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Flashcards in P2 - Living for the Future Deck (188):
1

What current does a photocell produce electricity with?

DC - like a battery.

2

What does DC mean?

The current flows the same way round the circuit at all times.

3

What are photocells made of and why?

Silicon - a semi-conductor. When sunlight falls cell, silicon atoms absorb some energy, knocking loose some electrons. These flow around a circuit - electricity.

4

What do curved mirrors do to sunlight and how can it be used to generate electricity?

Curved mirrors focus Sun's light and heat. Used as solar oven & large mirrors or combo of small can be used to generate steam to produce electric. Most effective if they track sun's movement across sky. Pointed directly at sun means maximum amount of light and heat.

5

What is passive solar heating?

Energy from Sun is used to heat something directly.

6

What does the current and output of a photocell depend on?

Its surface area (bigger = more electricity). Intensity of the light. Distance from the light source.

7

How do solar water heaters use passive solar heating?

Glass lets heat and light from sun in which is absorbed by black pipes and heats up water which can be used for washing or pumped to radiators to heat building.

8

What are the advantages of photocells?

No moving parts - sturdy, low maintenance and last a long time. No need for power cables or fuel. It's renewable and doesn't pollute environment.

9

What does wind power involve?

Putting loads of wind turbines up in exposed places - like moors, coasts and out at sea. Sun's energy heats atmosphere causing convection currents, wind. Turbines convert kinetic energy to electric. Blades turn a generator.

10

How does passive solar heating work?

Glass lets in heat & light from sun, which is absorbed by things in a room so they heat up. Light has short wavelength so it can pass through glass but heated things emit infrared radiation of longer wavelength, which can't escape through glass - reflected back instead.

11

What are the disadvantages of photocells?

No sunlight = no power

12

What are the advantages of wind power?

Cheap to run, tough and reliable, wind is free. Doesn't produce any polluting waste and it is also renewable.

13

What are the disadvantages of wind power?

1500 turbines needed to replace 1 coal station. Visual pollution, noise pollution, wind may not be fast enough, impossible to increase supply if extra demand, need to be spaced out - windy areas, expensive to set up - especially at sea.

14

What is the 1st stage in a power station?

To use the fuel to produce heat which then generates steam - this is the job of the boiler.

15

What is the 2nd stage in a power station?

The moving steam drives the blades of a turbine.

16

What is the 3rd stage in a power station?

Rotating movement from turbine is converted into electricity by generator (using electromagnetic induction)

17

What are the advantages of fossil fuels?

  • These burn to release energy.
  • At moment, readily available, but finite.
  • Concentrated source of energy (a little gives a lot)

18

What are the advantages and disadvantages of biomass?

  • Can be burnt directly or fermented to produce methane that's also burnt.
  • Renewable and more can quickly be made.
  • Carbon dioxide is produced but plants also take it to grow - carbon neutral.
  • No need to import.

19

What is electromagnetic induction?

Creation of a voltage (and maybe current) in a wire experiencing a change in magnetic field.

20

What is the dynamo effect?

Using electromagnetic induction to transfrom kinetic energy into electrical energy.

21

What are two situations where you get EM induction?

An electrical conductor moves through a magnetic field. And magnetic field through an electrical conductor changes.

22

What can you do to get a bigger voltage and current?

Increase magnet strength, number of turns on coil and speed of movement.

23

What is the frequency of AC electrical supplies?

Number of cycles per second and is measured in Hertz (Hz) which means coil in the generator is rotating a certain number of times per second.

24

How do generators work?

Rotating a coil in a magnetic field. Every half turn, current in coil swaps direction and produces AC. Turning coil faster produces more peaks and higher voltage and current.

25

What happens to electricity before it is sent throughout the country?

Voltage is increased to 400,000V which keeps current low meaning less wasted energy because heat of the cable is reduced.

26

How is electricity brought down to a safe voltage?

Using a step-down transformer scattered around towns. Transformers only work with AC.

