Flashcards in Component 1: Motion, Energy and Matter Deck (105)

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1

##
SI Quantities and Units...

Name - Mass

Symbol - ?

Name of unit - ?

Abbreviation - ?

###
SI Quantities and Units...

Name - Mass

Symbol - m

Name of unit - kilogram

Abbreviation - kg

2

##
SI Quantities and Units...

Name - Length

Symbol - ?

Name of unit - ?

Abbreviation - ?

###
SI Quantities and Units...

Name - Length

Symbol - l

Name of unit - metre

Abbreviation - m

3

##
SI Quantities and Units...

Name - Time

Symbol - ?

Name of unit - ?

Abbreviation - ?

###
SI Quantities and Units...

Name - Time

Symbol - t

Name of unit - second

Abbreviation - s

4

##
SI Quantities and Units...

Name - Electric Current

Symbol - ?

Name of unit - ?

Abbreviation - ?

###
SI Quantities and Units...

Name - Electric Current

Symbol - I

Name of unit - Ampere

Abbreviation - A

5

##
SI Quantities and Units...

Name - Amount of Substance

Symbol - ?

Name of unit - ?

Abbreviation - ?

###
SI Quantities and Units...

Name - Amount of Substance

Symbol - n

Name of unit - mole

Abbreviation - mol

6

##
Express as SI units...

Newton (N) =

Joule (J) =

Watt (W) =

###
Newton (N) = kgms^(-2)

Joule (J) = kgm^(2)s^(-2) = (Nm)

Watt (W) = kgm^(2)s^(-3) = (Js^(-1))

7

## What makes an equation homogeneous?

###
1. Two quantities can only be added or subtracted together if they have the same units - then the answer has the same units.

2. Units on both sides of the equation are the same.

8

## What is the difference between a scalar and vector quantity?

### A scalar quantity has magnitude. A vector quantity has magnitude AND direction.

9

## Examples of scalars...

### density, mass, volume, area, distance, length, speed, work, energy, power, time, resistance, temperature, pd, electric charge

10

## Examples of vectors...

### displacement, velocity, acceleration, force, momentum

11

## How to add and subtract vectors...

###
Nose-to-tail method.

(At AS, only need to + and - with vectors at right angles.)

12

## How to find horizontal (x) and vertical (y) components of vectors...

### Trigonometry.

13

## What is the symbol for density?

### ρ (rho)

14

## Which equation includes, Mass, Density and Volume?

###
ρ = m / V

(kgm^(3)) = (kg)(m^(3))

(Provided in exam formula booklet, so don't need to learn.)

15

## What is meant by the turning effect of a force?

### The turning effect of a force is also called a moment. It is dependant on the size of force, direction, and the distance between the pivotal point and where the force is applied. (A moment of a force can also be called its torque. Symbol: t )

16

## What is the principle of moments?

###
For a body to be in equilibrium under the action of a number of forces...

-The resultant moment about an point is 0.

(or)

-The sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about the same point.

17

## How do you calculate the moment of a force?

### moment of a force = force x perpendicular distance (from force to point).

18

## What is an object's 'centre of gravity'?

###
The mass of an object is spread out, however a point can be identified at which it can be considered all of its weight is acting. This point is the centre of gravity.

It is worth knowing the C of G for objects such as spheres, cylinders and cuboids.

19

## What does it mean if a body is said to be in equilibrium?

###
It is moving and rotating at a constant rate, or not moving at all.

Resultant force on an object = 0

Resultant moment about any point = 0

20

## How do you measure the density of a solid?

###
The two components required to calculate the density of a solid are mass and volume. Mass can be calculated using an electronic balance.

The volume of a regular shape can be calculated using equations e.g. cuboid v = lbh, cylinder v = (πd^(2)l) / 4

The volume of a irregular shape can be calculated by submerging the solid in a beaker of water. The increase in volume is the volume of the solid.

(Don't forget using resolutions to calculate uncertainties)

21

## How do you measure mass using the principle of moments?

###
Place a pivot at the C of G of the scale. Place a known mass (m), 'y' distance from the pivot. Move the unknown mass (M) away from the pivot on the opposite side until it reaches a distance (x), where the scale is balanced.

