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S2 Flashcards > Physics Unit 2 And 3b > Flashcards

Physics Unit 2 And 3b Flashcards

1
Q

What is meant by a progressive wave?

A
  • A wave that carries energy from one point to another using vibrations
  • without transferring matter
  • can be either transverse or longitudinal
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2
Q

Distinguish between the two types of progressive waves, and give two examples of each

A

Transverse - the direction of the vibrations is perpendicular to the direction of wave propagation
- two examples of this are water waves and electromagnetic waves, i.e. light, x-rays, and micro

Longitudinal - the direction of the vibrations is parallel to the direction of wave propagation
- two examples of this are sound waves and ultrasonic waves

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3
Q

Define the terms “frequency”, “amplitude”, “speed” and “wavelength”

A

Frequency - the number of complete waves generated in one second
- measured in Hertz (Hz)

Amplitude - the distance of any given crest or trough
- from the undisturbed point of what is carrying the wave
- measured in metres

Speed - the distance moved by any point of the wave in one second
- measured in metres per second

Wavelength - the distance between any two consecutive crests or troughs of a waveform
- measured in metres
- represented by the Greek letter lambda (λ)

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4
Q

Describe the relationship between speed, frequency, and wavelength, form an equation and rearrange to find all three quantities

A

The frequency of a wave is constant in any given medium, and its speed and wavelength are inversely proportional, this can be written as:

To find speed;
v = fλ

To find frequency;
f = v/λ

To find wavelength;
λ = v/f

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5
Q

Describe the law of reflection and how water waves in a ripple tank are used to prove this

A

The angle of incidence = the angle of reflection
θi = θr

  • Straight water waves that hit a barrier normally are reflected back on themselves exactly
  • Straight water waves that hit a barrier incidentally are reflected from the normal at the same angle
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6
Q

Describe refraction and explain how water waves in a ripple tank show this

A

Refraction is the change in direction a wave undergoes as it crosses a boundary

  • water waves show this when travelling into different depths of water
  • frequency of waves is always constant
  • as waves travel from deep to shallow water their speed and wavelength decrease
  • as waves travel from shallow to deep water their speed and wavelength increase
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7
Q

State the echo principle, the equation and two applications of the echo principle

A
  • Reflection of sound waves off surfaces
  • works best against hard flat surfaces
  • twice the distance from the surface divided by the time taken to hear the echo
  • 2d/t
  • sonar and ultrasonic imaging are two modern applications of this
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8
Q

Define ultrasound, give the frequency of ultrasonic waves, and give 2 examples of application of ultrasound

A
  • any sound wave with a frequency that exceeds the range of audibility for humans (20 - 20,000Hz)
  • have a frequency of 20,000+Hz
  • used to measure foetal head diameter, as well as detect defects in metals
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9
Q

How are echoes and EM waves used in sonar

A
  • sonar systems send sound pulses to detect objects in the water
  • and electromagnetic waves are used to detect aircraft and other boats from under the water
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10
Q

List the members of the Electromagnetic Spectrum, and their respective wavelengths

A

All electromagnetic waves have a speed of 300,000,000m/s in a vacuum, with varying frequencies and wavelengths. In order of decreasing wavelength they are:

Radio - 1km - 1m in λ
Micro - 1cm in λ
Infra-red - 0.01mm in λ
Visible - 0.7μm - 0.4μm in λ
Ultra-violet - 0.1μm in λ
X-ray - 1nm in λ
Gamma - 0.01nm in λ

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11
Q

List some of the dangers attributed with electromagnetic waves

A
  • microwaves cause internal heating of body tissues
  • infra-red, or heat radiation causes skin to burn
  • certain wavelengths of ultraviolet can mutate nuclei of skin cells and cause cancer
  • intense visible light can damage the eyes
  • X-rays and gamma rays can be potentially cancer causing
  • although not reliably proven, it is believed that low frequency radio waves can affect peoples’ health, cause cancer, leukaemia, and other disorders
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12
Q

Where are angles of incidence and reflection/refraction measured from, and how is this point determined