27

What is the equation to calculate total energy input?

useful energy output + waste energy output

28

How is efficiency calculated?

(Useful energy output ÷ total energy input) x100

29

What is power measured in?

Watts (W) or kilowatts (kW) - where 1 watt means 1 joule per second

30

What is the equation for power (W)?

Voltage (V) x Current (A)

31

What is a Kilowatt Hour?

The amount of electrical energy converted by a 1kW appliance left on for 1 hour.

32

How is energy supplied calculated?

Power (in kW) x Time (Hours)

33

What are the advantages of using off-peak electricity?

Cost effective for the electrical company - power stations can't be turned off so it's good if there is demand. Cheaper for the consumer.

34

What are the disadvantages of using off-peak electricity?

Increased risk of fires with unsupervised appliances. Start fitting routine around cheap rate hours.

35

How does the greenhouse effect regulate the Earth's temperature?

Earth absorbs short wavelength EM radiation from Sun. Warms Earth's surface & some is emitted back out to space. Emitted waves are usually longer. Lots of infrared absorbed by atmospheric gases & re-radiate heat back towards Earth. Acts as an insulating layer.

36

What factors are causing CO2 levels to rise?

  • People use more energy, e.g. in cars which need burned fossil fuels which release CO2
  • Land needed - trees chopped so less absorbed and more released from burning
  • Respiration
  • Volcanic eruptions.

37

What factors are causing methane levels to rise?

  • Cattle farming increased to feed population.
  • Decaying waste is increasing.
  • Methane released naturally by volcanoes, wetlands and animals.

38

What factors are causing water vapour levels to rise?

  • Most from natural sources like oceans, seas, river and lakes.
  • Increase in global temperature
  • Power stations

39

What can a change in temperature cause?

  • Different weather patterns, including extreme weather.
  • Hurricanes form more often because there will be more hot water where hurricanes normally form.
  • Food production, too, with places made unsuitable to grow.

40

What human actions can cause a change to the weather/temperature?

Rising CO2 caused by humans affects the greenhouse effect, hence causing global warming. Soot and gases produced by factories reflect heat which causes an increase in local temperatures.

41

What happens when radiation causes ionisation?

The radiation causes atoms to lose or gain electrons turning the atoms into ions. Positive ions are formed when ions lose electrons. Negative ions are formed when atoms gain electrons.

42

Describe the properties of alpha particles…

Relatively big, heavy and slow moving (2 protons and 2 neutrons). Stopped very quickly due to size. Don't penetrate far into materials. Strongly ionising.

43

Why is gamma better for sterilising medical instruments?

Gamma kills all the microbe. It is better than boiling because plastic ones may get damaged. It needs to be a strongly radioactive source that’s lasts long so it doesn't need replacing often.

44

What determines a radiation's ionising power?

How far it can penetrate materials. The further the radiation can penetrate before hitting an atom, the less ionising it is.

45

What natural actions can cause a change to the weather/temperature?

Ash and gases from volcanoes can reflect radiation back into space, causing Earth to cool down. Changes in our orbit around the sun can cause ice ages.

46

What happens when radiation enters human cells?

It can ionise molecules and damage DNA which causes mutations in the cell that could lead to cancer. Very high doses can kill cells completely.

47

Describe the properties of beta particles…

Just electrons. Small and move quite fast. Penetrate moderately before colliding so they are moderately ionising but can be stopped by a few mm of aluminium.

48

Name two ways beta radiation can be used…

Medical tracers and thickness control.

49

How is beta used in thickness control?

When radiation goes down, paper has become too thick so rollers make it thinner. If it goes up, paper is too thin. Beta used - partially blocked by cardboard - if all went through, wouldn't change reading at all.

50

Describe the properties of gamma particles…

Type of EM radiation. No mass and no charge. Penetrates long way, weakly ionising. Stopped by very thick concrete or few cm of lead. The nucleus of alpha/beta may need to get rid of extra energy - emits gamma.

51

How is beta radiation used in tracers?