Mgx=mgy

(...) Mx=my

Allowing you to rearrange to find the unknown M.

22

## Details of displacement-time graphs...

###
displacement (y-axis), time (x-axis)

Gradient = Δx / Δt = velocity

Straight upwards slope = positive constant velocity

Curved upwards slope (gradient decreasing) = Increasing deceleration

Horizontal slope = Stationary

Curved downwards slope = Increasing acceleration (towards origin/opposite direction)

Straight downwards slope = positive constant velocity (towards origin/opposite direction)

23

## Details of velocity-time graphs...

###
velocity (y-axis), time (x-axis)

Gradient = Δv / Δt = Mean acceleration

Area between graph and x-axis = Displacement

Horizontal slope = constant velocity

Straight upwards slope = positive and constant acceleration

Straight downwards slope = Negative and constant acceleration.

24

## What does SUVAT stand for and what are the SUVAT equations?

###
s (sometimes 'x') - Displacement

u - Initial velocity

v - Final velocity

a - Acceleration

t - Time

v = u + at (Given in exam)

s = (1/2)(u+v)t (Given in exam)

s = ut + (1/2)at^(2) (Given in exam)

v^(2) = u^(2) + 2as (Given in exam)

s = vt - (1/2)at^(2) (Not provided in exam)

25

## How do you derive the SUVAT equations?

### https://www.youtube.com/watch?v=fmd_oIoPTjA

26

## How do you use the SUVAT equations?

###
1.) Choose which direction is positive and which is negative. Whether it be in the horizontal plane or vertical plane.

2.) Always write the quantities you know, to identify which SUVAT equation to use.

3.) Rearrange the equation so to have the value you are looking to find on one side and what you know on the other side.

4.) Insert the figures and calculate.

27

## Describe the motion of bodies falling in a gravitational field with and without air resistance...

###
All objects fall freely at the same acceleration when in the same gravitational field without air resistance, this acceleration due to gravity is called 'g'.

When an object is freely falling, if it is assumed that downwards is the positive direction, the acceleration will be g = 9.81 ms^(-2).

When an object is projected upwards the, if it is assumed upwards is the positive direction then acceleration will be -g = -9.81 ms^(-2)

So when using SUVAT equations on free falling objects or objects projected vertically upward, acceleration will be +g or -g, depending on the positive direction chosen.

(The addition of air resistance is discussed in the Dynamics chapter)

28

## Are the vertical and horizontal motion of a body moving freely under gravity independent of each other?

###
Yes.

When a ball is dropped from a point, it will reach the ground at the same time as an identical ball projected horizontally from the same point.

This is because, both balls accelerate downwards at the same rate (g), which is not impacted by the velocity of ball 2.

(Must be able to explain the motion of an object due to a uniform velocity in one direction and uniform acceleration in a perpendicular direction, and perform simple

calculations.)

29

## How do you measure g using freefall? (Equation)

###
You measure the time (t) it takes for an object to fall from a specific height (x).

Using x = ut + (1/2)at^(2), with u = 0, and a = g, the equation becomes:

x = (1/2)gt^(2)

g = (2x) / t^(2)

30

## How do you measure g using freefall? (Method)

###
Apparatus:

Electromagnet

AC Supply

Metre Rule

Steel Sphere

Hinged flap

Electronic timer

Method:

The steel sphere is held in place by the electromagnet, x m/cm/mm from the hinged flap, with the height measured by the metre rule. When the AC supply is switched off the timer starts and the ball falls, hitting the hinged flap, breaking the circuit and stopping the timer.

Analysis:

x is plotted against t^(2), and that means the gradient is (1/2)g. Doubling the gradient allows you to calculate g.

(There is systematic error in this method, due to short time delays between the the switch change on the AC supply and magnet / between the hinged flap and stopping the timer.)

31

## What is Newton's 3rd Law (N3)?

### If a body A exerts a force on a body B, the B exerts an equal and opposite force on A.

32

## What is the equation to calculate momentum from mass and velocity?

###
p = mv

(kgms^(-2)) = (kg)(ms^(-2))

(kgms^(-2)) = (Ns)

Velocity is a vector so state its direction as well as its magnitude.

