physics

> energy transferred (kilowatt-hours, kWh) = power of device (kilowatts, kW) X time in use (hours, h)

> total cost = number of kWh used X cost per kWh

using electrical energy

> the national grid is a network of cables and transformers

> we use step-up transformers to step up the power stations' voltages to the grid voltage

> we use step-down transformers to step the grid voltage down for use in our homes

> a high grid voltage reduces energy loss and makes the system more efficient

the national grid

> electricity generators in power stations are driven by turbines

> much more energy is released per kilogram from uranium then from fossil fuels

fuel for electricity

> a wind turbine is an electricty generator on top of a tall tower

> a wave generator is a floating generator turned by the waves

> hydroelectricty generators are turned by water running downhill

> a tidal power station traps each high tide and uses it to turn generators.

energy from wind and water

> we can convert solar energy into electricty using solar cells or use it to heat water directly in solar heating panels

> geothermal energy comes from the energy released by radioactive substances deep inside the earth

power from the sun and the earth

> fossil fuels produce greenhouse gases

> nuclear fuels produce radiactive waste

> renewable energy resources can affect plant and animal life

energy and the environment

> the electromagnetic soectrum ( in order of increasing wavelength) is:

• gamma rays and x rays
• ultraviolet
• violet
• indigo
• blue
• green
• yellow
• orange
• red
• infra red
• microwaves
• radio waves

> all electromagnetic waves travel through space at a speed of 300 million m/s

>wave speed= wavelength X frequency

the electromagnetic spectrum

> x-rays and gamma radiation are absorbed by dense materials such as bone and metal

> x-rays and gamma radiation damage living tissue when they pass through it

> x-rays ar used in hospitals to take radiographs

> gamma rays are used to kill harmful bacteria in food, to sterilise surgical equipment and to kill caner cells

gamma rays and x-rays

> ultraviolet radiation is in the electromagnetic spectrum between violet light and x-radiation

> ultraviolet radiation has a shorter wavelength than light

> ultraviolet radiation harms the skin and the eyes

light and ultraviolet radiation

> the use we make of radio waves depends on the frequency of the waves

> visible light and infra red radiation are sued to carry signals in optical fibres

communications

> analogue signals vary continuously in amplitude

> digital signals are either high ('1') or low ('0')

> digital transmission, when compared with analogue transmission, is free of noise and distoration. It can also carry much more information

analogue and digital signals

> a radioactive substance contains unstable nuclei

> an unstable nucleus becomes stable by emitting radiation

> there are 3 types of radiation from radioactive substances

• alpha radiation
• beta radiation
• gamma radiation

> radioactive decay is a random event- we cannot predict or influence when it will happen

observing nuclear radiation

> alpha radiation is stopped by paper or a few centimetres of air

> beta radiation is stopped by thin metal or about a metre of air

> gamma radiation is stopped by thick lead and has an unlimited range of air

alpha, beta and gamma radiation

> the half-lite of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve

> the number of unstable atoms and the activity decreases to half in one half-lite

half-lite

> the use we can make of a radioactive substance depends on

• its half-lite
• the type of radiation it gives out

radioactivity at work

> light from a distant galaxy is red-shifted to longer wavelengths

> the most distant galaxies are about 13,000 million light years away

> the universe is expanding

the expanding univers

> the universe started with the Big Bang, a massive explosion from a very small point

> background microwave radiation is radiation created just after the big bang

the big bang

> the earth's atmosphere absorbs all eceltromagnetic waves (except visible light, radio waves and some ultraviolet radiation)

> satellite detectors are used to make observations outside the visible and the radio spectrum

> we also get clearer images from telescopes on satellites detecting visible light

looking into space