Once inside body, an external radiation detector converts the reading into a TV display showing where the strongest readings are from. Can show if body works properly. Beta used - passes through body and only radioactive for a few hours.

52

How is gamma used to kill cancer?

Rays are directed carefully at the cancer and is at the right dosage to kill the cancer without harming normal cells

53

What can alpha radiation be used in?

Smoke detectors - They have weak source of radiation and 2 electrodes. The radiation ionises the air and a current flows between the electrodes. In a fire, the smoke absorbs radiation - the current stops and sounds the alarm.

54

How is gamma used in non-destructive testing?

E.g. airlines check turbine blades in engines by directing gamma at them. If too much gets through to the detector, the blade is cracked or there's a welding fault.

55

What happens to produce nuclear power?

Nuclear fission - atoms in the nuclear fuel are split in 2. Water is added as a coolant to take away the heat and this is used to create steam to drive a turbine and generator.

56

What are the advantages of nuclear power?

Lots of energy made without releasing lots of CO₂. More energy is released - less uranium produces more. Fuel is relatively cheap and plenty of uranium is left in the ground.

57

What are the disadvantages of nuclear power?

Stations are expensive to build and maintain. Takes longer to start up nuclear power stations than fossil. Processing uranium causes pollution. Leaks are a risk. Disposing of radioactive waste. Decommissioning is expensive. Uranium is non-renewable.

58

What safety rules are there for working with radiation?

Full protective suits prevent radioactive particles being inhaled, lodging on skin/under fingernails. Lead-lined suits or barriers and thick lead screens shield workers from gamma in highly radioactive areas. Remote controlled robotic arms used.

59

How can low level radioactive waste be disposed of?

Like paper, gloves, clothing, syringes can be disposed of by burying it in a secure landfill

60

How can low level radioactive waste be disposed of?

Often sealed into glass blocks, then in metall canisters and then buried deep underground. Stays highly radioactive for tens of thousands of years.

61

What force is acting on everything in the solar system?

Gravitational attraction - pulls everything in Universe towards everything else.

62

What is circular motion and centripetal force?

Circular motion is always caused by a force towards the centre of the circle. For planets, moon etc in an orbit, this force is gravity. A force that causes a circular motion is called a centripetal force.

63

How was the asteroid belt formed?

When the Solar System was forming, rocks betweeen Mars and Jupiter didn't form a planet due to Jupiter's gravity interfering . This left millions of asteroids - rubble and rock - measuring up to 1000km in diameter.

64

What are meteors?

Rocks or dust that enters the Earth's atmosphere an burn up - so we see shooting stars. If it doesn't burn up, and hits Earth, they are meteorites.

65

What can happen if a meteorite hits Earth?

Fires can start, hot rocks and dust thrown in air, craters. Dust and smoke can block out sunlight causing climate change (species extinct).

66

How can we tell that asteroids have collided with Earth in the past?

Layers of unusual elements in rocks and sudden changes in fossil numbers between adjacent layers of rock, as species suffer extinction.

67

How do comets orbit?

Balls of rock, dust and ice orbit in elongated ellipses. Approaching sun, ice melts and creates tail of gas and debris. Speed up as they approach sun because Sun's graviational pull increases as it gets closer.

68

What are NEOs?

Near-Earth Objects - asteroids or comets which might be on a collision course with the Earth.

69

How are NEOs monitored?

Astronomers use powerful telescopes and satellites to search and monitor. When found, they can calculate the objects trajectory. Can be difficult to spot - they are small, dark and many have unusual orbits.

70

What happens if an NEO is heading for Earth?

Small NEOs would burn up harmlessly. Enough warning - may be able to deflect it. Eploding a bomb in, on or close to it might nudge it off course.

71

How do scientists think our moon was formed?

When our planet collided side-on with Earth. A Mars-sized planet. In the heat, dense iron cores merged to form Earth's core and less dense material ejected. This orbited Earth and came together to be the Moon.

72

What evidence is there to support the theory of the moon's formation?