33

## What is the principle of conservation of momentum?

### The vector sum of the momenta of the bodies in an isolated system (a system where no external forces act, and no particles leave or enter) is constant.

34

## What is the kinetic energy equation in terms of mass and velocity?

###
KE = (1/2)mv^(2)

(kg)(m(^2)s^(-2)) = (kg)(m(^2)s^(-2))

(kg)(m(^2)s^(-2)) = (J)

35

## What is the difference between elastic and inelastic collisions?

###
Elastic - Collisions which no kinetic energy is lost.

Inelastic - Collisions which kinetic energy is lost.

36

## What happens to momentum when a force is applied to an object? (When the mass remains constant).

###
Momentum changes when a force is applied to the object. The resultant force applied is directly proportional to the rate of change of momentum.

F(res) = Δp / Δt

(N) = (Ns) / (s)

37

## What makes forces an N3 pair?

###
1. The forces must be equal and opposite.

2. They must act on different bodies.

3. They must be the same kind of force.

38

## What is a normal force?

### If an object rests against a surface, the surface exerts a force on the object. The force is at right angles to the surface.

39

## What is friction?

###
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.

Static friction is the friction between two surfaces that are not in relative motion with each other.

Dynamic (aka Kinetic) friction is the friction between two surfaces that are in relative motion with respect to each other.

40

## What is air resistance?

### Air resistance (AKA Drag), is the force that oppose the relative motion of an object through the air.

41

## What is a free-body diagram? And why are they useful?

### A free-body diagram is used to show the forces on a particular object/body. Isolating the single object from all of the objects involved makes the forces much easier to identify.

42

## What is the equation for Force in terms of mass and acceleration? (When the mass of an object remains constant)

###
F = ma

(kg)(ms^(-2)) = (kg)(ms^(-2))

(kg)(ms^(-2)) = (N)

43

## What is weight defined as?

###
Weight is the gravitational force of an object. (In the absence of air resistance).

W = mg

(F = ma)

44

## Describe motion under gravity with air resistance.

###
Using the example of a skydiver.

1. When t = 0, acceleration will equal g. His weight force will equal mg throughout.

2. As the diver's velocity increases, the resultant force (air resistance) will increase and therefore acceleration will decrease.

3. This continues until the weight force (down) equals the resultant force downwards, at this point the diver is no longer accelerating and has reached 'terminal velocity'.

4. Opening a parachute will rapidly increase the resultant force, and will cause the diver to rapidly decelerate.

5. As the speed decreases, the resultant force will eventually reaches 0N and acceleration reaches 0.

45

## What is Newton's Second Law of Motion (N2)?

###
The rate of change of momentum on a body is directly proportional to the resultant force acting upon it.

For constant mass: a ∝ F

For constant force: a ∝ (1/m)

46

##
How would you investigate Newton's 2nd Law of Motion?

(Showing that a constant force gives a constant acceleration)

###
Apparatus:

(Similar set-up -> https://www.patana.ac.th/secondary/science/anrophysics/rocketphysics/images/airtrack.jpg)

Air track

Metal rider

Light gate (x2)

Meter rule

Thin thread

Low-friction pulley

Low mass object

Light shield (width Δx)

Method 1:

Using 1 light gate (gate 2).

1. Release rider from rest and use gate 2 and electronic timer to measure the time taken, Δt, for the light shield of width Δx, to cut off the light.

2. v = Δx / Δt, to calculate the velocity acquired by the rider after travelling a distance x from rest.

3. Repeat for a series of distances.

4. Plot a graph of v^(2) against x. If acceleration is constant, v and x are related by... v^(2) = u^(2) + 2ax. Therefore the graph will be a line of best fit through the origin. The gradient is 2a, allowing a to be calculated.

(x is the distance between the position of the midpoint of the light shield at the start of the light gate).

Method 2:

Using 2 light gates.

1. Release rider to right of gate 1 and use the electric timer to record the time t, to travel the distance between the two gates x.

