a higher (or lower) breaking stress.

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26
Q

What is the definition of the Young Modulus?

A

It’s the ratio of tensile stress to tensile strain.

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27
Q

What is the unit of the Young Modulus?

A

Pa or Nm^-2

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28
Q

What is the use of stress/strain curves to find young modulus?

A

From a graph of stress against strain, Young Modulus is the gradient of the linear section of the graph (the region where the stress and strain are directly proportional).

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29
Q

What does the area under the graph of stress against strain show?

A

The energy stored per unit volume.

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30
Q

Explain one simple method of measuring Young Modulus

A
  • Measurements to make
    + Original length of wire,L, with a ruler
    + Diameter of wire with a micrometer
    + Mass attached to end of wire
    + Length of stretched wire with a ruler
  • Reducing Uncertainty in each measurement
    + Repeat measurements of length
    + Repeat measurements of diameter of wire at different points
    + Check for zero error on electronic scales
    + Check for zero error on micrometer
  • How measurements are used to determine Young Modulus
    + F=weight=mg
    + Extension L = stretched length - original length
    + Cross sectional area of wire A = d2 / 4
    + Stress = F/A; Strain = L/L
    + Plot a graph of stress (y-axis) against strain (x-axis)
    + Young Modulus is gradient of linear section of the graph
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31
Q

What is the difference between a scalar and a vector?

A

Vector has magnitude and direction, whereas scalar only has magnitude.

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32
Q

What are some examples of scalar quantities?

A
  • Speed
  • Mass
  • Time
  • Energy
  • Power
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33
Q

What are some examples of vector quantities?

A
  • Displacement
  • Velocity
  • Acceleration
  • Force
  • Weight
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34
Q

How do you add perpendicular vectors by calculation?

A
  • You draw the vectors a a right angled triangle.
  • Then use the pythagoras theorem to find the magnitude of resultant vector
  • Use trigonometry to calculate the angle of resultant vector.
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35
Q

How to add vectors by scale drawing?

A
  • Write down scale eg 1cm=2N
  • Draw the vectors to correct length and angle to each other “tip to tail”
  • The add the resultant vector line
  • Measure the length and angle of resultant vector
  • Convert length into appropriate quantity to find magnitude of resultant vector.
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36
Q

`What are the conditions for equilibrium of two or three coplanar forces acting at a point?

A
  • Total resultant equals zero
    OR
  • If the vectors representing the forces are added together they will form a closed triangle.
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37
Q

What are the two conditions for a body to remain in equilibrium?

A
  1. Resultant force acting on body is zero

2. Resultant moment about any point is zero.

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38
Q

What is the definition of a moment?

A

Force multiplied by the perpendicular distance between the line of action of the force and the pivot.

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39
Q

What are the units of a moment?

A

Nm

40
Q

What is the principle of a moment?

A

In equilibrium, the sum of the clockwise moments about a point equals the sum of the anticlockwise moments.

41
Q

What is the definition of moment of a couple?

A

(one) force multiplies by the perpendicular distance between the lines of actions of the two forces.

42
Q

What is the definition of centre of mass?

A
  • The point in a body through which weight appears to act
    OR
  • The point in a body where the resultant moment is zero.
43
Q

What is a stable equilibrium?

A

When a body is displaced then released, it will return to its equilibrium position.

44
Q

What is an unstable equilibrium?

A

When a body is displaced then released it will not return to its equilibrium position.

45
Q

What is displacement defined as?

A

The distance in a given direction.

46
Q

What is velocity defined as?

A
  • The rate of change of displacement
    OR
  • The change in displacement divided by the time taken
47
Q

What is acceleration defined as?

A
  • The rate of change of velocity
    OR
  • The change in velocity divided by time taken
48
Q

What does the gradient of displacement and velocity time graphs mean?

A
  • Gradient of a displacement time graph = velocity

- Gradient of a velocity time graph = acceleration

49
Q

What does the area under velocity and acceleration time graphs mean?

A
  • Area under a velocity time graph = displacement

- Area under an acceleration time graph = velocity

50
Q

What is the average velocity?

A

It is the total displacement divided by total time

51
Q

What is the instantaneous velocity at a point?

A
  • It is the rate of change of displacement at that point

- Gradient at a point on a displacement time graph.

52
Q

What are the conditions for an object falling at terminal velocity?

A
  • Resultant force on object is zero
  • Acceleration is zero
  • Object travels at a constant velocity
53
Q

What are the factors affecting drag force on an object?

A
  • The shape of the object
  • It’s speed
  • The viscosity of the fluid/gas
54
Q

Explain why an object reaches terminal velocity falling through air?

A
  • Initially only force acting is weight, so object accelerates at g.
  • Drag force increases with increasing speed
  • Therefore resultant force decreases
  • Eventually drag force = weight, forces are balanced
  • So resultant force is zero
  • As F=ma, acceleration is zero so object falls at constant speed.
55
Q

What is the horizontal and vertical motion of a projectile in absence of resistive forces?

A
  • Horizontal motion: no force horizontally, no acceleration so constant velocity.
  • Vertical motion: constant force due to weight, constant acceleration (equal to g)
56
Q

What are Newton’s 3 laws of motion?

A
  • 1st law: An object will continue at rest or uniform velocity unless acted on by a resultant force.
  • 2nd law: The acceleration of an object id proportional to resultant force acting on it, i.e. F=ma (providing mass is constant)
  • 3rd law: If object A exerts a force on a second object B, then object B will exert an equal and opposite force on object A.
57
Q

What is the principle of conservation of energy?

A

Energy is neither created or destroyed, only converted from one form to another.

58
Q

What are the energy conversions of an object falling in presence of resistive forces?

A

loss in g.p.e =gain in k.e. + work done against resistance work done typically appears as heat.

59
Q

What is the definition of work done?

A

It means the force multiplied by distance moved in the direction of the force.

60
Q

What is the unit of work done?

A

J

61
Q

What is the definition of power?

A
  • The rate at which energy is transferred
    OR
  • Energy transferred (work done) divided by time taken
62
Q

What are the units of power?

A

W (watts) or Js^-1

63
Q

What is a longitudinal wave?

A

When a particle vibration is parallel to the direction of the wave propagation.

64
Q

What are some example of a longitudinal wave?

A

Sound waves, seismic p-waves.

65
Q

What is a transverse wave?

A

When a particle vibration is perpendicular to the direction of wave propagation.

66
Q

What is particle displacement?

A

The distance of a particle from its equilibrium position in given direction

67
Q

What is the definition of amplitude?

A

It is the maximum displacement of a particle (wave) from its equilibrium (or rest) position

68
Q

What is the definition of frequency?

A

It is the number of oscillations (of a particle) per second

69
Q

What is the definition of a time period?

A

The time for one complete oscillation

70
Q

What is the definition of a wave length?

A

It is the shortest distance between two points in phase.

71
Q

What is the definition of diffraction?

A

It is the the spreading out of a wave (when it passes through a gap or past the edge of an object)

72
Q

What is the definition of refraction?

A

It is when the wave bends/changes direction when its speed changes

73
Q

What is the definition of polarisation?

A

(transverse) wave oscillation is in one plane

74
Q

Explain the application of polarisation in sunglasses?

A
  • Light reflected from surfaces is (weakly) polarised in one plane (horizontal)
  • Polaroid in sunglasses can be orientated to remove this reflected light
  • Reducing glare
75
Q

Explain the application of polarisation in tv transmitters and aerials?

A
  • Signals from tv transmitter (radio waves) are polarised
  • Aerials need to be orientated (rotated) so they are in the same plane as the transmitted signal
  • For maximum signal strength
76
Q

What is superposition?

A

Where two or more waves meet, the resultant displacement equals the vector sum of the individual displacements

77
Q

What are the conditions for formation of stationary waves?

A
  • Two waves travelling past each other in opposite directions
  • With the same wavelength (frequency)
  • Similar amplitude
78
Q

What are nodes and anti-nodes?

A

Nodes- points of no oscillation/ zero amplitude

Anti-nodes - points of maximum amplitude.

79
Q

What are coherent sources?

A

Waves (from two sources) that have:

  • a constant phase difference
  • same wavelength (or frequency)
80
Q

What does monochromatic?

A

Single wavelength

81
Q

What are the rules of safety with a laser?

A
  • Avoid looking along the beam of a laser
  • Wear laser safety goggles
  • Avoid reflections
  • Put up a warning sign that a laser is in use.
82
Q

What are the properties of laser light?

A
  • Monochromatic - only a single wavelength
  • Coherent - waves have a constant phase difference
  • Collimated - produces an approximately parallel beam.
83
Q

Explain the formation of fringes with Young’s slits?

A
  • Interference fringes formed
  • Where light from two slits overlaps
  • The light from the two slit is coherent
  • Bright fringes formed where constructive interference
  • Because light from the two slits is in phase (path difference equals a whole number of wavelengths)
  • Dark fringed formed where destructive interference
  • Because light from the two slits in anti-phase (path difference equals a whole number +0.5 wavelengths)
84
Q

Explain the appearance of white light through Young’s slits?

A
  • Central fringe would be white
  • Side fringes are (continuous) spectra
  • Bright fringe would be blue on the side nearest the central fringe
  • Bright fringes merge further away from the centre
85
Q

Explain the appearance of diffraction pattern from a single slit?

A
  • Central bright fringe has twice width of other bright fringes
  • The other bright fringes have a much lower intensity
  • and are equally spaced
86
Q

What are the applications of gratings to spectral analysis of light from stars?

A
  • Dark lines in spectrum from a star (absorption spectrum)

- Reveal the composition of (elements present in) the star’s atmosphere

87
Q

How does light change moving from air to glass?

A
  • speed - decreases
  • wavelength - decreases
  • frequency - remains constant
88
Q

What are the conditions for total intolerant reflection?

A
  • Angle of incidence is greater than the critical angle
  • The refractive index of the material light is going from is greater than the refractive index of the material the light is going to.
89
Q

What is total internal reflection?

A

Where all the light is reflected back into the material

90
Q

What is the critical angle?

A

Angle of incidence which produces an angle of refraction of 90 degrees.

91
Q

What is the structure of an optical fibre?

A
  • Central core, surrounded by cladding.

- Refractive index of core must be greater than the refractive index of cladding (to ensure total internal reflection)

92
Q

What is the purpose of cladding?

A
  • prevents crossover of signal/data to other fibres
  • prevents scratching of the core
  • reduces pulse broadening/dispersion
93
Q

What are the uses of optical fibres?

A
  • Communication - improve transmission of data/high speed internet
  • Endoscopes - improved medical diagnosis
94
Q

How do pulses of light change travelling down optical fibres?

A
  • reduced amplitude due to absorption/energy loss and scattering within fibre
  • pulse broadening due to multipath dispersion from rays taking different paths and different times to travel down same fibre
95
Q

How is multipath dispersion reduced?

A

Core of fibre is made very narrow/thin

Physics As (2 decks)

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