The moon has a lower density than Earth and doesn't have a big iron core like Earth. Moon rocks contain few substances which evaporate at low temperatures - suggesting the Moon formed from hot material.

73

What is a light year?

The distance that light travels through a vacuum in one year. It is a measure of DISTANCE!

74

What are black holes?

When a really big star explodes. Have very large mass, small volume and very high density. Not visible - even light can't escape gravitational pull.

75

How can astronomers observe black holes?

Using x-rays emitted by hot gases from other stars as they spiral into the black hole.

76

What are the issues with manned spacecraft?

Have to carry loads of food, water and O₂, have to shield people from radiation, low gravity causes muscle wastage and loss of bone tissue. Psychologically stressful - same people in a small space for ages.

77

What are the advantages of unmanned space probes?

No need to carry food, water, oxygen. Withstand extreme conditions humans can't. More instruments fitted instead of people. Cheaper, less spent on safety. In a crash, no one gets hurt.

78

What are the disadvantages of unmanned space probes?

Probes can’t think for themselves. Spacecraft can't do maintenance or repairs whereeas people can.

79

How is data from spacecraft sent back to earth?

From distant objects: data needs to be beamed using radio waves. From nearer objects: probes or people could collect samples and physically bring them back to Earth.

80

What does measurement of red shift suggest?

That all distant galaxies are moving away from us very quickly - and it's all the same result whichever direction you look in.

81

What is the relationship between red shift and more distant galaxies?

More distant galaxies have greater red-shifts than nearer ones. This means more distant galaxies are moving away faster than nearer ones - the Universe is expanding.

82

What is cosmic background radiation?

Scientists can detect low frequency microwave radiation coming from all directions and parts of the Universe. It is strong evidence of the Big Bang. As the Universe expands and cools, the CBR cools and drops in frequency.

83

What did the Copernican model state?

That the Earth and planets all orbited the Sun which is at the centre of the universe, in perfect circles. It is a heliocentric model (sun at centre).

84

What evidence did Galileo find to support Copernicus?

Using telescope (new invention) saw stars in line near planet. Stars never moved, seemed to be carried along with planet (Jupiter). Suggested not stars, but moons. Showed not all was in orbit around Earth - Ptolemaic wrong.

85

What did Galileo notice about Venus?

Venus had phases. Amount Venus lit by Sun changed over time. Ptolemaic theory meant changes would be small, Venus would always be infront of Sun, but Copernican: Venus could move in front & behind Sun, changes would be big - like Galileo saw.

86

What did the Ptolemaic model suggest?

That everything orbited Earth in perfect circles. Also known as geocentric model. Ancient Greeks accepted theory in the 1500s until Copernican model put forward.

87

How is a protostar formed?

Gravity makes the gas an dust used to form stars spiral together. Gravitational energy has been converted into heat energy so the temperature rises.

88

How is the main sequence star formed?

When temperature gets high enough, hydrogen nuclei undergo thermonuclear fusion - form helium nuclei & gives out heat & light. Star enters long stable period where heat created by fusion provides outward pressure to balance gravity pulling everything inwards. Typically lasts several billion years.

89

How is a red giant formed?

Hydrogen begins to run out and the star then swells in to a red giant - it becomes red because the surface cools.

90

How is a planetary nebula formed?

A small-to-medium-sized star like the Sun then becomes unstable and ejects its outer layer of dust and gas as a planetary nebula.

91

What is a white dwarf?

The planetary nebula leaves behind a hot, dense solid core - a white dwarf - which just cools down and eventually fades away.

92

What leads to a supernova?

Big stars form red supergiants - start to glow brightly again as they undergo more fusion & expand & contract several times, forming heavier elements in various nuclear reactions. Eventually they explode - supernova.

93

How are neutron stars formed?

Exploding supernova throws outer layers of dust and gas into space, leaving very dense core called a neutron star. If star is big enough, becomes black hole.

94

DC - like a battery.

What current does a photocell produce electricity with?

95

The current flows the same way round the circuit at all times.

What does DC mean?