A
  • They are measured from the normal
  • This is an imaginary line that is perpendicular to the reflective surface, or boundary
  • splits the incident ray and reflected/refracted ray at the point where they meet on the surface
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13
Q

Describe the properties of an image formed in a plane mirror

A
  • it is virtual
  • it is laterally inverted
  • it appears to be the same distance behind the mirror as the object is in front
  • it is the same size as the object
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14
Q

Describe how light is refracted as it travels between media

A
  • As light passes between media it changes speed, which causes it to bend
  • if travelling across an interface between a less dense medium and a more dense medium it speeds up, and bends towards the normal (i.e. air into glass)
  • if travelling across an interface between a more dense medium and a less dense medium it slows down, and bends away from the normal (i.e. glass into air)
  • there acronyms LTM (less towards more) and MAL (more away from less) can be used to help remember
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15
Q

What factors determine how much light is refracted

A
  • refraction is dependent on the change in speed of light
  • so the greater the speed before entering the medium will increase the amount of refraction
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16
Q

How is a prism used to disperse white light

A
  • as white light is shone through a prism it disperses
  • this creates a spectrum of all the colours white light is made up of
  • this spectrum is seen because all of the colours in white light travel at different speeds in glass
  • we know that refraction is dependent on change in speed, so we can conclude that;
  • since red is refracted least, it slows the least, and since violet refracts the most, it slows the most
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17
Q

Define “critical angle” and “total internal reflection”

A

Critical angle - the angle of incidence into a medium when the angle of refraction is exactly 90°
Total internal reflection (TIR) - when the angle of incidence exceeds the critical angle and no refraction takes place
- the ray of light is totally reflected inside the glass block

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18
Q

Describe how TIR occurs in 45° prisms and state one application of this

A
  • the critical angle for this type of prism is 42°
  • when a ray of light is shone through perpendicular to the prism it is turned through 90°
  • because at the glass-air interface the angle of incidence is 45° so TIR occurs, and the ray of light is reflected, meeting the second glass-air interface normally, and passing through without being refracted
  • this principle is used in periscopes, with 2 45° prisms being used to look over things
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19
Q

Describe and explain how optical fibres utilise TIR to enable long distance communication

A
  • An optical fibre is a very thin piece of glass that undergoes repeated TIR, trapping the light inside, even when it is bent
  • information such as computer data, telephone calls, and video signals are converted into tiny pulses of visible, or infra-red light, and transmitted long distances along the fibres
  • they are much cheaper than copper cables and can transmit much more information for the same diameter
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20
Q

Define what is meant by the “focal length” of a lens

A

The distance from lens to the principal focus (focal point)

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21
Q

Describe how the shapes and actions of a converging and diverging lens differ

A
  • a converging (convex) lens is widest at its midsection, whereas a diverging (concave) lens is thinnest at its midsection
  • parallel rays of light that travel through a converging lens meet at a point on the principal axis (focal point) whereas in a diverging lens they appear to meet on the principal axis at a point behind the lens
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22
Q

How does short-sightedness occur and what effect does this have on the sufferer

A
  • the eyes grow to be too long so that light entering the eye is focused at a point in front of the retina
  • this causes distant objects to appear blurry
  • it is corrected using a diverging lens
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23
Q

How does long-sightedness occur and what effect does this have on the sufferer

A
  • the eyes grow to be too short, or the lens is not thick enough to focus light on the retina, so images are focused at a point behind the retina
  • close-up objects appear blurry
  • corrected using a converging lens
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24
Q

Define “conductors” and “insulators”, and describe how they differ in terms of free electrons

A

Conductor - a material through which charge can easily move

Insulator - a material through which charge can not move

  • Current is the flow of charged particles (ions/electrons) in one direction
  • good conductors can be characterised as such because they contain delocalised electrons, i.e. metals, and these can flow throughout the structure freely and carry charge
  • insulators do not contain delocalised electrons, so charge can not flow through them, so they are poor conductors, i.e. plastic, rubber, and glass
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25
Q

Recall the two types of current, and how they are different

A

Electron flow - the actual direction of current flow within a conductor
- the direction of electron flow is from the negative terminal of a cell to the positive terminal, through the conductor
- as the electrons are repelled by the negative terminal, and attracted to the positive

