# Waves

Waves in general.  Light and Sound.  Longitudinal.  Transverse.  The electromagnetic spectrum.  Ultrasond.  Visible Light.

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• Created by: Rianne B
• Created on: 16-07-12 18:47

## Waves in General

Amplitude is the height of the wave from the middle (equilibirum position) to the top (peak or crest).  Measured in cm or m.

Wavelength is a distance between two identical points on a wave.  Measured in cm or m.

Time Period is the time it takes for one complete wave to pass a point.  Measured in seconds.

Frequency is the number of waves passing a given point in one second.  Measured in Hertz.

The Wave Equation

wave speed = frequency x wavelength

Unsing the f and wavelength of a wave allows us to calculate the speed.

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## Light and Sound

Light

• can travel through a vacuum at 300,000,000m/s
• transverse

Sound

• needs a medium
• longitudinal
• travels at 340m/s in air
• ﻿

Both

• transfers energy from one point to another.
• can refract
• can reflect
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## Longitudinal and Transverse

A longitudinal wave is one where the particles oscillate in the same direction as the wave.

An example of a longitudinal wave is sound wave.

A transverse wave is one where the particles oscillate at right angles to the wave direction.

An example of a transverse wave is sea wave.

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## Ultrasound

Humans can hear sounds that are only higher than 20Hz but lower than 20000Haz.  The range becomes narrower as we grow older.  Your ear gets damaged by the soundwaves.  It loses its sensitivity.

Ultrasounds are when a sound is produced but cannot be heard by human beings.  It is greater than 20000Hz.

Dolphins are ultrasound and so do elephants.  Reflected sound can be used to tell ships about the depth of the sea beneath them.  This is also known as echo sounding.

A ship sends out an ultrasound wave, when in the water.There is also a remote which can tell you how far away from the wall you are.

Ultrasound - premature babies.  Ultrasound is preferred because x-rays can put the mother's life in danger and the baby too.

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## Visible Light

• lowest frequency is red and shortest wavelength is violet.

if the amplitude is increased then the sound becomes louder.  if reduced the sound becomes quieter.

if frequency is increased the sound is at a high pitch.  if reduced sound is at a low pitch.

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## The Electromagnetic spectrum

The Electromagnetic spectrum is a continuous spectrum of waves, which include the visible spectrum.  Properties in common:

• They all transfer energy
• They are all transverse waves
• They all travel at the espeed of light in a vacuum
• They can all be reflected, refracted and diffracted.

Radio   Micro   Infrared   Visible   Ultraviolet   X - rays   Gamma

lowest energy ----------------------------------------------------------- highest energy

longest wavelength ----------------------------------------------------- shortest wavelength

lowest frequency ---------------------------------------------------------- highest frequency

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## The electromagnetic spectrum

Microwaves - mobile phone and satellite communication, cooking

Infrared - infrared cookers and heaters, TV and stereo remote control, night vision

Visible light - seeing commuication (optical fibres), photography

UV - flourescent tubes and UV tanning lamps

X-rays - x-radiography to observe the internal structure of objects.

Gamma - sterilising equipmenta dn food, radiotherapy.

Radiowaves and visible light are not harmful.  Microwaves can cook your internal organs.  Infrared can burn your skin.  UV can blind you and cause cancer.  X-rays can kill you if they are too harmful.  Gamma causes cancer.

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## Ouestions on the electromagnetic spectrum

1. Why does food cook quicker in a microwave oven than a conventional oven?   A microwave oven heats up the food(water) inside which makes it cook from inside out, whereas the conventional oven is the opposite.

2. Explain what would happen if a jacket potato wrapped in silver foil is placed in a microwave oven.   The waves would reflect off the metal and cause it to spark.  The potato would not cook.

3. Why are microwave ovens made of metal?  Microwave ovens are made of metal because it keeps the microwaves in but some can escape.

4. What effect do microwaves have on living tissues?   The microwave would heat your tissue from the inside out.

5. What effect does too much infrared radiation have on the skin?   Infrared can make your skin burn, make it go red.

6. What effect does UV radiation have on the skin?   It can cause cancer.

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## More questions

7. Why do you need to wear goggles on a sun bed?  To stop blindness.

8. Why is there a greater incidence of skin cancer in Australia than the UK?   The hole in the ozone layer causes the UV light to get through and since Australia is closer to it than the UK, they get affected more.

9. Why does a radiographer leave the room or stand behind a lead screen when taking x - rays?  So that they are not exposed to x - rays.

What are the harmful effects of exposure to Gamma rays?  damages, kills living cells, cell mutation and can cause cancer.

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## More questions

7. Why do you need to wear goggles on a sun bed?  To stop blindness.

8. Why is there a greater incidence of skin cancer in Australia than the UK?   The hole in the ozone layer causes the UV light to get through and since Australia is closer to it than the UK, they get affected more.

9. Why does a radiographer leave the room or stand behind a lead screen when taking x - rays?  So that they are not exposed to x - rays.

What are the harmful effects of exposure to Gamma rays?  damages, kills living cells, cell mutation and can cause cancer.

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## More questions

7. Why do you need to wear goggles on a sun bed?  To stop blindness.

8. Why is there a greater incidence of skin cancer in Australia than the UK?   The hole in the ozone layer causes the UV light to get through and since Australia is closer to it than the UK, they get affected more.

9. Why does a radiographer leave the room or stand behind a lead screen when taking x - rays?  So that they are not exposed to x - rays.

What are the harmful effects of exposure to Gamma rays?  damages, kills living cells, cell mutation and can cause cancer.

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