Physics Topic 2 Revision

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  • Created by: faithper
  • Created on: 18-03-18 18:29

Wave Basics

 Waves - Waves travel through a medium, and when the particles of the medium vibrate and transfer energy. Overall, the particles stay in the same place. 

Wave Diagrams -

Amplitude - Is the displacement of the wave from the rest position to a crest or trough. (The crest is above the rest position and the trough is below). 

Wavelength - Is the length of a full cycle of the wave from crest to crest or compression to compression) 

Frequency - Is the number of complete cycles of the wave passing a certain point per second. Frequency is measured in Hertz (Hz) 

Period - The period of the wave is the number of seconds it takes for one full cycle (To find this use Period = 1 / frequency 

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Wave Basics

Transverse Waves - 

1) The vibrations are perpendicular to the direction of travel 

2) The vibrations go up and down from the resting position. 

Waves such as electromagnetic waves and S-waves are transverse waves. 

Longitudinal Waves -

1) The vibrations travel parallel to the direction the wave travels. 

2) Vibrations are compressed (High pressure, lots of particles) and rarefacted (Low pressure, fewer particles). 

Wave speed = Wavelength x Frequency 

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Measuring Waves

Oscilloscope -

By attaching a signal generator to a speaker you can generate sounds with a specific frequency. Use two microphones and an oscillioscope to find the wavelength of the sound waves generated. 

1) Set up the oscillioscope so the detected waves at each microphone are shown as seperate waves. 

2) Start with both microphones next to the speaker, then slowly move one away from the other until the two waves are aligned on the display but have moved exactly one wavelength apart. 

3) Measure the distance between the microphones to find one wavelength. Use v= frequency x Wavelength to find the speed (V) 

The frequency is whatever the signal generator is set to in the beginning of the experiment. 

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Measuring Waves

Measure the speed of water ripples using a strobe light -

1) Using a signal generator attached to a dipper of a ripple tank, create water waves at a set frequency. 

2) Dim the lights and turn on the strobe light - you should see a wave pattern made by the shadows of teh wave crests on the screen below the tank. 

3) Alter the frequency of the strobe light until the wave pattern on the screen appears to have frozen. This happens because the frequency of the waves and the strobe light are equal, so the waves appear to not move because they are being lit at the same point in their cycle everytime. 

4) The difference between each shadow line is equal to one wavelength. Measure the distance between the lines that are 10 wavelengths apart and then find the average wavelength. 

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Measuring Waves

Measuring Wave Speed in Solids -

This can be done by measuring the frequency of the sound waves produced when you hit an object. 

1) Measure and record the length of a metal rod. 

2) Use a clamp to hold elastic bands. The elastic bands are used to dangle the metal rod. Using a hammer on one end, hit the elastic bands, and the microphone on the other end of the metal rod which is connected to a computer. 

3) Using the information from the computer, write down the peak frequency, and repeat this process 3 times to find an average peak frequency. 

Use the equation wave speed = frequency x wavelength. The wavelength in this practical is twice the length of the rod. 

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Measuring Waves

Measuring Wave Speed in Solids -

This can be done by measuring the frequency of the sound waves produced when you hit an object. 

1) Measure and record the length of a metal rod. 

2) Use a clamp to hold elastic bands. The elastic bands are used to dangle the metal rod. Using a hammer on one end, hit the elastic bands, and the microphone on the other end of the metal rod which is connected to a computer. 

3) Using the information from the computer, write down the peak frequency, and repeat this process 3 times to find an average peak frequency. 

Use the equation wave speed = frequency x wavelength. The wavelength in this practical is twice the length of the rod. 

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Wave Behaviour at Boundaries

Waves can be: 

Absorbed - Waves can be absorbed by another material, as the wave transfers energy to the second materials energy stores. Commonly, the energy is transferred to the thermal energy store, causing heating. 

Transmitted - The waves carry on travelling through the second material, often leading to refraction. This is used in communication and also in the use of lenses. 

Reflected - This is where the incoming ray is 'sent back' in the same angle as it was received by the material. 

