Physics P2

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What are the advantages of photocells?
They do not need much maintenance, they don't need fuel, and they cause no pollution
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What is the only disadvantage of photocells?
They don't produce electricity when it is dark or cloudy
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What is a photocell made of?
It is made of two pieces of silicon to make a P-N junction, one has an impurity that produces an excess of free electrons, and the other has an impurity that produces a lack of free electrons.
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How does the photocell work?
The sunlight produces photons that cause the free electrons to move, creating an electric current.
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What does the output of a photocell depend on?
The light intensity, how close the light source is, and the surface area exposed to light
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How does passive solar heating work?
The walls and floors inside absorb the infrared radiation from the sun, warm up and re-emit it back out
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How can the current from a dynamo be increased?
Rotating the magnet faster, increasing the number of coils, and making the magnet stronger
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Where can the output of a dynamo be displayed?
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How does a simple generator work?
The coil cuts through the electromagnetic field, which produces a current in the coil.
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How do power stations function?
The water boils to produce steam, which turns the turbine, which drives a generator
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Which wavelength cannot pass through the earths atmosphere?
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Where does carbon dioxide occur naturally?
Forest fires, eruptions, decay of dead matter, from oceans and respiration
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How is man-made carbon dioxide caused?
Burning fossil fuels, deforestation and the manafacture of cement.
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What is the most significant greenhouse gas?
Water vapour
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How is methane produced?
When an organic matter decomposes in a lack of oxygen
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How can dust raise the temperature of the atmosphere?
Dust from factories can reflect radiation.
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How can dust lower the temperature of the atmosphere?
ash clouds reflect radiation from the sun.
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What does the choice of energy source depend on?
Availability, effect on the enviroment, any risks and ease of extraction
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What do the national grid use to transport electricity?
Step up and step down transformers
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What do the step up transformers do, and how is it helpful?
They increase the voltage, and it reduces energy loss, reduces costs, and makes the electricity cheaper for consumers.
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What happens to the current when the voltage is increased?
The current decreases
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What makes atoms neutral?
They contain the same number of protons and electrons
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What does ionisation involve?
The gaining or losing of electrons
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What happens when atoms gain/lose electrons?
They become negative/positive
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What three types of radiation come from the nucleus?
Alpha, beta, and gamma
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Which radiation caues the most ionisation?
Alpha radiation
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How can alpha radiation be stopped?
By a sheet of paper
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How can beta radiation be stopped?
by a few millimeters of aluminium
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How can gamma be stopped?
It can't, but is can be mostly by a few centimeters of led
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What do smoke alarms contain?
Alpha radiation
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Why is gamma used for sterilising?
Because it kills bacteria and microbes
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What is plutonium in terms of waste?
It is waste from nucelar reactors
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How can some low level radioactive waste be dealt with?
By burying it in landfill sites
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What are the advantages of nuclear power stations?
Fossil fuels are not used and no greenhouse gases are released into the atmosphere
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What are the disadvantages of nuclear power stations?
High maintenance and high costs
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What type of orbits do comets have?
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What is a meteor made of?
grains of dust that burn up as they pass through the atmosphere
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Where a black holes formed?
Where stars used to be
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Why can't you see a black hole?
because light cannot escape from it, and they are very small
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Why do moons orbit planets?
Because of the centripetal force.
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Why are unmanned probes better?
They can go to places where humans can't
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How is the gravity different in space?
The gravity is much less than on earth
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Why are unmanned spacecrafts better?
Because they don't put lives at risk
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How long does light take to reach earth from the sun?
about 8 minutes
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What are asteroids?
mini-planets orbiting the sun
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How were all asteroids and planets formed?
when clouds of gas and dust collapsed together due to the gravitational forces
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What determines an objects gravitational force?
Its mass
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What do scienctists believe about the origin of our moon?
It was the result of a collision between two planets in the same orbit. The core melted and formed with rocks from earth, and melded to form our moon
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What evidence do geologists have for claiming that asteroids have collieded wih earth?
Near craters metals were found which do not associate with earth, but are common in meteorites
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Which way does the tail of a comet point?
Always away from the sun
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What is happening to the galaxies?
They are moving further away from eachother
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Why did catholics not support galileo's model of the universe?
