Physics OCR GCSE P2 (higher)

How photocells work...

It absorbs the suns energy and this causes electrons to be knocked loose from the silicon crystal. These electrons can now flow freely within the silicon. this flow is called an electric current.

To maximise the power output and efficient solar collector must track where the sun is in the sky but this requires extra technology and therefore more money.

Wind turbines

Wind turbines are another way of collecting energy without burning fossil fuels. They transfer the kinetic energy from the wind into electrical energy.

Harnessing the sun's energy

Light can be absorbed by a surface and transferred into heat energy. Water passed over this surface will then me heated and can be used for heating buildings.

1. What is a photocell?

a flat silicon panel that can collect light energy and transfer it into heat energy. 

2. List five main advantages of a photocell:

• Requires little maintenance once installed
• Can operate in remote locations to give access to electricity without power cables
• Have a long life
• Need no fuel because use sun which is renewable 
• No pollution.

3. Give three disadvantages of wind turbines

• Require a large amount of space
• dependant on the wind
• cause visual pollution because they are very big

Electricity can be generated by moving a wire or a coil of wire near a magnet or vice versa. this creates a current. The current can be increased by...

• Using stronger magnets
• Using more turns in the coil
• Moving the coil or magnet faster.

How an AC Generator works...

In an AC Generator a coil of wire is rotated in a magnetic field. As the coil cuts through the magnetic Field a current is generated in the coil.The current alternated, i/e It reverses its direction of flow every half turn of coil.

Producing electricity

the heat energy for our power stations comes from burning fuels. when the fuel is burned it releases heat energy which boils water to produce steam. the steam then drives the turbines and ultimately the generations which produce electricity.

1. Explain why we use transforms:

Because when there is a large current running through a power line the cable will soon become hot and alot of the energy is lost to heat energy. If it has be transformed to a height voltage to reduce the current and therefore a smaller  amount of energy is lost through heat.

2. A power station uses 200000J of fuel energy to produce 80000J of electrical energy. What is the the efficiency of this power station?

Efficiency = Electrical energy output / Fuel energy input    x100% 

                = 80000/200000 x 100%

                = 0.4 x 100%

                = 40%

The type of fuel we use depends upon the economical and environmental costs. Common fuels used are...

• Fossil fuels (crude oil, coal and natural gas)
• renewable biomass (wood, straw, and manure)
• Nuclear fuel (uranium fuel rods release energy as heat)

Kilowatt-hours

the number of kWh depends of these two things :

• the power of the appliance (kW)
• the time the appliance is left on (h)

to calculate the total cost we use this formula:

TOTAL COST = NUMBER OF KILOWATT-HOURS (kWh) x TIME (h)

1. Name two disadvantages of using nuclear power:

• the radioactive waste can be harmful to humans.
• It is non renewable 

2. How do you work out Power (watts)?

POWER (Watts)= CURRENT (Amps)  x VOLTAGE (Volts)

3. What is the equation for working out total number of Kilowatt-hours (kWh)

NUMBER OF KILOWATT-HOURS (kWh) = POWER (kW) x TIME (h)

4. An air conditioning unit is supplied with 2.5kW of electrical energy over a two hours period. Work out the power rating:

2.5 (kW) x 2 (h) = 5 (kWh)

Types of radiation

Radioactive materials are substances that give out nuclear radiation all the time no matter what is done to them. They give out one of these three types of nuclear radiation:

• Alpha (hydrogen nucleus consisting of two protons and two neutrons)
• Beta (fast moving electron)
• Gamma (very high frequency electromagnetic radiation)

Background radiation happens all the time but it is not harmful to us because it is only in small amounts from the earth and cosmic rays from the sun. However when it becomes stronger the danger increases. Because of this when scientist hold radioactive materials they must wear protective clothing, keep their distance and try to minimise exposure time.

1. Give two reasons radioactive substances should be carefully disposed of.

• they could be used by terrorist groups to infect water and kill thousands of people.
• they could still produce a small amount or radiation so shouldn't be disposed near schools or hospitals.

Give a use of each type of radiation:

Alpha - smoke detectors, smoke stops the radioactive substance from producing alpha particles this means that when the circuit stops the alarm goes off.

Gamma - to treat cancer

Beta - Measuring the thickness of paper when the gamma particles are detected the other side of the aluminium it is too thin.

The earths magnetic field

The earth has a magnetic field around it which is just like a magnet, me have a north magnetic pole and a south magnetic pole. It is believed that the cause of this magnetic field is the large amounts of molten iron in the earths core.

Magnetic field around a coil

When electric current (moving electrically charged particles) is passed through a coil a magnetic field is created.

It looks very similar to the current around a bar magnet and also earths current is also similar.  

The earth moon system

The magnetic field produced by the earth may be the result of a gigantic collision in the past. The theory is that two planets collided and the iron cores or each planet merged to form earth and the less dense material is the moon.

1. What are solar flares?

they are clouds of charged particles that are ejected at high speeds from the sun.

2.What are cosmic rays?

fast moving particles that create gamma rays when they hi our atmosphere.

3. how can solar flares effect our planet?

they can inter fear with satellites that we use for

• telecommunications
• Forecasting weather
• Spying
• Navigation systems

The universe 

• Stars (our sun is a star they can be seen clearly seen even through they are far away because they are very hot and give out light.
• Planets, comets and meteors
• galaxies (large groups of stars)
• Black holes (dense dying stars with strong gravitational pull) 

Moons comets and meteors

Comets have a core of frozen gas and dust and they have an elliptical orbit around the sun. They can be up to 20km in diameter. As they approach the sun, the gases evaporate to form the tail. this is what we can see in the night sky.

meteors or shooting stars are fragments of dust and rock. they are much smaller than comets. As they enter earths atmosphere they burn up due to friction and give out light, this makes them easy to see.

1. Imagine you are an engineer building a rocket for a manned space mission to Pluto. What difficulties would you have to take into account?

Oxygen supply. Food and drink supply. It would also take a long time because of the distance to I would have to think about how to make the space craft to support this time with enough fuel. I would also have to include exercise for the astronaut's. I would also have to find a way to maintain the temperature in the spacecraft.

2. Why might an unmanned spacecraft be a better idea?

an unmanned spacecraft would be better because they wouldn't have to carry the food oxygen and water for the humans so this would make the space craft weigh less and therefore not have to use as much food. we would also not have to worry about temperature.

3. What is a light year and what do we use them for?

The distance light travels in one year. we use this for measuring very long distances.

Asteroids

asteroids are rocks left over from the formation of the solar system. They normally orbit the sun in the asteroid belt between mars an Jupiter, but occasionally they get knocked off course and head towards earth.

When an asteroid collides with earth there can be several consequences

• the impact would form a crater, which could trigger the ejection of hot rocks.
• the heat may cause widespread fires.
• Sunlight could be blocked out by the dust from the explosion.
• Could cause Climate change
• whole species could become extinct and this could effect the food chains

1. What is a NEO and what does it stand for

Near earth object, a comet or asteroid that is on a collision path with earth. They might have a devastating effect on life on earth but there are things we can do to prevent this.

2. what can we do to prevent NEO hitting earth?

• Survey the skies with telescopes to identify NEOs as early as possible.
• Monitor the progress with satellites
• Deflect the object with an explosion if a collision does seem likely.

The big bang

The theory scientists use to explain life on earth and the start of the universe is called The Big Bang Theory. This theory states that the whole universe is slowly expanding and that it all started billions of years ago in one place with a huge explosion, the big bang.

Red shift

We can tell how far away they are and if galaxies are moving towards or away from us using a thing called Red shift. If the source or light was moving away from us, the wavelengths of the light in its spectrum are longer than if the source was not moving. this is known as the red shift because wavelengths are shifted toward the red end of the spectrum.  

1. give one way scientists can prove the big bang:

detection of microwaves which were a by-product of the big bang.

2. show the two possible life stages of a star:

Star - Red super giant - supernova - black hole or neutron star

star - red giant - planetary nebula - white dwarf

3. what is the difference between a neutron star and a black hole?

A black hole cannot be seen because it is black and so is space. Black holes also **** in any matter close together with its massive gravitational pull.