2. Repeat for a series of x values.

3. Plot a graph of x against t. If acceleration is constant, x and t are related by... x = ut + (1/2)at. The gradient will be (1/2)a, allowing a to be calculated.

47

## How would you investigate Newton's 2nd Law of Motion? (Showing that acceleration is proportional to force)

###
Apparatus:

(Similar set-up -> https://www.patana.ac.th/secondary/science/anrophysics/rocketphysics/images/airtrack.jpg)

Air track

Metal rider

Light gate (x2)

Meter rule

Thin thread

Low-friction pulley

Low mass object

Light shield (width Δx)

Method:

1. Using technique 1 on the "How would you investigate Newton's 2nd Law of Motion?

(Showing that a constant force gives a constant acceleration)" flashcard, to measure acceleration. However instead of using a series of distances, use a variety of low masses to vary the weight force e.g. 1g, 2g, 10g, 15g.

2. In this experiment the mass needs to remain constant even though mass is being added to change the weight force. So it important no mass is added or taken from the system. At the start load all of the masses being used onto the rider, then move the masses one by one to the end of the thin thread. Therefore no mass is lost but the force is changing.

2. Plot a graph of a against the force. The line of best fit will have a positive gradient and go through the origin. So acceleration and force are directly proportional.

48

##
How would you investigate Newton's 2nd Law of Motion?

(Showing that acceleration is inversely proportional to mass)

###
Apparatus:

(Similar set-up -> https://www.patana.ac.th/secondary/science/anrophysics/rocketphysics/images/airtrack.jpg)

Air track

Metal rider

Light gate (x2)

Meter rule

Thin thread

Low-friction pulley

Low mass object

Light shield (width Δx)

Method:

1. Using technique 1 on the "How would you investigate Newton's 2nd Law of Motion?

(Showing that a constant force gives a constant acceleration)" flashcard, to measure acceleration. However instead of using a series of distances, apply a variety of masses onto the rider. (Rider typically as a mass of 150g and can take an additional 300g)

2. The force is kept constant as no additional mass is applied to the end of thin thread. (Remember to include this mass in the total mass of the system)

3. Plot a graph of a against 1/M. The line of best fit will have a positive gradient and go through the origin. So mass and acceleration are inversely proportional.

49

## What is energy? Is energy a scalar or vector quantity? What are the different types of energy?

###
Energy is the ability to do work. Work is done when a force moves its point of application.

Energy is a scalar quantity as it has magnitude but not direction.

Examples:

-Kinetic Energy (KE) - Energy due to motion.

-Heat/thermal Energy - Energy in the form of heat.

-Gravitational Potential Energy (GPE) - Stored energy in objects above the ground.

-Elastic Potential Energy (EPE) - Energy stored in a body by virtue of its deformation.

-Electrical Energy - Electrical energy is energy that is caused by moving electric charges. Since the electric charges are moving, this is a form of kinetic energy.

50

## What are the equations for 'Work Done'?

###
1.

W = Fx (Not provided in exam)

(Nm) = (N)(m)

(Nm) = (J)

(x = distance moved in direction of force)

2.

W = Fxcosθ (Provided in exam)

(Nm) = (N)(m)

(Nm) = (J)

Used when the force and displacement are not in the same direction. The addition of the cosθ is to find the component of the force in the direction of displacement.

3.

W = FvΔtcosθ

(Nm) = (N)(ms^(-1)(s)

(Nm) = (J)

(Not provided in exam)

4.

W = Energy Transferred (Not provided in exam)

(J) = (J)

e.g. If a force does 10J of work, 10J of energy is transferred.

51

## What is the principle of conservation of energy?

### The total energy in an isolated system is constant though it can be transferred within the system.

52

## What are the Kinetic Energy equations?

###
1.

KE = (1/2)mv^(2)

(kgm^(2)s^(-2)) = (kg)(m^(2))(s^(-2))

(kgm^(2)s^(-2)) = (J)

(Provided in exam)

2.