Conventional current - the original concept of current flow, before the discovery of delocalised electrons
- the direction of conventional current is from the positive terminal of a cell to the negative terminal through the conductor
- it is marked on all circuit diagrams, and is the type of current many equations are based on

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26
Q

Describe how voltage and current are divided in series circuits

A
  • current is constant through all components
  • volatile is split between components
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27
Q

Describe how volatile and current are divided in parallel circuits

A
  • the voltage is constant between all components, as well as the power supply
  • current is divided between components
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28
Q

Recall the equations for charge flow and resistance, and state the units for each

A

Charge flow = current * time
Measured in Coulombs (C)

Resistance = voltage / current
Measured in Ohms (Ω)

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29
Q

How do you calculate the total resistance of resistors in a series circuit

A

R = ΣRn
Aka the sum of all the resistors in the circuit

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30
Q

How do you calculate the total resistance of resistors in parallel circuits

A

1/R = Σ1/Rn
Aka the sum of the reciprocal of each resistor is equal to the reciprocal of the total resistance

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31
Q

How do you calculate the total resistance of resistors in a circuit that has series and parallel sections

A
  • If n equal resistors of RΩ are connected parallel to one another, the total resistance is equal to R/n
  • if the values of n resistors are different you use the parallel resistors formula to find the reciprocal of ΣR

i.e.

Resistors of 12Ω, 8Ω, and 4Ω are connected parallel to one another, if this was replaced with one resistor of equal resistance, what value would it have?

1/R = 1/R1 + 1/R2 + 1/R3
1/R = 1/12 + 1/8 + 1/4
1/R = 11/24
R = 24/11
R = 2.182Ω

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32
Q

Describe Ohm’s Law and state the equation which shows this

A

At a constant temperature current and voltage through a conductor will be directly proportional

Voltage = Current x Resistance
V = IR

33
Q

Describe how you would test this practically

A
  • set up a circuit with an ammeter, voltmeter, and a switch
  • the switch is turned on and off quickly in order to maintain constant temperature
  • the voltage and current readings are taken, proving Ohm’s law
  • these results are graphed on a voltage-current graph, which has a straight line through the origin
34
Q

How does length of a wire affect resistance

A

As length increases so does resistance

35
Q

How would you test this practically

A
  • set up a circuit with a length of wire attached to a metre rule
  • have a crocodile clip on the other side of the circuit so that it can be closed at different lengths
  • attach an ammeter in series, and a voltmeter across the length of wire
  • record the results for voltage and current and use these to calculate the resistance at different lengths
  • plot a graph of these results in a graph with resistance on the y-axis and length on the x-axis
  • draw a line of best fit through these points through the origin
  • this shows how resistance and length are directly proportional
36
Q

List other factors affecting resistance (2)

A
  • material
  • CSA of the conductor
37
Q

Why does electrical current generate heat

A

Energy is released when atoms collide with free electrons within conductors

38
Q

Recall the two equations for electrical power and energy

A

Power = current x voltage
P = IV

Energy = power x time
E = Pt

39
Q

Define and explain the difference between a.c. and d.c.

A

Direct current (d.c.) only travels in one direction
Alternating current (a.c.) changes direction

  • note: as soon as a current changes direction, it becomes alternating
40
Q

What is the cost of electricity measured in and how is it calculated

A
  • Electricity cost is measured using the kilowatt-hour, and it is calculated by multiplying the power rating in kilowatts, by the time an appliance was used in hours
  • this is the equivalent of one unit of electricity
  • cost of electricity is calculated using the formula:
    Cost = number of units used x cost per unit
  • the number of units is the difference between the present meter reading and the previous reading
41
Q

Why are switches in single switch circuits described as breaker switches

A
  • when they are closed the two terminals in the cell are connected and current can flow
  • when they are open the circuit is “broken”
  • these switches are always placed on the positive (live) side of a circuit
42
Q

Describe how a dual-switch circuit works and give an example of where it may be used