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Refraction

Practical - Ray Diagrams 

1) Draw the boundary between the two materials. 

2) Draw the incoming incident ray that meets the normal of the boundary. (This is at a 90 degree angle, so perpendicular to the boundary). 

3) The angle between the ray and the normal is the angle of incidence (If you're asked to measure this, use a protractor.) 

4) Draw the refracted ray on the opposite side of the boundary. 

   - If the second material is denser, the angle of refraction bends towards the normal and so the angle between the normal and refraction is smaller than the angle of incidence. 

  - If the second material is less dense, the angle of refraction is larger than the angle of incidence. 

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Refraction

Waves travel at differing speeds in materials that differ in density. So when a wave does cross a boundary, the wave changes speed. Once it hits the material, the change of speed causes a change in direction. 

If the wave is travelling along the normal, the wave speed changes, but is not refracted. 

If the wave bends towards the normal, the wave slows down. If the wave bends away from the normal, the wave speeds up. 

Wavefront Diagrams -

Show refraction using wave front diagrams. The space between each wavefront shows the wavelength.

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Sound

Sound waves are longitudinal waves, meaning the vibrations are passed through compressions and rarefactions.

As a sound wave travels through a solid, it causes the particles in the solid to vibrate, however the frequencies that can be transferred through an object depend on the objects size, shape and structure.

Sound waves travel at different speeds through different mediums. For example, sound waves travel quicker through solids than they do in liquids and faster in liquids than they do gases. The frequency isn't affected when transferring from one media to another, but the wavelength does change causing the wave speed to change also. This means that sound waves can be refracted. 

Echoes are caused by sound waves being reflected from hard, flat surfaces. 

Sound waves cannot travel in a vacuum because there are no particles to move or vibrate and carry the wave on. 

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Ear Structure

Sound waves reach your eardrum cause the eardrum to vibrate. These vibrations are continued on by tiny bones called ossicles where they're passed through semicircular canals and into the cochlea. 

The cochlea converts these vibrations into electrical signals (Through the hairs in the ear canal) which are then sent to the brain via the auditory nerve, where the brain interprets the signals at different pitches and volumes, based on the frequency and intensity of the sound. The higher the frequency, the higher the pitch. 

At the beginning of the cochlea, sounds as high a 20,000 Hz are heard here in the thinnest part of the cochlea, known as the base. At the thickest point and the end of the cochlea coil, sounds as low as 20Hz are heard, this is known as the apex.

The hearing of a human is limited to the size and shape of the eardrum, and the structure of the seperate parts of the ear that vibrate to continue the wave. 

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Ultrasound

Ultrasound - Is anysound with a frequency above 20,000 Hz (Above the average human hearing). 

Characteristics of Ultrasound Waves - 

When a wave passes from one media to another, some of the wave is reflected at the boundary between the 2 mediums. This is known as a partial reflection. 

When using an ultrasound producer, you can measure the time it takes for the reflection to reach a detector to measure how far away the boundary is. (Remember to divide this by 2 as the wave travelled there AND back). 

Uses of Ultrasound -

Medical Imagery -

Ultrasound waves can pass through bodily material, but when they meet a differing media (i.e a fluid, such as the amniotic sac), some of the wave is sent back and detected. The timing and distribution of the echoes are processed on to a computer to produce an image of the foetus. 

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Uses of Ultrasound

Medical Imagery -

Ultrasound waves can pass through bodily material, but when they meet a differing media (i.e a fluid, such as the amniotic sac), some of the wave is sent back and detected. The timing and distribution of the echoes are processed on to a computer to produce an image of the foetus. 

Industrial Imagery -

Ultrasound can be used to show faults in objects such as pipes, metal and wood. When an ultrasound wave is passed through the object it is reflected by the far right side of the object, However, if there is a fault or a crack in the object, the wave will reflect much sooner. 

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Infrasound

Infrasound - Any noise that has a lower frequency than 20 Hz (The lowest range of human hearing). 

Some animals, such as elephants and whales, and when these animals produce these sounds to communicate, scientists can detect them and can track these animals for the purpose of conservation. 

