What are waves used for?
Waves are used to transfer energy and information.
• Transverse waves vibrate at right angles to the direction of the energy transfer of the waves • All electromagnetic waves are transverse waves
• Longitudinal waves vibrate parallel to the direction of the energy transfer of the waves • An example of a longitudinal wave is a sound wave
Mechanical waves need a medium to travel through, these waves may be transverse or longitudinal. Examples of mechanical waves are sound, water and seismic waves.
What is the amplitude of a wave?
The amplitude of a wave is the height of the wave crest or the depth of the wave trough from the position at rest. The bigger the amplitude of the wave, the more energy the wave carries.
What is the wavelength of a wave?
The wavelength of a wave is the distance from one wave crest to the next wave crest.
What is the frequency of a wave?
The frequency of a wave is the number of wave crests passing a point in one second.
Wave speed equation:
Wave speed (m/s)= frequency (Hz) x wavelength (m).
What is the normal on a mirror?
The normal at a point on a mirror is a line drawn perpendicular to the mirror.
Reflection of a light ray by a plane mirror:
• The angle of incidence is the angle between the incident ray and the normal • The angle of reflection is the angle between the reflected ray and the normal
What does the law of reflection state?
The angle of incidence= the angle of reflection.
What is refraction?
Refraction is the change of direction of a wave when it travels across a boundary.
When a light ray refracts from air into glass (less dense to more dense medium), what happens?
The angle of refraction will be less than the angle of incidence, as it refracts TOWARDS the normal.
When a light ray refracts from glass to air (more dense to less dense medium), what happens?
The angle of refraction will be greater than the angle of incidence as the light ray will refract AWAY from the normal.
What is diffraction?
Diffraction is the spreading out of waves when they pass through a gap or round the edge of an obstacle.
Fill in the missing word: The narrower a gap, the ... the diffraction is.
Why do some people receive poor radio and TV reception?
If the radio waves do not diffract enough when they go over hills, the reception will be poor.
Example of a use of diffraction:
Diffraction of ultrasonic waves is an important factor in the design of an ultrasonic scanner. The ultrasonic waves spread out from a hand-held transmitter and reflect from the tissue boundaries inside the womb.
What is the frequency range of the normal human ear?
The range is 20Hz-20000Hz.
What are sound waves?
Sound waves are vibrations that travel through a medium (substance). They cannot travel through a vacuum (space).
How do echoes occur?
Echoes are due to sound waves being reflected from a smooth and hard surface.
What will happen if sound approaches a wall covered in soft fabric?
The soft fabric will absorb the sound instead of reflecting it.
What happens if the 'loudness' of a sound is increased?
The amplitude of the wave will increase too.
What will happen if the frequency of a sound is increased?
The pitch of the wave will increase too.
How are sound waves produced by an instrument?
Vibrations created in an instrument when it is played produces sound waves.
Law of reflection:
Refraction of light: