Physics, P2

Photocells use the Sun's light to produce electricity. Don't produce when dark. use renewable energy source, don't need fuel, no pollution. Sunlight conatins energy packets called photons. these cause free electrons to move producing an electric current.

Passive solar heating uses glass to help keep buildings warm. during day sun warms walls, floors. during night walls, floors radiate energy back into the room.

Ths Sun is a stable energy source. It transfers energy as light and heat to Earth.

Kinetic energy from moving air turns the blades on a wind turbine to produce electricity. don't work if no wind, or if wind speed is too great. Can be noisy, impact on countryside.

A dynamo produces electricity when coils of wire rotate inside a magnetic field. The size of the current depends on:

• The number of turns
• the strength of the field
• The speed of rotation

Transformers change the size of the voltage and current. The national grid transmits electricity around the country at high voltage and low current for the same power. this reduces energy loss, electricity prices an distribution costs

Nuclear fuels are radioactive. the radiation produced can cause cancer. Waste products remain radioactive for long time.

When two planets collide, a new planet and a moon may be formed.

The earth is surrounded by a magnetic field similar in shape to that bar magnet or coil of wire.

The core of the earth contains molten iron.

Solar flares are the result of clouds of charged particles being emitted from the sun at high speed disturbing the magnetic field around Earth.

Cosmic rays- stream of charged particles originating the Sun and other bodies in space. they travel very quickly, have a lot of energy, interact with earths magnetic field as they spiral around field lines concentrating at the poles, cause the auroras.

Light-years- distance light travels in one year.

Comets- speed increases as it approaches the Sun and vice v. result of gravitational forces. orbit of comet very elliptical. viable from earth at times as suns heat vapourises material from their surface, forming a tail of debris

Universe is explored by telescopes on Earth and in space. Large distances mean that it takes a long time for information to be received and inter-galactic travel is unlikely.

Scientists believe the universe started from the big bang.

Almost all galaxies in the universe are moving away from each other. The furthest galaxies are moving fastest. The universe is expanding all the time.

More distant source of light- more red shift

Most asteroids between Mars and Jupiter, some pass closer to Earth.Jupiter has a very large gravitational field strength. Its gravity stops rocks from coming together to form a planet. Instead, they orbit the Sun as asteroids.

They are constantly being monitored. An asteroid strike could cause climate change and species extinction

Planets, asteroids and comets orbit the sun in our solar system. the universe consists of many galaxies. Centripetal forces keep bodies in orbit.

The main forms of ionising radiation are:

• Alpha- used in smoke alarms- weakest
• Beta- used in rolling mills to control thickness
• Gamma- injected into the body as tracers, used in rolling mills to control thickness- strongest

Their uses depend on their penetrative and ionisation properties.

Ionisation involves gaining or losing electrons:

• When the atom gains electrons, it becomes negatively charged
• When the atom loses electrons, it becomes positively charged

some radioactive waste can be reprocessed into new, useful radioactive material. Radioactive waste must be stored safely, as it can remain radioactive for 1000s of years. It must be stored where it can't leak into natural underground water supplies and then into lakes and rivers.

Advantages

• Fossil fuel reserves aren't being used
• there's no atmospheric pollution
• No carbon dioxide is produced so no global warming effects

Disadvantages

• nuclear power stations have high maintenance costs, decommissioning costs and produce quantities of radioactive waste
• there's a risk of a major accident similar to one at Chernobyl

Medium-sized (like Sun)- becomes red giant, core contracts,outer part expands and cools, changes colour yellow- red during this phase, gas shells (Planetary nebula) are thrown out,the core becomes a white dwarf (shining very brightly), eventually cools to become a black dwarf

Large stars- become red supergiants as core contracts and the outer part expands. the core suddenly collapses to form a neutron star, then an explosion (supernova), remnants from a supernova can merge to form a new star. the dense core of the neutron star continues to collapse until it becomes so dense it forms a black hole

stars have a finite life depending on their size. small stars shine longer have less hydrogen use it up at a slower rate.

swirling cloud of dust and gas- nebula. Nebula clouds are pulled together by gravity into a spinning ball of gas, which starts to get hot and glow.

Protostar- is shining but can't be seen as of the dust cloud. gravity causes the star to become smaller, hotter and brighter.

nuclear fusion- after millions of years, the core temp is hot enough. As hydrogen nuclei join together to form helium nuclei. energy is released. the star continues to shinewhile there's enough hydrogen.

power=voltage x current

energy used= power x time

cost of electricity used= energy used x cost per KWh

fuel energy input= waste energy output + electrical energy output

frequency (in hertz) = 1 / period (in seconds)

efficiency= useful energy output / total energy input

energy= mass x specific latent heat

energy = mass x specific heat capacity x temp change