P2 Radiation and LifeREVISION NOTES BASED ON COLLINS NEW

GCSE SCIENCE AND ADDITIONAL SCIENCE

Sig’s School Work Help

Electromagnetic Spectrum

T.V & Radio waves

Microwaves Infrared

VISABLE

Ultra Violet X-Ray Gamma

Increasing wavelength

Energy increases&

Frequency increases ALL:

• Travel at speed of light in a

vacuum

• Emit Electromagnetic Radiation

If you want, find some examples of

items that use these types of

radiation

Intensity

Energy per second

XIntensity Area

Intensity = Energy per Second Add these units to your answer: J/S/M² or W/M²Area

(that photons are falling on)

Joules per Second per Metre squared

Watts per Metre squared

The intensity of a beam of radiation depends on:• The energy of the photons – the type of radiation• The number of photons per second• The area with which the photons are colliding

Ionisation

Ultra violet, X-rays and Gamma radiation can create ions because they have so much energy• If ions are created in our cells, this can cause them to reproduce abnormally

and they may form a tumour• If the tumour is cancerous it can be very dangerous• Although some gamma radiation can cause cancer, in high doses it can be

used to kill/exterminate cancer cells

Energy Diagrams - Scientific

• P= Current x

Voltage

Or

• P= Energy

time

• Unit= kw x h

• Units for

Power= Watts

of J/S

Power is the rate at which energy is convertedPower = Energy

TimeEnergy (J)

XPower (W or J/S) Time (S)

Electrical Power = Current x Voltage

Power (J/S or W)

XCurrent (A) Voltage (V)

Energy Diagrams –Calculating Energy

• P= Current x

Voltage

Or

• P= Energy

time

• Unit= kw x h

• Units for

Power= Watts

of J/S

Energy (J)

XPower

(kW)

Time

(Hour)

Energy = Power x Time = kilowatts x Hours

So when paying for electricity we calculate the power in kilowatts and the time in hours

1 kW = 1000 W

E.g. A 5000W motor running for 3 hours uses:

5 kW x 3 Hours = 15 units/hor

15 kW/h

Sankey Diagrams

A Sankey Diagram shows how energy is converted to different types in a system. We always assume that energy is conserved (the total energy input is the same as the energy output).

1000J

300J

150J 50J

500J

Microwaves

How they work:The oven generates microwaves, which are directed at the food. Water molecules in the food absorb the photons. This causes the molecules to vibrate and they pass on their vibrations to other water molecules. In this way heat is conducted throughout the food.

In order to protect us from microwave radiation, the ovens have metal casing to reflect the photons back into the oven and a metal mesh in the glass part of the door, which also reflects the radiation.

Mobile Phones:Mobile phone networks use low intensity microwaves. The heating effect of these microwaves is very small but some people are concerned about the health risks from the radiation; the risk of cell damage from mobile phones is measured by comparing cancer rates in large groups of people who do and do not use mobile phones.

There is no evidence of

harm from mobile

phone use

Ozone• Ozone is a form of oxygen found in the outer layers of our atmosphere, which absorbs ultraviolet rays from the

sun (only radiation absorbed by ozone)

• Ultraviolet radiation causes sunburn and can lead to skin cancer and eye damage to the retina

• Chemicals containing CFC’s (Chlorofluorocarbons) were invented with many uses including refrigeration, aero-sols and fire-fighting; about 50 years ago, researchers realised that these chemicals /CFC’s were damaging the ozone layer due to the break down of the ozone molecule

• When a photon of ultraviolet radiation meets an ozone molecule, all its energy is absorbed in splitting the molecule. The molecule then reforms to absorb the next photon. This is how the ozone layer protects us

OO O

Ozone is O³

• The sun emits different frequencies of electromagnetic radiation. This radiation reaches the Earth’s atmosphere

• The Earth’s atmosphere reflects some of this radiation back to space

• The Earth’s atmosphere transmits some of this radiation to the Earth’s surface

• The Earth’s surface absorbs radiation that reaches it, and it warms up. Because the Earth’s surface is warmer it emits more electromagnetic radiation

• The Earth’s atmosphere reflects some radiation back to the Earth’s surface

• The Earth’s atmosphere absorbs some radiation and re-radiates it back to earth

• The Earth’s atmosphere transmits some radiation back to space

• The Earth and its atmosphere become warmer if more radiation is absorbed than emitted