A
  • in a dual-switch circuit there are two possible pathways for current to flow, and two switches
  • this means there is no definitive open or closed position for either switch
  • both switches must be facing in one direction for the terminals to connect and allow current to flow
  • this is used in lights that go down long corridors or up stairs, so that lights can be turned on/off from either end
43
Q

Recall the positions, colours, and functions of the wires in a 3-pin plug

A

Earth wire - located in the middle, it is a copper wire coated in yellow and green plastic
- allows a path for current to flow from the case of the device into the ground if there is a fault

Live wire - located in the bottom right, it is a copper wire coated in brown plastic
- allows current to flow into the circuit

Neutral wire - located in the bottom left, it is a copper wire coated in blue plastic
- completes the circuit formed by the live wire

44
Q

Why is earthing used in appliances with metal cases

A
  • Earthing is used in appliances with metal casings as if there is a fault and the live wire becomes loose it may touch the casing
  • this will allow current to flow through the casing, causing electrocution if touched
  • the Earth wire provides a pathway from the appliance to the ground via a low resistance copper wire connected to something under the ground such as a metal plate
45
Q

What is the function of the fuse in a plug

A
  • The fuse is a small piece of wire, connected to the live wire
  • it is designed to melt if the current in the wire gets too great
  • breaking the circuit and preventing electrocution
  • however this is not 100% safe, as the fuse can take up to 2 seconds to melt, which is still a big enough window for electrocution to happen
  • a current as small as 50mA can cause electrocution
46
Q

How are fuses selected

A
  • the common fuse sizes are 3A, 5A, and 13A
  • the current flowing through a circuit is calculated using I = P/V
  • then the next largest fuse is chosen
47
Q

What is double insulation and how is it used to protect users

A
  • when there are two layers of insulation separating someone from a live wire
  • often the plastic casing of the plug, and the plastic coating of the wire
  • this helps to prevent electrocutions, and make them less likely if one type of insulation breaks
48
Q

How would you use plotting compasses to find the shape and direction of the lines of flux around a bar magnet

A
  • place a bar magnet on a page and trace around it
  • place the compasses around the magnet
  • record the direction in which the compass points
  • this is the direction of the magnetic field lines
  • repeat this at varying distances with multiple compasses
  • draw lines through these points
  • this shows the shape and direction (N to S) of the magnetic field lines/lines of flux around the magnet
49
Q

Describe how the right-hand grip rule can be used to find the direction of a magnetic field in a current carrying wire, and in a coil of wire around a solenoid

A

Current carrying wire:
- grip the wire with your right hand
- with your thumb pointing in the direction of conventional current flow
- the direction the rest of your fingers wrap around the wire is the direction of the magnetic field

Coil of wire around a solenoid:
- grip the solenoid with your right hand
- wrap your fingers around the solenoid in the direction of conventional current flow
- the direction of your thumb is the direction of the magnetic field

50
Q

Recall and describe the factors that affect the strength of an electromagnet

A
  • the size of the current in the coil, greater current means stronger magnetic field
  • the number of coils in the wire, more coils means stronger magnet
  • the material of the core, poor conductor means weak magnet, strong conductor means strong magnet
  • Iron is used to make temporary electromagnets, steel is used to make permanent ones (SPIT)
51
Q

Recall the relationship between force, direction of magnetic field, and direction of conventional current, and how Fleming’s left hand rule is used to show this

A
  • force on a conductor in a magnetic field is perpendicular to the direction of both the current and magnetic field
  • Fleming’s left hand rule can be used to find the direction of all these variables if one is known
  • the thumb represents the force, the index finger is the direction of conventional current, and the middle finger is the direction of the magnetic field
52
Q

Describe the process of electromagnetic induction in and out of a coil connected to a centre-zero ammeter

A
  • current is induced when a magnet is moved into the coil
  • this causes the needle of the centre-zero ammeter to deflect in a direction
  • pulling the magnet out again causes the direction of current to be reversed
  • causing the needle to deflect in the other direction
  • and reversing the poles of the coils
  • no current is induced when the magnet is not moving
  • this is the basis for generating electricity
  • current can also be induced if the magnet is held stationary and the coil is moved
  • or if the magnet is rotated close to the coil
53
Q