Natural occurences such as volcanic eruptions and earthquakes. Scientists can also moniter infrasound in an attempt to predict future events. 

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Seismic Waves

Earthquakes produce waves that travel through the layers of the earth, allowing scientists to explore the structure of the Earth. These are known as seismic waves. 

When there is an earthquake on Earth, it produces seismic waves at a range of infrasound frequencies. Scientists can detect these waves using seismometers, known as Seismologists. They work out the time it takes for waves to reach the seismometer and also note places where the waves do not reach. 

When a seismic wave reaches a boundary between the layers of the Earth, with some waves being absorbed and some waves being refracted. If the waves are refracted, the change in speed causes the waves to bend, but a sudden change in speed causes an abrupt kink in the path. 

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P-Waves and S-Waves

S-Waves -

S-waves are transverse waves and they can only travel through solids. This means that S-waves leave shadow zones as they cannot travel through the liquid core of the Earth. S-waves are much slower than P-waves. 

P-Waves -

P-waves are longitudinal, and can travel through solids and liquids. P-waves also leave shadow zones as they are refracted by the different density of the liquid core of the Earth. P-waves are also much faster than S-Waves.

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Reflection

Law of Reflection - 

Angle of incidence = Angle of reflection. 

The angle of incidence - Is the angle between the incoming wave and the normal at the boundary. 

The angle of reflection - Is the angle between the reflected wave and the normal at the boundary. 

The normal is the line thats perpendicular (90 degrees) to the boundary. To show this in a diagram, use a dotted line. 

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Internal Reflection

A wave hitting a surface may experience a total internal reflection. This only happens when the wave travels through a dense material to a less dense substance. 

If the angle incidence is less than the critical angle - Most of the light is refracted into the outer layer, but some is internally reflected. 

If the angle if incidence is the same as the critical angle - The ray would go along the surafce. 

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Internal Reflection

If the angle of incidence is larger than the critical angle - No light comes out as all the light is internally reflected. 

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Specular and Diffuse Reflection

Specular Reflection - Is when waves are reflected in a single direction by a smooth surface such as a mirror. This means there is a clear reflection. 

Diffuse Reflection - Occurs when waves are reflected by a rough surface such as paper, and so waves are reflected in all directions. This occurs because the normal is different for each incident ray, so each ray has a different angle of incidence (remember the reflection laws). 

This makes the surface look matte, and there isn't a clear reflection. 

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Investigating Refraction (Practical)

Method -

1) Place a transparent rectangular block on a piece of paper and trace around the block. Using a ray box, shine a ray of light at the middle of on side of the transparent block. 

2) Trace the incident ray and the emergent ray on the opposing side of the block. Then, remove the transparent block from the paper, and join up the incident and emergy rays with a straight line. This shows the path of the refracted ray. 

3) Then, draw the normal at the point where the light ray entered the block. (Remember the normal is at a 90 degree angle from the boundary). 

4) Use a protractor to measure the angle of incidence between the normal and the boundary. Then use the protractor again the measure the angle of reflection from the normal and the refraction ray inside the block. 

5) Repeat step 4 for the emergent ray. 

6) Repeat the entire method 3 times to get an accurate average for all the angles.

7) Repeat the experiment using different rectangular blocks of materials keeping the indident angle the same.

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Investigating Refraction

From the experiment you should find that -

1) The ray of light bends towards the normal as it enters the glass block, because the air has a low optical density so the light ray slows down when it enters the block. 

2) As it leaves the block, the light bends away from the normal, because the light ray speeds up. 

3) By repeating the experiment, you should find that the angle of refraction changes for different materials, as they all have different optical densitites. 

4) This experiment uses visible light to see the light rays being refracted, but all electromagnetic waves can be refracted. 

Requirements for Experiment -

1) Because the experiment uses a ray of light, the experiment must be done in a dim room in order to see the ray clearly. 

2) To see the ray of light accurately, the light ray must be thin, so you can easily see the middle of the ray when tracing it. Use a ray box, that has a thin slit is cut into one of the sides of the ray box, to allow a thin ray of light through. 