because they believed that the earth was the centre of the universe
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What is red shift?
When a source of light moves further away, increasing wavelength which shifts light towards the red end of the spectrum.
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What is a nebula?
A swirling cloud of gas and dust
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How are stars formed?
Nebula clouds are pulled together by gravity, causing the star to become smaller, hotter and brighter after milions of years. Nuclear fusion takes place and the star continues to shine only whilst it has enough hydrogen
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What happens when a star's life ends? (Medium stars)
A medium star becomes a red giant. while the outer cols, the inside contracts, and it changes colour from yellow to red and expands. Gas shells are thrown out and the core becomes a white dwarf, but eventually cooling to a black dwarf.
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What happens when a star's life ends? (Large stars)
Large stars become red supergiants, the core contracts and the outer part expands. The core colapses to produce a neutron star and an explosion called a supernova. Remnants form to create a new star, the core collapses and becomes a black hole.
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Why do black holes have such a strong gravitational pull?
Because it has a small volume, but a huge mass and density.
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What form of energy is wind?
It is a renewable form of energy
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Why does the effectivness of a wind turbine depend on the weather?
Because it can not function if it is too windy, or if there is not enough wind
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What are the advantages of wind turbines?
They do not contribute to global warming, and they don't pollute the atmosphere
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What are the disadvantages of wind turbines?
They can be noisy, and can spoil viewsand landscapes
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What does an oscilloscope trace show?
How the current produced by the dynamo varies with time
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What is the period of the alternating current?
The time for one complete cycle
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What is efficiency a measure of?
how well a device transfers energy
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Wher is energy lost in a power station?
Boilers, generators and cooling towers
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What radiation from the sun has a relatively short wavelength?
electromagnetic radiation
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What is this radiation absorbed by?
The earth
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What effect does this have on the earth?
It warms it
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What is longer wave radiation absorbed by?
by greenhouse gases which also warms the earth
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What should decisions about global warming be based on?
Scientific data
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What do scienctists agree on in terms of global warming?
That the average temperature has increased
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What do some scienctists disagree on?
The extent to which human activity has contributed to it
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Why do we have to pay less for electricity at night?
Because we don't need it as much, but it is still being produced
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What happens to the temerature of the wire as the current passes through it?
The temperature of the wire increases
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The greater the current...?
The hotter the wire
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How does an atom become negatively charged?
by the atom gaining electron(s)
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How does an atom become positively charged?
by the atom losing electron(s)
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What can the formation of ions cause?
Chemical reactions
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What radiation causes the least ionisation?
gamma radiation
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How do smoke alarms work?
the radiation ionises the oxygen and nitrogen ions in the air which causes a small electric current that is detected. When smoke fills the air, the air wont be ionised as much so the current is less and the alarm sounds
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How can thickness of paper be monitered?
by using a source of beta radiation and a detector.
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How does it work?
the amount of radiation passing through the paper is monitered and the pressure of the rollers is adjusted accordingly
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How is high level waste disposed of?
It is encased in glass and buried deep underground or is reprocessed
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Why do meteors look as if they have tails, also known as shooting stars?
Because they heat the air around them which glows
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How is the visor adapted on a spacesuit?
It is dark so stops the astronaut from being blinded
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How is the spacesuit adapted?
It is pressurised and has an oxygen supply
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Why do unmanned spacecrafts have to be reliable?
Because there is usually no way of repairing them when they break.
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Where do most asteroids orbit?
between mars and jupiter
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What scienctific evedience is there to support scienctists theory about our moon being created by a collision?
The average density of the moon is lower than that of the earth, There is no ron in the moon, it has the same oxygen composition as the earth
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What happens to the speed of a comet as it orbits the sun?
It increases as it approaches the sun, and decreases as it moves away from the sun.
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Why does this happen?
Because of the changing gravitational attraction
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What did Galileo observe?
Four moons orbiting jupiter
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What did this solidify?
The theory that not everything orbits earth, and that planets orbit the sun
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What can sienctists work out using information about red shifts?
The age of the universe
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Why do small stars shine for longer than bigger stars?
Because they have less hydrogen, but use it up slower
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Other cards in this set

Card 2


What is the only disadvantage of photocells?


They don't produce electricity when it is dark or cloudy

Card 3


What is a photocell made of?


Preview of the front of card 3

Card 4


How does the photocell work?


Preview of the front of card 4

Card 5


What does the output of a photocell depend on?


Preview of the front of card 5
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