ΔKE = (1/2)mv^(2) - (1/2)mu^(2)

(kgm^(2)s^(-2)) = (kg)(m^(2))(s^(-2)) - (kg)(m^(2))(s^(-2))

(kgm^(2)s^(-2)) = (J)

(Provided in exam (ΔKE is written as Fx))

53

## What is the equation for Gravitational Potential Energy?

###
ΔGPE = mgΔh

(Provided in exam (ΔGPE written as ΔE))

54

## What are the equations for Elastic Potential Energy?

###
1.

EPE = (1/2)Fx

(kgm^(2)s^(-2)) = (kgms^(-2))(m)

(kgm^(2)s^(-2)) = (J)

(Not provided in exam)

2.

EPE = (1/2)kx^(2)

(kgm^(2)s^(-2)) = (kgs^(-2))(m^(2))

(kgm^(2)s^(-2)) = (J)

(Provided in exam (EPE written as E))

3.

(Not EPE but useful to explain the above two equations)

F = kx

(kgms^(-2)) = (kgs^(-2))(m)

(Not provided in exam)

3. can be plugged into 1. to find 2.

55

## What are the equations for Power?

###
1.

P = ΔE / t = W / t

(Js^(-1)) = (J)(s^(-1))

(Js^(-1)) = (W)

(Provided in exam)

2.

P = Fvcosθ

(kgm^(2)s^(-3)) = (kgms^(-2))(ms^(-1))

(kgm^(2)s^(-3)) = (W)

(Not provided in exam)

This can be can be derived by using W = FvΔtcosθ and P = W / t.

If F and v act in the same direction θ = 0 so P = Fv

56

## What symbol is commonly used to represent efficiency?

### η (eta)

57

## What are the efficiency equations?

###
1.

Efficiency (η) = (Useful energy transfer / Total energy input) * 100%

Useful energy is energy used for an object's main purpose. e.g. A lamp has an input of 100J, 25J are released as light and 75J are released as heat. As the main purpose of the lamp is light energy, the 25J will be the useful energy transfer.

2.

Efficiency (η) = (Useful power output / Total power input) * 100%

58

## What are the different types of force?

###
- Compressive

- Tensile

- Shear

59

## What is Hooke's Law?

###
The tension is directly proportional to the extension, provided that the extension is not too great.

F ∝ x

F = kx

(Not provided in exam)

k is known as the spring constant.

60

## What is tension?

### Tension is the force which an object exerts on external objects because it is being stretched.

61

## What is tensile stress?

###
If a bar, spring or wire etc with a cross-sectional area A, is pulled by a force F, its tensile stress, σ, is the ratio F/A.

So, σ = F/A

62

## What is tensile strain?

###
If a bar, spring or wire etc with length l is pulled by a force and increases in length by Δl then is tensile strain, ε, is the ratio of Δl/l.

So, ε = Δl/l

63

## For a material that obeys Hooke's law (Hookean), what is its Young modulus?

###
The Young Modulus, E = σ/ε.

This can also be written as E = Fl/AΔl

64

## What is the unit used to represent stress?

###
σ = F/A

Nm^(-2) = N/m^(2)

Nm^(-2) = Pa

Stress is measured in pascals, Pa.

65

## Which unit is used to represent strain?

### Strain has no units.

66

## What are typical values for E, σ and ε?

###
σ - 100 MPa

ε - 0.001

E - Rubber = 0.1 GPa

- Diamond = 1220 GPa

67

## Which graphs can be used to show the process of a material being stretched by a force?

###
Force-extension graph.

Stress-strain graph.

68

## What are the characteristics of a force-extension graph?

###
Force-extension graphs are used to show the work done when stretching a Hookean object. F is plotted against x. W = 1/2 Fx

So W is equal to the area underneath this graph.

69

## What does ductile mean?

### A ductile material can be drawn out. Into a wire for example.

70

## What does malleable mean?

### A malleable material can be hammered into shape.

71

## What are the characteristics of crystalline (polycrystalline) materials?

###
(The main crystalline materials needed for the course are ductile metals such as aluminium and copper).

Crystalline materials have a periodic structure called a lattice. The lattice particles in metals are positive ions - atoms which have lost one or more electrons. They are held together by a 'sea' of delocalised electrons which are free to move.