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Colour

Colour is decided by the differences in absorption, transmission and reflection of different wavelengths by different materials. 

White light is a mixture of all the colours of light, which all have different wave lengths. At the red end of the spectrum, the waves have a long wavelength and a low frequency, whereas at the purple end of the visible light spectrum, waves have a short wavelength and a high frequency. 

Opaque objects are objects that do not transmit light, instead different wavelengths of visible light are absorbed and reflected by the object. The colour of this opaque object depends of which lights are reflected. For example, a red apple reflects red visible light and absorbs all the other colours. 

Colours can be mixed together (With the exception of pure red, blue and green, also known as the primary colours). For example, a Banana may look yellow because its reflecting yellow visible light or reflect blue AND green light. 

White objects reflect all of the colours in the visible light spectrum equally. 

Black objects absorb all wavelengths of visible light, as our eyes seeblack as a lack of visible light. 

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Colour

Transparency - Any object that you can see through completely. 

Translucency - Any object that you can partially see through. 

Any objects that are transparent and translucent can transmit light, meaning that not all light is absorbed or reflected, so some of the visible light waves pass through.

Some wavelengths of light may be absorbed or reflected by translucent objects and sometimes by transparent objects, but not as much.  

These objects will appear to be the colour of light that corresponds to the wavelengths that are most strongly transmitted by the object. 

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Colour Filters

Colour filters are used to filter out different wavelengths of light, so only certain colours are transmitted, with the rest of the colours being absorbed. 

A primary colour filter (Red, Blue and Green) only transmits this single colour. For example, if a white light is shone at a green colour filter, only green light is transmitted, and the other colours are all absorbed. 

Looking at an object that is blue through a blue colour filter will still appear blue. This is because blue light is reflected from the surface of the object and is transmitted by the colour filter. 

On the other hand, looking at a red object through a blue colour filter will make the object appear black as all of the reflected light from the object is absorbed by the filter. 

Filters that aren't primary colours let through the wavelengths of the corresponding colour and the primary colours that are associated with the colours mixture. For example, a cyan colour filter is made from blue and green light mixed. So a cyan colour filter will let through a any wavelength that is cyan, blue and green. 

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Lenses

Lenses - Form images by refracting light and changing the light rays direction. There are two types of lenses - Converging (Convex) and Diverging (Concave) Lenses. 

A Converging Lens - Bulges outwards in the middle of the lens. This causes parallel light rays to converge to the prinicpal focus (The focal point). 

A Diverging Lens - Caves inwards, causing parallel light rays to spread out (or diverge). 

Diagrams - 

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Images

Images - Are formed when all the light rays from a certain point appear to come together. 

A real image - Is formed when light rays come together to form the image. This image is captured on a screen, because the light rays actually meet at the place where the image seems to be. For example, the eye's retina. 

A virtual image - Is when rays from an object appear to be coming from a different place than they're actually coming from. The light rays don't come together at the point where the image seems to be, so it cannot be captured on a screen. For example, magnifying glasses form virtual images. 

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Power of Lenses

Focal length is related to the power of the lens. The more powerful the lens is the more strongly the lens converges rays of light. This means there is a shorter focal length. 

A converging lens has a positive power, whereas the diverging lens has a negative power. 

The curvature of the lens affects the power of the lens. To make a lens more powerful from materials such as glass, you have to make it with a stronly curved surface. 

Some materials are much better at focusing light than others, So more powerful lenses can be made thinner by altering the material that they're made from. 

A material thats better at focusing light means you don't need to make the lenses as curved to get the same focal length. 

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Lenses and Ray Diagrams

Ray Diagram of a Diverging Lens -

1) Pick a point at the top of the object . Draw a ray going from the object to the lens parallel to the axis of the lens. 

2) Draw another line from the same position going through the middle of the lens 

3) The incident ray that is parallel to the axis is refracted, so it appears to come from the principal focus. Draw a ray from the principal focus using a dotted line to show where the virtual image is created. 

4) The ray passing through the middle of the lens doesn't bend. Mark where the ray meets the virtual ray, this is the top of the image. 