96

Silicon - a semi-conductor. When sunlight falls cell, the silicon atoms absorb some of the energy, knocking loose some electrons. These then flow round a circuit - electricity.

What are photocells made of and why?

97

Curved mirrors focus Sun's light and heat. Used as solar oven & large mirrors or combo of small can be used to generate steam to produce electric. Most effective if they track sun's movement across sky. Pointed directly at sun means maximum amount of light and heat.

What do curved mirrors do to sunlight and how can it be used to generate electricity?

98

Energy from Sun is used to heat something directly.

What is passive solar heating?

99

Its surface area (bigger = more electricity). Intensity of the light. Distance from the light source.

What does the current and output of a photocell depend on?

100

Glass lets heat and light from sun in which is absorbed by black pipes and heats up water which can be used for washing or pumped to radiators to heat building.

How do solar water heaters use passive solar heating?

101

No moving parts - sturdy, low maintenance and last a long time. No need for power cables or fuel. It's renewable and doesn't pollute environment.

What are the advantages of photocells?

102

Putting loads of wind turbines up in exposed places - like moors, coasts and out at sea. Sun's energy heats atmosphere causing convection currents, wind. Turbines convert kinetic energy to electric. Blades turn a generator.

What does wind power involve?

103

Glass lets in heat & light from sun, which is absorbed by things in a room so they heat up. Light has short wavelength so it can pass through glass but heated things emit infrared radiation of longer wavelength, which can't escape through glass - reflected back instead.

How does passive solar heating work?

104

No sunlight = no power

What are the disadvantages of photocells?

105

Cheap to run, tough and reliable, wind is free. Doesn't produce any polluting waste and it is also renewable.

What are the advantages of wind power?

106

1500 turbines needed to replace 1 coal station. Visual pollution, noise pollution, wind may not be fast enough, impossible to increase supply if extra demand, need to be spaced out - windy areas, expensive to set up - especially at sea.

What are the disadvantages of wind power?

107

To use the fuel to produce heat which then generates steam - this is the job of the boiler.

What is the 1st stage in a power station?

108

The moving steam drives the blades of a turbine.

What is the 2nd stage in a power station?

109

Rotating movement from turbine is converted into electricity by generator (using electromagnetic induction)

What is the 3rd stage in a power station?

110

  • These burn to release energy.
  • At moment, readily available, but finite.
  • Concentrated source of energy (a little gives a lot)

What are the advantages and disadvantages of fossil fuels?

111

  1. Can be burnt directly or fermented to produce methane that's also burnt.
  2. Renewable and more can quickly be made.
  3. CO2 is produced but plants also take it to grow - carbon neutral.
  4. No need to import.

What are the advantages and disadvantages of biomass?

112

Creation of a voltage (and maybe current) in a wire experiencing a change in magnetic field.

What is electromagnetic induction?

113

Using electromagnetic induction to transfrom kinetic energy into electrical energy.

What is the dynamo effect?

114

An electrical conductor moves through a magnetic field. And magnetic field through an electrical conductor changes.

What are two situations where you get EM induction?

115

Increase magnet strength, number of turns on coil and speed of movement.

What can you do to get a bigger voltage and current?

116

Number of cycles per second and is measured in Hertz (Hz) which means coil in the generator is rotating a certain number of times per second.

What is the frequency of AC electrical supplies?

117

Rotating a coil in a magnetic field. Every half turn, current in coil swaps direction and produces AC. Turning coil faster produces more peaks and higher voltage and current.

How do generators work?

118

Voltage is increased to 400,000V which keeps current low meaning less wasted energy because heat of the cable is reduced.

What happens to electricity before it is sent throughout the country?

119

Using a step-down transformer scattered around towns. Transformers only work with AC.

How is electricity brought down to a safe voltage?

120

useful energy output + waste energy output

What is the equation to calculate total energy input?

121

(Useful energy output ÷ total energy input) x100

How is efficiency calculated?

122

Watts (W) or kilowatts (kW) - where 1 watt means 1 joule per second

What is power measured in?