Another feature of the structure of these metals is the presence of irregularities within the lattice. One in every million planes or so, half a plane of atoms is misses - this is called an 'edge dislocation'. Point defects also occur when a missing or additional ion is present.

72

## Why do elastic and plastic deformation relate to edge dislocations?

###
When a ductile material is put under a low tension, the separation between the lattice ions is increased, this is elastic deformation. When the tension is removed the material will go back to its original position.

Irreversible rearrangement of particles causes plastic deformation. This occurs when edge dislocations within a material move under the influence of an applied force. Each ion only moves a small amount but the result is that the edge dislocation is moved to the grain boundary, and the material becomes elongated. The stress at which this happens is called the 'yield stress.'

73

## What are the characteristics of amorphous materials?

###
Amorphous solids, are rigid, but lack repeated periodicity in their structure. These substances do not show a sharp distinction between the solid and liquid states. Amorphous solids lack a characteristic geometry, have identical properties along all axes, have wide ranges over which they melt, and break to form curved or irregular shapes.

The most common examples of amorphous solids are glass and ceramics.

74

## What are the characteristics of polymeric materials?

###
A polymer is a substance whose molecules consist of long chains of identical sections called repeat units.

An example of a polymer is rubber. If a rubber molecule is placed under tension it stretches out. The force needed to stretch rubber is much less than a crystalline or amorphous material as bonds are not being stretched - just rotated.

75

## What are the features of a force-extension (or stress-strain) graph for a metal such as copper?

### The graphs starts linearly, the gradient of this is the Young modulus. When the graph starts curving this is the limit of proportionality and elastic limit, up to this point strains are elastic, beyond this point they are elastic. When the graph shows a large increase in strain compared to stress, this is the yield point. When the graph stops this is the breaking stress and the breaking point of the material.

76

## What are the features of a force-extension (or stress-strain) graph for a brittle material?

### The graphs starts linearly, the gradient of this is the Young modulus. The material then reaches its breaking point without plastically deforming, so the graph ends.

77

## What are the features of a force-extension (or stress-strain) graph for rubber?

###
Hooke’s law only approximately obeyed.

When a rubber band gets loaded by weights and then unloaded, it extends and retracts. The unloading curve is below the loading curve. This is called hysteresis. The area between the two curves represents the mechanical energy lost in the cycle. The energy is transferred to internal energy and lost as heat.

78

## How can you determine the Young modulus of a metal in the form of a wire?

###
In this experiment the tensile stress and strain of the material need to be calculated.

stress = F / A

strain = Δl / l

Method:

1. Measure the diameter of the wire using a micrometer or vernier calliper of resolution 0.01mm and use this to calculate A.

2. Measure the original length of the wire using a metre rule.

3. Add a small known mass.

4. Measure the new length.

5. Repeat 3 and 4, recording the results.

6. There should now be values for A, F, Δl and l. Use these to calculate the varying stress and strain.

6. Plot a graph of stress against strain and the gradient will be the Young modulus.

79

## How can you investigate the force-extension relationship for rubber?

###
Method:

1. Hang a rubber band over an elevated bar and measure its length.

2. Slowly add a known mass e.g. 100g, and measure the extension.

3. Repeat step 2 numerous times.

4. Slowly remove the masses and measure the reduction in length each time.

5. Plotting these results on a force-extension graph will show a hysteresis loop.

80

## What is dispersion?

### Dispersion is the separation of visible light into a spectrum. Can occur when using a diffraction grating or prism.

81

## What is a continuous spectrum?

###
A continuous spectrum consists of all wavelengths within a range. The spectrum formed from white light contains all colours/frequencies, and is known as a continuous spectrum.

Continuous spectra are produced by all incandescent solids and liquids and by gases under high pressure. This occurs with the dense gas of the surface of a star.

82

## What is a line spectrum?

###
A line spectrum consists of a series of individual wavelengths.

Gas under low pressure does not produce a continuous spectrum but instead produces a line spectrum. This arising from the passage of the emitted electromagnetic radiation through the tenuous atmosphere of the star.