A diverging lens always produces a virtual image. The image is always the right way up, smaller than the original object and on the same side of the lens as the object. 

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Diverging Lens Diagrams

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Lenses and Ray Diagrams

Converging Lenses -

1) Pick a point at the top of the object. Draw a ray going from the object to the lens parallel to the axis of the lens. 

2) Draw another ray from the top of the lens that travels through the middle of the axis.

3) The incident ray that is parallel to the axis is refracted through the principal focus. Draw a refracted ray passing through F. 

4) The ray passing through the middle of the axis doesn't bend.

5) Mark where the rays meet, as this shows the top of the object. 

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Converging Lens Diagrams

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Converging Lens Positions

The distance from the lens of an object affects the size and the position of the image. 

Image 1 - 

1) An object that is 2 focal lengths away from the lens will produce a real, inverted image that is the same sizeas the object and at 2F on the other side of the lens. 

Image 2 - 

2) Any object that is between F and 2F from the lens will produce a real, inverted image, that is bigger than the object and beyond 2F. 

Image 3 -

3) Any object that is nearer than F will produce a virtual image that is the right way up, bigger than the object and on the same side of the lens. 

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Converging Lens Images

Image 1 -

Image 2 - 

Image 3 - 

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Electromagnetic Waves

Electromagnetic Waves are a form of transverse wave. All EM waves travel at the same speed through a vacuum, However, they travel at different speeds in different materials leading to dispersion and refraction. 

EM waves vary in wavelength between 10M and 1015 M. These waves are then grouped based on their wavelength and frequency, with seven basic types of EM waves: Radio, Micro, Infrared, Visible light, Ultra Violet, X-Rays and Gamma Rays. These all merged creating a spectrum. 

EM waves are generated by a variety of changes in atoms and their nuclei, giving a large range of frequencies. Changes in the nucleus of an atom create gamma rays and visible light is often produced by changes in an electrons energy level, this explains why atoms can absorb a large range of frequencies. 

All EM waves transfer energy from a source to an observer. An example being, when you warm yourself with an electric heater , infrared waves transfer energy from the thermal energy store of the heater to your thermal energy store. 

If an EM wave has a higher frequency than other EM waves, it is more dangerous as this wave transfers more energy. 

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EM Wave

When EM waves meet a boundary, the waves can be absorbed, transmitted, refracted or reflected. What occurs at a boundary depends on the material that the boundary is made of and the type of EM wave that hits the boundary. 

Properties of EM waves -

Radio - These waves are transmitted through the body without being absorbed. 

Micro - Some wavelengths of microwaves can be absorbed, causing cells to heat up. This may be dangerous. 

Infra and Visible Light - Are mostly reflected and absorbed by the skin, causing some heating. Infrared can cause burns if the skin becomes to hot. 

UV - Is absorbed by the skin. It has a higher frequency than IR and VI so it can be more dangerous. It is also a form on ionising radiation, so when it is absorbed by the skin, it may cause damage to cells on the surface of the skin, potentially leading to skin cancer. It can also damage your eyes. 

X and Gamma Rays - Are highly ionising, so they cause mutations and damage to cells. They have even higher frequencies, so they transfer more energy causing more damage. They can also pass through skin and are absorbed by deeper tissues within the body. 

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EM Wave

When EM waves meet a boundary, the waves can be absorbed, transmitted, refracted or reflected. What occurs at a boundary depends on the material that the boundary is made of and the type of EM wave that hits the boundary. 

Properties of EM waves -

Radio - These waves are transmitted through the body without being absorbed. 

Micro - Some wavelengths of microwaves can be absorbed, causing cells to heat up. This may be dangerous. 

Infra and Visible Light - Are mostly reflected and absorbed by the skin, causing some heating. Infrared can cause burns if the skin becomes to hot. 

UV - Is absorbed by the skin. It has a higher frequency than IR and VI so it can be more dangerous. It is also a form on ionising radiation, so when it is absorbed by the skin, it may cause damage to cells on the surface of the skin, potentially leading to skin cancer. It can also damage your eyes. 