123

Voltage (V) x Current (A)

What is the equation for power (W)?

124

The amount of electrical energy converted by a 1kW appliance left on for 1 hour.

What is a Kilowatt Hour?

125

Power (in kW) x Time (Hours)

How is energy supplied calculated?

126

Cost effective for the electrical company - power stations can't be turned off so it's good if there is demand. Cheaper for the consumer.

What are the advantages of using off-peak electricity?

127

Increased risk of fires with unsupervised appliances. You also start fitting your routine around the cheap rate hours.

What are the disadvantages of using off-peak electricity?

128

Earth absorbs short wavelength EM radiation from Sun. Warms Earth's surface & then some is emitted back out to space. Emitted waves are usually longer. Lots of infrared absorbed by atmospheric gases &; re-radiate heat back towards Earth. Acts as an insulating layer.

How does the greenhouse effect regulate the Earth's temperature?

129

People use more energy, e.g. in cars which needs burned fossil fuels which releases carbon dioxide. Land is needed, meaning trees are chopped so less is absorbed and more is released from burning. Respiration and volcanic eruptions.

What factors are causing Carbon dioxide levels to rise?

130

Cattle farming increased to feed population. Decaying waste is increasing, causing levels to. Methan is released naturally by volcanoes, wetlands and animals.

What factors are causing methane levels to rise?

131

Most comes from natural sources like oceans, seas, river and lakes. Increase in global temperature could increase water vapour. Power stations also produce vapour.

What factors are causing water vapour levels to rise?

132

Different weather patterns, including extreme weather. Hurricanes will form more often because there will be more hot water where hurricanes normally form. Food production, too, with places made unsuitable to grow.

What can a change in temperature cause?

133

Rising carbon dioxide caused by humans affects the greenhouse effect, hence causing global warming. Soot and gases produced by factories reflect heat which causes an increase in local temperatures.

What human actions can cause a change to the weather/temperature?

134

The radiation causes atoms to lose or gain electrons turning the atoms into ions. Positive ions are formed when ions lose electrons. Negative ions are formed when atoms gain electrons.

What happens when radiation causes ionisation?

135

Relatively big, heavy and slow moving (2 protons and 2 neutrons). Stopped very quickly due to size. Don't penetrate far into materials. Strongly ionising.

Describe the properties of alpha particles…

136

Gamma kills all the microbe. It is better than boiling because plastic ones may get damaged. It needs to be a strongly radioactive source that’s lasts long so it doesn't need replacing often.

Why is gamma better for sterilising medical instruments?

137

How far it can penetrate materials. The further the radiation can penetrate before hitting an atom, the less ionising it is.

What determines a radiation's ionising power?

138

Ash and gases from volcanoes can reflect radiation back into space, causing Earth to cool down. Changes in our orbit around the sun can cause ice ages.

What natural actions can cause a change to the weather/temperature?

139

It can ionise molecules and damage DNA which causes mutations in the cell that could lead to cancer. Very high doses can kill cells completely.

What happens when radiation enters human cells?

140

Just electrons. Small and move quite fast. Penetrate moderately before colliding so they are moderately ionising but can be stopped by a few mm of aluminium.

Describe the properties of beta particles…

141

Medical tracers and thickness control.

Name two ways beta radiation can be used…

142

When radiation goes down, paper has become too thick so rollers make it thinner. If it goes up, paper is too thin. Beta used - partially blocked by cardboard - if all went through, wouldn't change reading at all.

How is beta used in thickness control?

143

Type of EM radiation. No mass and no charge. Penetrates long way, weakly ionising. Stopped by very thick concrete or few cm of lead. The nucleus of alpha/beta may need to get rid of extra energy - emits gamma.

Describe the properties of gamma particles…

144

Once inside body, an external radiation detector converts the reading into a TV display showing where the strongest readings are from. Can show if body works properly. Beta used - passes through body and only radioactive for a few hours.

How is beta radiation used in tracers?

