# P1.5 Waves

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## P1.5 Waves

Wave basics

• The amplitude is the displacement (the shortest distance) from the rest position to the crest
• The wavelength is the length of a full cycle of the wave eg crest to crest or trough to trough
• Frequency is the number of complete waves passing a certain point per second OR the number of complete waves produced per second
• Frequency is measured in Hertz (Hz)
• 1 Hz is 1 wave per second
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## P1.5 Waves

Wave basics

• Transverse waves (a) have sideways vibrations - the vibrations are at 90 degrees to the direction of energy transfer of the wave
• Light is an example of a transverse wave
• Longitudinal waves (b) have vibrations along the same line - the vibrations are parallel to the direction of energy transfer of the wave
• Sound, ultrasound and shock waves are examples of longitudinal waves
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## P1.5 Waves

Wave formula

Example: A radio wave has a frequency of 92.2 X 10   Hz. Find its wavelength. The speed of all radio waves is 3 X 10   m/s

Solution: wavelength = velocity / frequency

= 3 X 10   / 92.2 X 10

= 3.25m

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## P1.5 Waves

Reflection

Angle of incidence = Angle of reflection

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## P1.5 Waves

The image formed in a plane mirror

The image formed in a plane mirror is:

• the same size as the object
• as far behind the mirror as the object is in front
• virtual (cannot be projected on to a screen)
• upright
• laterally inverted (right side of object appears to be the left side of the image and vice versa
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## P1.5 Waves

Diffraction of waves

• The amount of diffraction depends on the size of the gap relative to the wavelength of the wave
• The narrower the gap or the longer the wavelength, the more the wave spreads out
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## P1.5 Waves

Refraction

• As the light passes from air into glass it bends (refracts) towards the normal
• As the light passes from glass to air it bends (refracts) away from the normal
• Waves are only refracted if they meet at an angle
• If they are travelling along the normal (the angle of incidence is zero) they are not refracted
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## P1.5 Waves

Electromagnetic Spectrum

• EM waves with different wavelengths (or frequencies) have different properties
• All the different types of EM wave travel at the same speed in a vacuum
• EM waves with higher frequencies have shorter wavelengths
• Different EM waves have different properties and therefore different uses
• EM waves have different uses for communication because of their different wavelenths
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## P1.5 Waves

Radio waves are used mainly for communication

• Long wavelength radio waves diffract around the curved surface of the Earth. They can also get around hills and into tunnels
• Short wave radio signals can be received at long distances from the transmitter. This is because they are reflected by the Earths electrically charged upper atmosphere, the ionosphere (diagram)
• To receive TV and FM signals, there must be nothing between the aerial and the transmitter - the signal will not bend around hills or travel far through buildings
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## P1.5 Waves

Microwaves are used for satellite communications and mobile phones

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## P1.5 Waves

Infrared waves are used for remote controls

Remote controls work by emitting different patterns of infrared waves to send different instrutions to an appliance

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## P1.5 Waves

Visible light is used for photography

• Cameras use a lens to focus visible light onto a light-sensitive film or electronic sensor
• The lens aperture controls how much light enters the camera
• The shutter speed allows you to control how long the film or sensor is open to the light
• The longer the film or sensor is open to the light, the more light that will enter the camera and react with the film
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## P1.5 Waves

Sound travels as a wave

• Sound waves are caused by vibrating objects
• The vibrations are passed through the surrounding medium eg air as a series of compressions
• Sound waves are a type of longitudinal wave
• Sound cannot travel in a vacuum (no particles)
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## P1.5 Waves

The high the frequency, the higher the pitch

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A really good set of revision notes to support this AQA unit. Includes diagrams to help aid understanding.

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i angery

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S o m e o n e   d o e s n ' t   k n o w   h o w   t o   s p e l l

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this has helped me I recommend it to other people

thank you

this has helped get in to my head the important things for my exam

thank you

Ryan shemwell

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revision K

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