83

## What is a black body?

### A black body is a body that absorbs all radiation which is incident upon it. It also emits more radiation at any wavelength than a non-black body in the continuous spectrum. Stars are good approximations of black bodies.

84

## What is absolute temperature? What is Celsius temperature?

### Absolute temperature (T) is temperature measured in Kelvin (K). Celsius temperature = T - 273.15.

85

## What is the Wien displacement law?

###
The peak wavelength emitted by a black body is inversely proportional to the absolute temperature of of the body.

λ(MAX) ∝ 1 / T

λ(MAX) = W / T

W = Wien constant (2.898x10^(-3) mK)

(Provided in exam)

86

## What is the Stefan-Boltzmann law?

###
The total power of the radiation emitted by a black body, per unit area is directly proportional to T^4.

P / A ∝ T^4

P = AσT^4

σ = Stefan-Boltzmann constant (5.67x10^(-8) Wm^(-2)K^(-4))

(Provided in exam)

87

## What is luminosity?

### The luminosity (L) of a star is the total energy emitted per unit time. Measured in Watts.

88

## What is intensity?

### The intensity (I) of radiation is the power per unit area incident on a surface at right angles to the radiation. (Wm^(-2)).

89

## What is the inverse square law?

###
The radiation from a source such as a star, spreads out as it moves further away. The bigger the area the radiation has to cover, the lower its intensity.

As light is emitted in all directions from sun, it can be said that there is a sphere of radiation moving out from the source.

So the intensity of the radiation at a given distance (r) from the source is equal to the luminosity divided by the surface area of the sphere at this distance.

I = L / 4πr^2

(Not provided in exam).

90

## What is an emission spectrum?

### A black body will show the whole spectrum whereas individual elements have their own line spectrum, making it possible to identify the gases present in different areas of the universe which emit light.

91

## What is an absorption spectrum?

### Sources which emit light at certain wavelengths only absorb certain wavelengths of light. So when white light is sent through the source, not all of it will make it through. The wavelengths not absorbed can be used to identify the elements which make up the source.

92

## How can the temperature of stars be identified?

### Observing which lines are present on the absorption spectrum and their prominence gives astronomers information of the temperature of the gas which is responsible for the absorption spectrum.

93

## What is multiwavelength astronomy?

###
Multiwavelength astronomy is astronomy which uses different regions of the electromagnetic spectrum to reveal different processes in the universe.

X-ray images only display very high temperature regions. UV also displays hotter regions and areas where young giant stars are forming. Infrared displays regions where stars are heating up dust clouds.

94

## What are elementary/fundamental particles?

### Elementary/fundamental particles are not made up by combinations of other particles.

95

## What are the first generation elementary particles?

###
Leptons (low mass elementary particles):

- Electron

- Electron Neutrino

Quarks (elementary particles not found in isolation):

- Up quark

- Down quark

(There are also 2nd and 3rd generation quarks but they are not needed for the exam)

96

## What are antiparticles?

### Each particle has a corresponding antiparticle with identical mass and equal + opposite charge.

97

## What are hadrons, baryons and meson?

###
A hadron is a combination of quarks and/or antiquarks.

A baryon is a combination of specifically 3 quarks or 3 antiquarks (antibaryon).

A meson is a combination of a quark or antiquark.

98

## What are the symbols, charges, baryon numbers, and lepton numbers for up and down quarks (and antiquarks)?

###
Name: Up quark

Symbol: u

Charge (in electrons): 2/3

Baryon: 1/3

Lepton: 0

Name: Down quark

Symbol: d

Charge (in electrons): -1/3

Baryon: 1/3

Lepton: 0

Name: Anti-up quark

Symbol: u (with a flat line above)

Charge (in electrons): -2/3

Baryon: -1/3

Lepton:0

Name: Anti-down quark

Symbol: d (with a flat line above)

Charge (in electrons): 1/3

Baryon: -1/3

Lepton:0

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##
What are the symbols, quark combination, charges, baryon numbers, and lepton numbers for baryons (needed for exam)?