X and Gamma Rays - Are highly ionising, so they cause mutations and damage to cells. They have even higher frequencies, so they transfer more energy causing more damage. They can also pass through skin and are absorbed by deeper tissues within the body. 

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Emitting and Absorbing

ALL objects absorb and emit EM radiation constantly. The distribution and intensity of these wavelengths depends on the object's temperature. The intensity of the emission or absorbed is the power of energy transferred per second (Or power per unit area). 

If the temperature of the object increases, the intensity of each emitted wavelength increases also. However, the intensity increases more rapidly for waves with a shorter wavelength, causing the peak wavelength to decrease. (The peak wavelength = The wavelength with the highest intensity). 

The rate at which an object emits and absorbs EM radiation may also affect its temperature. 

1) If the average power that the object absorbs is more than the average power that the object emits, the object will heat up. 

2) If the average power that the object emits is less than the average power that the object emits, the object will cool down. 

3) An object that is a constant temperature emits and absorbs the same average power. 

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Radiation and The Earth

The temperature of the Earth depends on the amount of radiation that is reflected, absorbed and emitted. 

During daytime, radiation is transferred from the Sun. Some of this is reflected but most of this radiation is absorbed. The absorption and reflection of radiation is caused the the atmosphere, clouds and the surface of the Earth, thus causing an increase in the local temperature. 

During nighttime, radiation is emitted by the atmosphere, clouds and the surface of the Earth, causing a decrease in local temperature. 

Due to the loss and absorbtion of radiation, the Earth's average temperature remains fairly constant. 

However, this Earth's temperature is increasing as changes in the atmosphere can disrupt the balance between absorption and emission of radiation. If the Earth absorbs more radiation than it emits, the average temperature begins to increase, and this will occur until the balance between emission and absorption is mended again. 

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Emission and Absorption - Core Practical

Investigation - How well different surfaces emit radiation. 

Method -

1) Wrap four identical test tubes with different coloured and surfaced materials. Keep the material the same (For example, paper) but change the colour and surface for each test tube (Use black, white, glossy and matte paper). 

2) Boil the kettle and fill each test tube with the same volume of boiled water. 

3) Put a thermometer in the test tube to measure the temperature of the water in the test tube every minute. To prevent heat loss through the top of the test tube, cover the test tube with a bung between the temperature measurements. 

Predictions -

The temperature of the water will decrease quicker in the test tubes covered by surfaces that are good emitters. (Black, Dull surfaces are the best emitters.) Shiny, white surfaces are good absorbers of radiation and so they emit less radiation. 

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EM waves and Communication

EM waves are made up of oscillating electric and magnetic fields. Alternating currents are made up oscillating charges, and as the charges oscillate they produce electric and magnetic fields. The frequency of the waves produced are equal to the frequency of the a.c current. 

Radiowaves -

You can produce radiowaves using an a.c current in an electrical circuit. The object in which charges oscillate to create radio waves is called a transmitter. When transmitted radiowaves reach the receiver, the radiowaves are absorbed. 

The energy carried by the waves is transferred to the electrons in the material of the receiver, and this energy causes the electrons to oscillate. If the receiver is part of a complete electrical circuit, it will generate an a.c current. 

This current, as said earlier, has the same frequency of the radiowave that generated this frequency. 

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Radiowaves and Communication

Long Wave Radio - (Wavelengths between 1-10km) can be received halfway around the world from the source. This is because long wave radiowaves can bend around the curved surface of the Earth. This is useful for radio signals to be received even if the receiver isn't in sight of the transmitter. 

Short Wave Radio - (Wavelengths between 10-100m) can be received long distances from the transmitter but not as far as Long Wave Radio. They can travel long distances as they're reflected by the Earth's atmosphere. For example, Bluetooth uses short wave radiowaves to send information over short distances between different devices without any wiring. 

Radiowaves for TV's and FM radio are very short and to receive a signal, they must be in the direct line of sight of the transmitter. 

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Microwaves and Radiowaves

Communication to and from satellites uses EM waves which can easily pass through the Earth's watery atmosphere. These waves are more commonly microwaves but can also be high frequency radiowaves. 