List ways the size of the induced current can be increased

A
  • more coils in the wire
  • increasing the strength of the magnet
  • moving the magnet faster into and out of the coil
54
Q

Describe the process of electromagnetic induction between two coils of wire; where one is connected to a power supply and switch while the other is connected to a centre-zero ammeter

A
  • also known as mutual induction, and is the basis for transformers, which are used to change the size of ac voltages in household appliances
  • can be shown by placing two coils of wire next to each other
  • one coil (primary coil) is connected to a power supply
  • the neighbouring coil (secondary coil) is connected to a centre-zero ammeter
  • both are connected to an iron core, magnetically, but not electrically
  • when the switch is closed the needle flicks in one direction and then returns to zero
  • if the switch remains closed the needle remains at zero
  • when the switch is opened the needle flicks in the other direction then returns to zero
  • as long as the switch is open the needle remains at zero
55
Q

Why does this happen?

A
  • A changing magnetic field in the primary coil, links with the secondary coil, and induces a current to flow in the secondary coil
56
Q

Describe the structure of a simple ac generator

A
  • a coil of wire rotated between the poles of a magnet
57
Q

Describe the structure of a step-up and step-down transformer, and state the function of the core

A
  • a primary coil connected to an ac power supply
  • a secondary coil leading to an ac output
  • both wound around an iron core, connected magnetically but not electrically, within its magnetic field
  • a primary voltage drives an alternating current through the primary coil, producing a changing magnetic field. The magnetic field changes as current changes direction
  • the iron core is easily magnetised and carries the changing magnetic field from the primary coil to link the secondary coil
  • alternating voltage is induced in the secondary coil, causing an alternating current to flow
58
Q

What are key aspects about the function of transformers

A
  • transformers can only work with ac
  • in and output voltages and currents are all alternating
  • mains voltage is ac, which allows transformers to be used
59
Q

What is the difference between step-up and step-down transformers, and what is it dependent on

A
  • a step-up transformer, which increases voltage, has more turns in the secondary coil than the primary
  • a step-down transformer which decreases voltage has less turns in the secondary coil compared to the primary
  • the size of the output voltage is dependent on the number of coils of the secondary coils compared to the primary
60
Q

State the expression linking voltage, and number of turns in the primary and secondary coils (turns-ratio equation)
State the expression linking power to voltage and current in both transformers

A

Turns-ratio equation:

VS = N S
V P N P

  • transformers are 100% power efficient (power in = useful power out)
  • therefore, power between transformers can written as:

VSIS = VPIP

61
Q

Describe the role of transformers in transmission of electricity

A
  • Power stations generate electricity at 25,000 V
  • a step-up transformer beside the power station to step-up the voltage and consequently step-down the current reducing electrical energy wasted as heat energy in the overhead cables
  • electricity is sent through these at 400,000 V
  • this means that the current flowing in the overhead cables is relatively small and can be distributed long distances across country
  • transmitting small current greatly reduces heat lost in the cables, which in turn reduces the number of power stations needed
  • a step-down transformer close to domestic consumers to step the voltage down to 230 V for safe use in the home
  • Northern Ireland has just three major electricity generating stations
62
Q

Describe the main features of the solar system, including asteroids, comets, and moons

A
  • The Sun is our star and rests in the centre of the Solar system
  • It is composed primarily of Hydrogen and Helium
  • The 4 rocky planets (Mercury, Venus, Mars, and Earth) orbit closest to the Sun
  • The 4 gas giants (Jupiter, Saturn, Uranus, and Neptune) orbit farther away
  • The rocky planets and gas giants are separated by an asteroid belt
  • Asteroids and comets also orbit the Sun in this asteroid belt
  • Each planet has at least one moon, which orbits it, as well as the Sun
63
Q

Recall the order of the 8 planets from the Sun outwards

A

Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune

64
Q

What is gravity and how does it determine the orbital motion of artificial satellites, planets, and other celestial objects