###
Name: Proton

Symbol: p

Quark combination: uud

Charge (in electrons): 1

Baryon: 1

Lepton: 0

Name: Anti-proton

Symbol: p (with a flat line above)

Quark combination: uud (all anti quarks)

Charge (in electrons): 1

Baryon: -1

Lepton: 0

Name: Neutron

Symbol: n

Quark combination: udd

Charge (in electrons): 0

Baryon: 1

Lepton: 0

Name: Anti-neutron

Symbol: n (with a flat line above)

Quark combination: udd (all antiquarks)

Charge (in electrons): 0

Baryon: -1

Lepton: 0

Name: Delta plus

Symbol: Δ+

Quark combination: uud

Charge (in electrons): 1

Baryon: 1

Lepton: 0

Name: Anti-delta plus

Symbol: Δ+ (with a line above)

Quark combination: uud (all antiquarks)

Charge (in electrons): -1

Baryon: -1

Lepton: 0

Name: Delta minus

Symbol: Δ-

Quark combination: ddd

Charge (in electrons): -1

Baryon: 1

Lepton: 0

Name: Anti-delta minus

Symbol: Δ- (with a line above)

Quark combination: ddd (all antiquarks)

Charge (in electrons): 1

Baryon: -1

Lepton: 0

100

##
What are the symbols, quark combination, charges, baryon numbers, and lepton numbers for mesons (needed for exam)?

Name:

Symbol:

Quark combination:

Charge (in electrons):

Baryon:

Lepton: 0

###
Name: Pi plus

Symbol: π+

Quark combination: u(anti-d)

Charge (in electrons): 1

Baryon: 0

Lepton: 0

Name: Pi minus

Symbol: π-

Quark combination: (anti-u)d

Charge (in electrons): -1

Baryon: 0

Lepton: 0

Name: Pi zero

Symbol: π0

Quark combination: u(anti-u) or d(anti-d)

Charge (in electrons): 0

Baryon: 0

Lepton: 0

Name: Rho plus

Symbol: ρ+

Quark combination: u(anti-d)

Charge (in electrons): 1

Baryon: 0

Lepton: 0

Name: Rho minus

Symbol: ρ-

Quark combination: (anti-u)d

Charge (in electrons): -1

Baryon: 0

Lepton: 0

Name: Rho zero

Symbol: ρ0

Quark combination: u(anti-u) or d(anti-d)

Charge (in electrons): 0

Baryon: 0

Lepton: 0

101

## What are the symbols, quark combination, charges, baryon numbers, and lepton numbers for leptons (needed for exam)?

###
Name: Electron

Symbol: e-

Quark combination: (no quarks)

Charge (in electrons): -1

Baryon: 0

Lepton: 1

Name: Positron

Symbol: e+

Quark combination: (no quarks)

Charge (in electrons): 1

Baryon: 0

Lepton: -1

Name: Electron neutrino

Symbol: Ve

Quark combination: (no quarks)

Charge (in electrons): 0

Baryon: 0

Lepton: 1

Name: Anti-electron neutrino

Symbol: Ve (with a flat line above)

Quark combination: (no quarks)

Charge (in electrons): 0

Baryon: 0

Lepton: -1

102

## What are the 4 types of forces that particles experience?

###
Gravitational (Not needed for exam as it is negligible for sub-atomic particles)

Weak

Electro-magnetic

Strong

103

## What are the features of strong interaction?

###
- Particle decays have a very short lifetime (10^(-24)s)

- Interaction is likely to happen when particles collide.

- All particles involved are hadrons (no leptons)

- There is no change in quark flavour (There are the same number of up quarks and down quarks on the left and right of the equation. An antiquark is classed as a negative of its corresponding quark on the same side of the equation.)

104

## What are the features of electro-magnetic interaction?

###
- Particle decays have a short lifetime (10^(-15)s)

- All particles involved are charged or have charged components. (Does not involve any isolated neutrons, anti-neutrons, pi zeros or rho zeros etc).

- Interaction is likely to happen when particles collide.

- One or more photons may be emitted. (Symbol: γ (gamma)).

- There is no change in quark flavour.

105