For a satellite TV, the signal from a transmitter is transmitted into space and is picked up by a satellite receiver dish orbiting thousands of kilometers above the Earth. 

The Satellite transmits a signal back to Earth in a different direction, where it is then received by a satellite dish on the ground. 

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Microwaves

Microwave Ovens -

In microwave ovens, the microwaves need to be absorbed by the water molecules in food (Different wavelengths of microwaves are used in communications and food). 

The microwaves penetrate a few cm deeper into the food before being absorbed and transferring the energy that they're carrying to the water molecules in the food, causing the water to heat up. 

The water molecules then transfer this energy to the rest of the food molecules by heating, which quickly cooks the food. 

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Infrared Radiation

IR radiation is given out by all hot objects - the hotter the object is the more infrared radiation that the object gives out.

Infrared cameras can be used to detect infrared radiation and monitor temperature. The camera detects this radiation and then turns the information into an electrical signal, which can then be displayed on a screen (Also known as thermal imagery). Thermal imagery is used by police in order to see suspects that are attempting to escape or hide in the dark. 

Infrared sensors can also be used by security systems. If infrared radiation is detected, an alarm sounds or a security light turns on. 

Absorbing IR radiation causes objects to heat up. Food can be cooked using IR radiation. 

Electric heaters heat up a room in a similar way. Electric heaters contain a long piece of wire that heats up when a current flows through it This wire emits IR radiation (and visible light - which is what we see when the wire begins to glow). The emitted IR radiation is absorbed by objects and the air in the room, as energy is transferred by the IR waves to the thermal energy stores of the objects, causing a temperature increase. 

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Infrared Information

Infrared radiation can be used to transfer information. For example, it can be used to send files between mobile phones or laptops, however this distance must be very small and the receiver must be in the line of sight of the transmitter. This is also how a TV remote functions. 

Optical fibres are thin glass or plastic fibres that carry data over long distances in the form of a pulse of IR radiation. They usually use a single wavelength to prevent dispersion which can lead to a loss of information. They use total internal reflection to send multiple pieces of data over a long distance. 

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Uses of EM Waves

Visible Light -

Photographic film reacts to light to form an image. This is how traditonal cameras create a photograph. Digital cameras contain image sensors, which detect visible light and generate en electrical signal. This signal is then converted into an image that can be digitally stored or printed. 

Gamma Rays -

Gamma Rays are used to sterilise medical instruments as they kill microbes. Food can be sterilised in a similar way, keeping food fresh for longer without needing to freeze it, cook it or preserve it. 

Some medical imagery such as tracers contain gamma rays to detect cancer, and gamma rays are often used as cancer treatment also. Radiation is targeted at cancer cells to kill them, Doctors must be careful to minimise the damage to healthy cells when using these techniques. 

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UltraViolet

Fluorescence is a property of particular chemicals, where UV radiation is absorbed and then visible light is emitted, making fluorescent colours look bright. 

Fluorescent light use UV to emit visible light, They're energy efficient and they're good when light is needed for long period of times (For example, classrooms.) 

Security pens can be used to mark property. Under a UV light, the ink will glow, but it is otherwise invisible, which is useful in identifying stolen property. 

Banknotes and passports use a similar technique to prevent forgeries, as genuine notes have special markings that only appear under UV light. 

UV is also sometimes used to sterilise water, which kills bacteria in the water making it much safer to drink. 

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X - Rays

X-rays are used to view the internal structure of objects and materials including human bodies. 

They affect photographic film the same way as visible light, allowing us to have x-ray photographs. But x-ray images are usually formed electronically. 

Radiographers in hospitals take X-ray images in order to help doctors diagnose broken bones. X-rays are transmitted by flesh but are absorbed by denser material such as bones. 

In order to produce an x-ray image, x-ray radiation is directed through the object or body onto a detector plate. The brighter bits of the image are where fewer X-rays get through, producing a negative image. 

X-rays are also used in airport security systems to detect hidden objects that cannot be detected with metal detectors. 

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