A
  • Gravity is the force which pulls objects of smaller mass toward objects of lower mass
  • As objects move through space, they move with speed, but they are simultaneously pulled towards the Sun
  • The closer a planet is to the Sun, the stronger the Sun’s gravitational pull on it, and the faster the planet moves
  • The farther it is from the Sun, the weaker the Sun’s gravitational pull, and the slower it moves in its orbit
65
Q

Explain what is meant by a satellite, and state the two types

A
  • A satellite is any object that is in orbit around a planet
  • They fall into one of two categories; natural satellites, and artificial satellites

Natural satellite examples: moons, asteroids, comets

66
Q

State and describe some uses of artificial satellites

A
  • Communications – satellite television and phone calls
  • Earth observation - including weather forecasting, tracking storms and pollution, spying and satellite photography
  • Navigation - including the Global Positioning System (GPS)
  • Astronomy – looking into outer space from our solar system
67
Q

State and describe the two types of orbit these can take, and examples of when each is used

A

Types of orbit:
- Polar
- Geostationary

Description:

Polar:
- Polar orbits take the satellites over the Earth’s poles.
- The satellites travel as low as 200 km above sea level, so they must travel at about 8000 m/s to maintain orbit
- Polar orbits are often used for earth-mapping, as well as for some weather satellites.

Geostationary:
- Geostationary satellites take 24 hours to orbit the Earth, so the satellite appears to remain in the same part of the sky when viewed from the ground.
- These orbits are much higher than polar orbit, typically 36,000 km, so the satellites only travel at around 3 km/s
Geostationary orbits are used for communication and broadcast satellites.

68
Q

Explain how stars are formed

A
  • Stars are formed from giant clouds of hydrogen and dust, called nebulae, that have collapsed under their own gravity
  • As the nebula compresses under its own gravity the temperature and pressure increase
  • It becomes denser and rotates more rapidly, spiralling inwards, forming a hot core in the centre, known as a protostar
  • This process of dust and hydrogen collapsing and joining together due to gravity is known as accretion
  • As this process continues, the compressed hydrogen reaches a temperature of about 15 million OC
  • As this temperature nuclear fusion is able to happen, and a star is born
  • When the gas pressure exerted by nuclear fusion, and the pulling force of gravity are in equilibrium, the star is said to be in its main sequence (stable)
69
Q

Explain how planets are formed as a result

A
  • As the nebula begins to spin during accretion, debris in space, such as rock and ice begin to collide
  • As these masses begin to get larger, they generate their own gravitational field, and draw more debris towards them
  • Once the planet becomes large enough its gravity causes it to smooth out
  • As the planet continues to grow, it also begins to spin whilst in orbit of a star, pulling and holding more debris in orbit around it; these are called moons
70
Q

Recall the life cycle of an average sized star (our Sun) and describe each stage

A

Protostar - As the mass of the nebula falls together it gets hot, and forms the core of the star. This core is known as a protostar, and is kept hot by the fusion of hydrogen nuclei into helium nuclei

Main sequence star - The stage of a star’s life where it is stable. The force of thermal expansion is equal to the force of gravity pulling the gas and dust together

Red giant star - when all the hydrogen has been used up in fusion, larger and larger nuclei begin to form, and the star expands to become a red giant

White dwarf - when all nuclear reaction have taken place, the star begins to contract once more, to a size similar to its main sequence stage. This white dwarf fades and changes colour as it cools

Black dwarf - the theoretical final stage of a star’s life, where the white dwarf no longer emits significant heat or light, to the point that it is no longer visible

71
Q

Recall the life cycle of a massive star and describe each stage

A
  • Massive stars have the same life cycle as average sized stars until after the main sequence stage
  • After this they become red super giants. This stage is proceeded by an explosion which causes the outer layers of the star to be ejected, forming a supernova

Supernova - the penultimate stage of a massive star’s life cycle. This stage is relatively short, but at this stage the star will shine with the brightness of 10 billion suns
- After this the star will become a neutron star, or a black

Neutron star - extremely dense, and compact stars thought to be comprised almost entirely of neutrons. They range from about 1.2x to 2.0x the size of the Sun

