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PHYSICS > Book Three > Flashcards

Book Three Flashcards

work, energy, power - deformation of solids - waves - superposition

1
Q

what is work? + formula, SI unit

A

work is done when a force moves its point of application in the direction of the force
work = force x displacement
Joule (equivalent to Nm)

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2
Q

what is the joule?

A

the work done when a force of 1 newton moves its point of application by one metre in its direction

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3
Q

what is efficiency? + formula, SI unit

A

the ratio of the useful work done by a machine or in a process to the total energy or heat taken in.
efficiency = useful energy output / useful energy input

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4
Q

what is energy? + formula, SI unit

A

the ability to do work
power x time
Joule

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5
Q

what is energy conversion?

A

change of energy from one form to another

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6
Q

principle of conservation of energy

A

it states that energy can neither be created nor destroyed , but can be transformed from one form to another

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7
Q

forms of energy

A

potential - energy due to position or condition
kinetic - energy due to motion
elastic/strain - energy due to stretching of a body
electrical - energy due to moving electric charge
sound - energy due to particles in a wave
wind - energy due to wind
light - energy due to electromagnetic waves
solar - energy from the sun
chemical - energy released during chemical reaction
nuclear - energy associated with particles in atomic nucleus
thermal - also known as heat energy
*chemical & electrical are high grade, everything else is low grade

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8
Q

what is potential energy? + formula, SI unit

A

this is energy due to position or condition
Ep = mgΔh
Joule

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9
Q

forms of potential energy

A
  1. gravitational potential energy (gpe) - energy due to position in the earths gravitational field
  2. elastic potential energy - energy stored in a body that has had its shape changed elastically
  3. electrical potential energy - energy due to attraction and repulsion of charges
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10
Q

what is kinetic energy? + formula, SI unit

A

this is energy due to motion
Ek = 1/2mv^2
Joule

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11
Q

what is power? + formula, SI unit

A

this is the rate or energy transfer/ doing work
power = energy / time or work done / time
Watt

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12
Q

deformation of a solid + types

A

this is change in the shape of a solid when a force is applied on it
- tensile (when it stretches)
- compressive (when its squashed)

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13
Q

what does extension of a solid depend on?

A
  1. nature of the material
  2. size of the stretching force
  3. area of cross-section of the sample
  4. original length of the sample
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14
Q

what is stress? + formula, SI unit

A

this is force acting normally per unit area of cross-section of a material
stress = force / area
Pa

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15
Q

differences in pressure and stress

A

p. is the external force applied at a point
s. is the resistive force developed at a point
p. always acts normal to the surface
s. acts normal or parallel to the surface
p. at a point, is the same in all directions
s. at a point, isn’t the same in all directions
p. causes stress
s. doesn’t cause pressure
p. has measuring devices
s. has no measuring device
p. is a scalar quantity
s. is a tensor quantity

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16
Q

what is strain? + formula, SI unit

A

extension per unit length of a material
strain = extension / original length
its a ratio so it has no unit

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17
Q

what is hooke’s law? + formula

A

it states that extension of an elastic material is directly proportional to the stretching force applied to it given the elastic limit is not exceeded
F = kx
where k is spring constant

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18
Q

what is spring constant? + SI unit

A

is defined as force per unit extension of a material
Nm^-1

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19
Q

what is young modulus? + formula, SI unit

A

is stress divided by strain on a material
E = σ / ε
Pa

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20
Q

state the mechanical properties of materials

A

strength - a measure of applied force a material can withstand before breaking

stiffness - a measure of the opposition a material sets up to being distorted by having its shape/size changed

ductility - the ability of a material to be hammered, bent, pressed, rolled or drawn into shaped

toughness - on that is not brittle
*steel has all four properties

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21
Q

what is strain energy? + formula

A

energy stored up in a body due to its change of shape
1/2kx^2

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22
Q

what is a wave?

A

repeated vibration which transfers energy from one point to another without transferring matter

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23
Q

what is displacement, x ? + SI unit

A

the distance of a point on the wave from its rest position
metre

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24
Q

what is amplitude, a ? +SI unit

A

maximum displacement of a particle from its rest position
metre

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25
Q

what is wavelength, λ ? + SI unit

A

the distance between 2 adjacent crests or troughs
metre

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26
Q

what is frequency, f ? + SI unit

A

number of complete waves passing any point per second
unit - s^-1
SI unit - Hertz, Hz
*f = 1/T

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27
Q

what is wave speed, v ? + SI unit

A

the speed with which energy is transmitted by the wave
ms^-1

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28
Q

what is a wave front?

A

a line joining points at the same position along a wave

29
Q

what is in phase?

A

when a crest is aligned with a crest

30
Q

what is out of phase?

A

when a crest is aligned with a trough for example

31
Q

what is phase difference, Φ ? + formula, SI unit

A

the amount by which one oscillation leads or lags behind another
Φ = x / λ x 360° or Φ = t / T x 360°
Φ = x / λ x 2π or Φ = t / T x 2π
degrees, ° or radians, rads

32
Q

wave equation

A

speed = distance / time
v = f

33
Q

what is intensity? + formula, SI unit

A

the amount of energy passing through unit area per unit time
I = P / A
watts per square metre , Wm^-2

34
Q

what is the relationship between intensity, amplitude and frequency?

A
  • intensity is directly proportional to the square of the amplitude of a wave
  • intensity is directly proportional to the square of the frequency of a wave
  • for a wave of amplitude a and frequency f, I ∝ a^2f^2
35
Q

what is the intensity of spherical waves?