145

Rays are directed carefully at the cancer and is at the right dosage to kill the cancer without harming normal cells

How is gamma used to kill cancer?

146

Smoke detectors - They have weak source of radiation and 2 electrodes. The radiation ionises the air and a current flows between the electrodes. In a fire, the smoke absorbs radiation - the current stops and sounds the alarm.

What can alpha radiation be used in?

147

E.g. airlines check turbine blades in engines by directing gamma at them. If too much gets through to the detector, the blade is cracked or there's a welding fault.

How is gamma used in non-destructive testing?

148

Nuclear fission - atoms in the nuclear fuel are split in 2. Water is added as a coolant to take away the heat and this is used to create steam to drive a turbine and generator.

What happens to produce nuclear power?

149

Lots of energy made without releasing lots of CO₂. More energy is released - less uranium produces more. Fuel is relatively cheap and plenty of uranium is left in the ground.

What are the advantages of nuclear power?

150

Stations are expensive to build and maintain. Takes longer to start up nuclear power stations than fossil. Processing uranium causes pollution. Leaks are a risk. Disposing of radioactive waste. Decommissioning is expensive. Uranium is non-renewable.

What are the disadvantages of nuclear power?

151

Full protective suits prevent radioactive particles being inhaled, lodging on skin/under fingernails. Lead-lined suits or barriers and thick lead screens shield workers from gamma in highly radioactive areas. Remote controlled robotic arms used.

What safety rules are there for working with radiation?

152

Like paper, gloves, clothing, syringes can be disposed of by burying it in a secure landfill

How can low level radioactive waste be disposed of?

153

Often sealed into glass blocks, then in metall canisters and then buried deep underground. Stays highly radioactive for tens of thousands of years.

How can low level radioactive waste be disposed of?

154

Gravitational attraction - pulls everything in Universe towards everything else.

What force is acting on everything in the solar system?

155

Circular motion is always caused by a force towards the centre of the circle. For planets, moon etc in an orbit, this force is gravity. A force that causes a circular motion is called a centripetal force.

What is circular motion and centripetal force?

156

When the Solar System was forming, rocks betweeen Mars and Jupiter didn't form a planet due to Jupiter's gravity interfering . This left millions of asteroids - rubble and rock - measuring up to 1000km in diameter.

How was the asteroid belt formed?

157

Rocks or dust that enters the Earth's atmosphere an burn up - so we see shooting stars. If it doesn't burn up, and hits Earth, they are meteorites.

What are meteors?

158

Fires can start, hot rocks and dust thrown in air, craters. Dust and smoke can block out sunlight causing climate change (species extinct).

What can happen if a meteorite hits Earth?

159

Layers of unusual elements in rocks and sudden changes in fossil numbers between adjacent layers of rock, as species suffer extinction.

How can we tell that asteroids have collided with Earth in the past?

160

Balls of rock, dust and ice orbit in elongated ellipses. Approaching sun, ice melts and creates tail of gas and debris. Speed up as they approach sun because Sun's graviational pull increases as it gets closer.

How do comets orbit?

161

Near-Earth Objects - asteroids or comets which might be on a collision course with the Earth.

What are NEOs?

162

Astronomers use powerful telescopes and satellites to search and monitor. When found, they can calculate the objects trajectory. Can be difficult to spot - they are small, dark and many have unusual orbits.

How are NEOs monitored?

163

Small NEOs would burn up harmlessly. Enough warning - may be able to deflect it. Eploding a bomb in, on or close to it might nudge it off course.

What happens if an NEO is heading for Earth?

164

When our planet collided side-on with Earth. A Mars-sized planet. In the heat, dense iron cores merged to form Earth's core and less dense material ejected. This orbited Earth and came together to be the Moon.

How do scientists think our moon was formed?

165

The moon has a lower density than Earth and doesn't have a big iron core like Earth. Moon rocks contain few substances which evaporate at low temperatures - suggesting the Moon formed from hot material.

What evidence is there to support the theory of the moon's formation?