Black Holes - a black hole is a great amount of matter packed into a relatively small amount of space. A black hole is formed when a massive star collapses in on itself. Because it is so heavy, but small, it has a massive gravitational field, which is so strong nothing can escape it; including EM radiation such as light, which is why they appear black

72
Q

How long ago did the universe form, and by what process

A
  • The Universe is believed to have formed roughly 13.8 billion years ago
  • It is believed to have been caused by what is known as the Big Bang
73
Q

Describe the Big Bang Theory of the Universe

A

The Bang Model is described as:
- The rapid expansion the Universe from an extremely hot and dense point (the singularity), followed by rapid cooling
- As the Universe continued to get larger it also cooled down, allowing protons, neutrons to form, eventually allowing them to combine to form nuclei
- As the Universe continued to cool electrons combined with these nuclei to form atoms of hydrogen
- The force of gravity acted on these atoms, pulling them together into bigger, and bigger clumps, until an estimated 400,000 years later, the first stars began to form

74
Q

State, and describe briefly, three pieces of evidence to support the Big Bang Theory

A
  • All other galaxies are moving away from us, with increasing speed, which is a proven characteristic of explosions; the fastest moving objects end up the furthest away from the initial impact
  • Light from distant stars is shifted toward the red end of the visible light spectrum (red-shift), and more distant stars have a greater red-shift, which is a sign that they are moving away, and a sign that the Universe is expanding
  • Scientists have been able to detect cosmic microwave background radiation (CMBR), which is heat energy from the Big Bang spread thinly across anywhere in the Universe at a temperature above -270OC
75
Q

Define the term “exoplanet” and describe how they are detected

A

Exoplanet - Any planet that orbits a star that is not the Sun
- They are often hidden by the glare of the distant stars they orbit, so require specialised methods to be observed

“Wobbly” Star method:
- Large planets cause their stars to orbit a bit off centre, as they are pulled to the side by the gravity between the star and the large planet
- This causes the star to appear as though it is wobbling from a distance
- This method can only be used to detect large exoplanets however

Transit method:
- This method is used to detect smaller, Earth-like exoplanets
- For this method astronomers look for the drop in brightness of a star as an exoplanet orbiting the star passes between it and Earth
- As the exoplanet moves across the front of the star, it limits the amount of the emitted light that is visible on Earth
- The dip in brightness is proof of the exoplanet

76
Q

State and describe some of the current limitations of space travel

A
  • The distances involved are too big. The nearest neighbouring star to Earth is Proxima Centauri, at a distance of about 4 x 1013km (40 trillion) away
  • With modern technology it would take 81,000 years to travel there, and at light speed, it would take 4.2 years
  • The logistics of carrying enough food, water, oxygen, and fuel for a round trip is impossible
  • Just making it out of Earth’s atmosphere is incredibly expensive because of the technology involved
  • Long periods of weightlessness is detrimental to the human body. It leads to muscle wasting and bone decay, and can prevent certain specialised cells working properly
  • Space radiation can cause cataracts as well as cancer
77
Q

Describe how composition of soil, and atmospheres, as well as how light passes through them, can be used as evidence of the ability to support life on other planets

A
  • The Earth’s atmosphere contains about 21 per cent oxygen as a result of photosynthesis. If we found evidence of oxygen in the atmosphere of another planet, it could indicate the presence of life forms.
  • It is possible to detect oxygen and other gases on other planets by studying the light reflected from planets.
  • The Search for Extra-Terrestrial Intelligence (SETI) uses radio telescopes to look for non-natural signals coming from space.
  • There are photographs of channels on Mars that may have been created by flowing water.
  • Space probes and landers are also looking for signs of extra-terrestrial life. Landers touch down on planets and take a soil sample, which is then analysed for evidence of life.
78
Q

Define a “light year” and prove that 1 light year = 9.46 x 1015m

A

Light year - the distance light travels in one year

Distance = speed x time

Speed of light = 300,000,000 m/s = 3 x 108 m/s

time = 1 year = 365 x 24 x 60 x 60 = 31,536,000 s

1 light year = 3 x108 m/s x 31,536,000 s = 9.46 x 10 15 metres

1 light year = 9.46 x 1015 m

S2 Flashcards (6 decks)

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