A

I = P / 4πr^2
where
- 4πr^2 is the surface area of the sphere
- P power of the source
I ∝ 1 / r^2
where
- r is the distance from the source
so
- I decreases with increase in r

36
Q

what are transverse waves? +example

A

waves in which the particles vibrate perpendicular to the direction of energy transfer
- light
- radio

37
Q

what are longitudinal waves? +example

A

waves in which the particles vibrate parallel to the direction of energy transfer
- sound

38
Q

what is the doppler effect?

A

the apparent change in frequency of a wave when there is relative motion between a source and an observer

39
Q

types of doppler effect {equations}

A
  1. source moving towards observer
    λs = v / fs
    λo = v - vs / fs
    fo = v / λo
    ∴ fo = v / v - vs fs
  2. when source is moving away from observer
    λo = v + vs / fs
    ∴ fo = v / v ± vs fs
40
Q

what is a red-shift?

A

looking for meaning

41
Q

what are electromagnetic waves?

A

a disturbance in the electric and magnetic fields space

42
Q

speed of light in a vacuum

A

c = 3.0 x 10^8 ms^-1

43
Q

electromagnetic spectrum

A
  • radio waves
  • microwaves
  • infrared
  • visible
  • ultraviolet
  • x-rays
  • gamma rays
    [this is in order of ROYGBIV]
    gamma to radio is increasing wavelength
    radio to gamma is increasing frequency
44
Q

similarities of electromagnetic waves

A
  • travel at a speed of 3.0 x 10^8 ms^-1 in free space
  • are transverse
  • are progressive (they transmit energy)
45
Q

what is polarisation?

A

this is when vibrations of a transverse wave are restricted to a single plane it doesn’t occur to longitudinal waves

46
Q

how can we polarise light?

A

by using a polaroid filter

47
Q

what is malus’ law?

A

states that the intensity of plane polarised light that passes through an analyser varies as the square of the cosine of the angle between the plane of the polariser and the transmission axis of the analyser
I = Io cos^2x

48
Q

what is superposition?

A

occurs when 2 or more waves of the same type meet

49
Q

principle of superposition

A

states that when 2 or more waves meet at a point, the resultant displacement is the algebraic sum of the displacements of the individual waves at the point

50
Q

constructive + in phase wave?
destructive + out of phase wave?

A
  • amplitude double
  • amplitude zero
51
Q

what is a stationary wave?

A

when 2 waves, which have the same speed, frequency and approx. the same amplitude, but travelling in opposite directions meet

52
Q

what is a node?

A

points on a stationary wave where particle displacement is zero

53
Q

what is an antinode?

A

points on a stationary wave where particle displacement is maximum. marks the amplitude of a stationary wave

54
Q

fundamental frequency for
first harmonic
second harmonic (first overtone)
third harmonic (second overtone)

A
  • fo = v / 2L
  • f1 = 2fo
  • f2 = 3fo
55
Q

nth harmonic for (n-1)th overtone

A

fn = n v / 2L

56
Q

formula for stationary waves in a closed pipe
- first harmonic
- third harmonic ( 1st overtone)
- fifth harmonic ( 2nd overtone)
- gen. formula

A

first harmonic - fo = v / 4L
third harmonic (1st overtone) - f1 = 3Fo
fifth harmonic (2nd overtone) - f2 = 5fo
general formula is,
fn = (2n - 1) v/4L

56
Q

formula for stationary waves in an open pipe
- 2nd harmonic (1st overtone)
- 3rd harmonic (2nd overtone)
- gen. formula

A

first harmonic - fo = v / 2L
2nd harmonic (1st overtone) - f1 = 2fo
3rd harmonic (2nd overtone) - f2 = 3fo
general formula is,
fn = n v / 2L

57
Q

comparison of progressive and stationary waves

A

p -crests and troughs move along the string
s - nodes and antinodes do not move along the string
p - all points have the same amplitude
s - amplitude of vibration varies with position along the string. its zero at a node, maximum at antinode
p - phase varies continuously along the wave
s - between adjacent nodes, all points of stationary wave vibrate in phase

57
Q

formula for end correction, c

A

fo = v/4 (L+c) [closed pipe]
fo = v/2 (L+2c) [open pipe]

58
Q

what is diffraction? +formulas

A

the spreading of a wave as it passes past an obstacle or gap
λ = a sinx
sinx = λ / a
sinx = nλ / a

59
Q

conditions for interference of light

A
  1. the sources must be very close together
  2. the screen / eyepiece must be as far away from the source as possible
  3. must meet and cross
59
Q

interference of light

A

occurs when similar waves from 2 coherent sources cross

59
Q

what is coherent?

A

sources produce waves having the same frequency

60
Q

what is monochromatic?

A

light of a single frequency

61
Q

where does superposition occur during a double slit?

A

where the beams overlap

62
Q

nb:

A

look at fringes and their conditions

63
Q

what is a diffraction grating?

A

a number or fine, equidistant closely spaced parallel lines of equal widths ruled on glass or polished metal by a diamond point

64
Q

types of diffraction grating

A

transmission - glass is used with ruled lines scattering incident light and are more or less opaque, spaces in between them transmit light and act as slits

reflection - lines are ruled on a polished metal and are opaque, while spaces in between them reflect light regularly and act as slits

65
Q

diffraction of light by diffraction grating formula

A

dsinx = nλ

PHYSICS (4 decks)

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