166

The distance that light travels through a vacuum in one year. It is a measure of DISTANCE!

What is a light year?

167

When a really big star explodes. Have very large mass, small volume and very high density. Not visible - even light can't escape gravitational pull.

What are black holes?

168

Using x-rays emitted by hot gases from other stars as they spiral into the black hole.

How can astronomers observe black holes?

169

Have to carry loads of food, water and O₂, have to shield people from radiation, low gravity causes muscle wastage and loss of bone tissue. Psychologically stressful - same people in a small space for ages.

What are the issues with manned spacecraft?

170

No need to carry food, water, oxygen. Withstand extreme conditions humans can't. More instruments fitted instead of people. Cheaper, less spent on safety. In a crash, no one gets hurt.

What are the advantages of unmanned space probes?

171

Probes can’t think for themselves. Spacecraft can't do maintenance or repairs whereeas people can.

What are the disadvantages of unmanned space probes?

172

From distant objects: data needs to be beamed using radio waves. From nearer objects: probes or people could collect samples and physically bring them back to Earth.

How is data from spacecraft sent back to earth?

173

That all distant galaxies are moving away from us very quickly - and it's all the same result whichever direction you look in.

What does measurement of red shift suggest?

174

More distant galaxies have greater red-shifts than nearer ones. This means more distant galaxies are moving away faster than nearer ones - the Universe is expanding.

What is the relationship between red shift and more distant galaxies?

175

Scientists can detect low frequency microwave radiation coming from all directions and parts of the Universe. It is strong evidence of the Big Bang. As the Universe expands and cools, the CBR cools and drops in frequency.

What is cosmic background radiation?

176

That the Earth and planets all orbited the Sun which is at the centre of the universe, in perfect circles. It is a heliocentric model (sun at centre).

What did the Copernican model state?

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Using telescope (new invention) saw stars in line near planet. Stars never moved, seemed to be carried along with planet (Jupiter). Suggested not stars, but moons. Showed not all was in orbit around Earth - Ptolemaic wrong.

What evidence did Galileo find to support Copernicus?

178

Venus had phases. Amount Venus lit by Sun changed over time. Ptolemaic theory meant changes would be small, Venus would always be infront of Sun, but Copernican: Venus could move in front & behind Sun, changes would be big - like Galileo saw.

What did Galileo notice about Venus?

179

That everything orbited Earth in perfect circles. Also known as geocentric model. Ancient Greeks accepted theory in the 1500s until Copernican model put forward.

What did the Ptolemaic model suggest?

180

Gravity makes the gas an dust used to form stars spiral together. Gravitational energy has been converted into heat energy so the temperature rises.

How is a protostar formed?

181

When temperature gets high enough, hydrogen nuclei undergo thermonuclear fusion - form helium nuclei & gives out heat & light. Star enters long stable period where heat created by fusion provides outward pressure to balance gravity pulling everything inwards. Typically lasts several billion years.

How is the main sequence star formed?

182

Hydrogen begins to run out and the star then swells in to a red giant - it becomes red because the surface cools.

How is a red giant formed?

183

A small-to-medium-sized star like the Sun then becomes unstable and ejects its outer layer of dust and gas as a planetary nebula.

How is a planetary nebula formed?

184

The planetary nebula leaves behind a hot, dense solid core - a white dwarf - which just cools down and eventually fades away.

What is a white dwarf?

185

Big stars form red supergiants - start to glow brightly again as they undergo more fusion & expand & contract several times, forming heavier elements in various nuclear reactions. Eventually they explode - supernova.

What leads to a supernova?

186

Exploding supernova throws outer layers of dust and gas into space, leaving very dense core called a neutron star. If star is big enough, becomes black hole.

How are neutron stars formed?

187

What are the disadvantages of fossil fuels?

  • Cause acid rain and carbon dioxide.
  • Bought from other countries = no control prices and supply.

188

  • Cause acid rain and carbon dioxide.
  • Bought from other countries = no control prices and supply.

What are the disadvantages of fossil fuels?