# Physics - Rays and Waves

This set is for IGCSE Physics, specifically Rays and Waves, this topic has 5 subtopics which are:

Light Rays and Waves          Reflection          Refraction         Total Internal Reflection           Electromagnetic Waves

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## Light Rays and Waves

We see objects by light reflecting off of them.

Light:

Travels in straight lines.

Travels in waves, therefore transfers energy and information without transferring matter.

Can travel through an empty space.

Is the fastest this that there is travelling at 300000 km / s.

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## Reflection

When light is reflected there are two rays, the incident ray and the reflected ray. There is also the normal which is a hypothetical line, 90 degrees of the surface reflecting the light.

THe two laws of reflection are:

The angle of incidence = The angle of reflection

The incidence ray, the reflected ray and the normal lie in the same place.

There are three rules for the size and position of the image which are:

The image is the same size as the object.

The image is as far behind the mirror as the object is in front of it.

A line joining the object and image go through the mirror at right angles.

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## Refraction

Refraction is where light waves travel slower in a different medium (like glass of water) than in air. Therefore the light is bent.

The speed of light in a medium (refractive index) is found using this equation:

refractive index = (sin x angle of incidence) / (sin x angle of refraction) or n = sin i / sin r

If light is refracted through a prism them it is deviated.

This is where it travels fast through air, then slow through the glass, then dispersed as it comes out the other end showing all the colours of the spectrum.

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## Total Internal Reflection

The critical angle is the angle where a light ray goes through glass and the refracted ray is 90 degrees to the glass surface.

Total internal refraction is where the light comes at such an angle to the glass that it is not refracted by reflected.

The critical angle is worked out using this equation:

sin x critical angle = 1 / refractive index or sin c = 1 / n

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## Electromagnetic Waves (1)

Electromagnetic waves all:

have the same wavespeed.

travel at the speed of light.

As you go through the electromagnetic spectrum the wavelength decreases and the frequency increases. This is the electromagnetic spectrum in order:

Radio Waves --> Microwaves --> Infrared --> Visible Light --> Ultraviolet --> X-rays --> Gamma Rays

Radio waves are used for TV and radio transmition as their waves are long so can diffract around hills.

Microwaves are used for transmissions, also for heating so they are also used in cooking. However, they can also cause internal heating of body tissues so can be dangerous.

Infrared can be picked up so can be used to see object emitting heat that can't be seen using light. There are also alarms and lamps that pick up infrared and go off.

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## Electromagnetic Waves (2)

Light is used for photography and images.

Ultraviolet is picked up by some materials which can then be put on money notes, passport e.t.c. to prove that they are genuine, also they can be used as sterylisers. However, they cause harm to living cells and can cause blindness.

X-rays can be used see bones as they go through skin however are stopped by bone, concerntrated beams can also kill cencerous cells. However, in large doses they can cause cancer or mutation.

Gamma Rays are used for sensors, sterylisers and treatment of cancer, however they can also cause cancer as well.

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