Greenhouse Effect

The main greenhouse gases are • Methane• Carbon dioxide• Water vapour

The principle frequency of that radiation is the one with greatest intensity; increases with increasing temperatureRadiation from the hot Sun has a higher frequency than radiation from the cool earth

Global Warming• The greenhouse effect is slowly increasing the average temperature worldwide. This is called global

warming

• Global warming will have many effects including:• Changes to the crops which can grow in a region• Flooding of low-lying land due to rises of sea level as the sea expands and glaciers melt

• Various gases in the atmosphere are responsible for the greenhouse effect:• Water vapour has the most effect, because there is so much of it• The small amount of carbon dioxide has an affect• Methane is a strong absorber of infrared radiation; there is very little of it

• Scientists use computer models to predict the effects of global warming. The models are tested by seeing if they can use past data to predict today’s climate

• Models suggest that global warming will result in more extreme weather events because of:• Increased water vapour in the hotter atmosphere• Increased convection in the atmosphere increasing wind speed

• Carbon Dioxide is one of the main greenhouse gases found in the Earth’s atmosphere

• The level of Carbon Dioxide in the atmosphere has been steady for thousands of years, because the rates of absorption and release of Carbon Dioxide have been the same

• But, in the last 200 years the levels have steadily increased due to:

• The burning of fossil fuels as an energy source has increased the rate of release

• Cutting down forests (deforestation) to clear land has decreased the rate of absorption

• The recent increase in the temperature of the Earth correlates with the rise in Carbon Dioxide levels in the Earth’s atmosphere. Many scientists believe that this correlation is caused by the Carbon Dioxide because it is a greenhouse gas

CO² in the atmosphere

Electromagnetic Waves For Communication

Waves that carry information:• Conversations, music, pictures and other

information can be carried from place to place using electromagnetic waves

• The main types of radiation used for communication are radio wave, infrared radiation and visible light Microwaves can

pass through the atmosphere to satellites but longer wavelength radio waves are reflected

Radio Waves Microwaves InfraredTransmit terrestrial T.V. and radio programmes from a transmitter to a receiver; the waves are not strongly absorbed by air so they can travel many kilometres and are able to spread around hills, buildings but also reflect off layers in the atmosphere

Have a shorter wavelength than radiowaves and are slightly absorbed by the air.Narrow beams of microwaves travel many kilometres through the atmosphere and interact with satellites

Used (in remotes) as it can only travel short distances in air and cannot pass through walls, this means that the remote will not be controlling another/different T.V.

Optical fibres

• Very narrow glass fibres called optical fibres carry infrared and light signals long distances

• Infrared radiation and visible light are not absorbed much in glass, repeatedly reflecting off the sides of the glass fibre

• Optical fibres are used in telephone, internet and T.V. cables

• More than one signal can pass through an optical fibre at the same time

You tune your radio to a certain frequency to listen to your favourite radio station; This frequency is the frequency of the carrier wave. A carrier wave is a radio wave which carries information from the broadcasting station to your radio

No programme is broadcast

Information containing the programmes sounds or images is added to the carrier wave. The carrier wave is modulated

This creates a signal that is transmitted to your radio set

Your radio can separate out the modulation from the carrier, so you can hear the programme

In analogue broadcasting, the signal added to the carrier wave can vary continuously. This is an analogue signal. The frequency of the carrier wave and its amplitude can have any value

How Waves Carry The Information

Carrier Wave

Sound Signal

Carrier wave modulated by sound signal

Noise is an unwanted signal mixed in with the signal we want. Since digital signals consist of a series of steps, it is easier to separate noise from a digital signal than from an analogue signal. Also, when an analogue signal is amplified, the noise gets amplified as well

Digital VS Analogue Signals

A digital signal is made of a series of discrete (separate) steps. For example: a normal light

switch, a digital thermometer; has a number of ‘0’ or ‘1’ values

An analogue signal is continuous. For example: A dimmer switch, a liquid-in-glass thermometer

Storing Digital Information:• Bit – a binary digit i.e. a ‘O’ or ‘1’• Byte – 8 bits• Kilobytes – 1000 bytes• Megabytes – 1,000,000 bytes• Gigabyte – 1,000,000,000 bytes• Pixel – An area of an image. The

smaller the pixels the clearer the image