P4 - Properties of waves, including light and sound Flashcards
Waves have a
wavelength, frequency, amplitude, and time period.
What is the wavelength of the wave
it is the distance between two adjacent peaks or troughs of waves.
What is frequency
Frequency is the number of complete waves that go past each second (Hz)
What is the amplitude
in a water wave it is the maximum displacement of the water from an undisturbed position.
What is speed of wave
the distance the wave travels in 1 s.
What does the speed of a wave depend on
- The substance
2. The medium the wave is passing through
Waves transfer energy from one place to another without
transferring matter
What is wave motion
The movement of a wave
Wave motion can be shown by
- vibrations of a spring
Hold one end of a horizontal spring in a fixed position and move the other end of the spring up and down
We can observe a wave moving from the end we are holding towards the fixed end of the spring
- water wave
When a wave travels along the surface of a water, a cork floating on the surface will only move up and down as waves pass.
What is a wavefront
it is a moving line that joins all points on the crest of a wave
What are the two types of waves
longitudinal and transversal waves
In a longitudinal wave vibrations are
in the direction of travel of the wave.
It can be shown by pushing and pulling a spring
The stretching of a sling produces
regions of rarefaction (where the coils spread out) and regions of compression (where the coil is squashed).
What is an example of a longitudinal wave
sound
How is the wavelength found in a longitudinal wave
- Where the distance between two consecutive points of maximum compression
- Distance between two consecutive points of minimum compression.
In a transverse wave vibrations are
at right angles to the direction of wave travel.
It can be shown by moving a spring side to side
Examples of transverse wages
Light
radio and other electromagnetic waves
What are the similarities of transverse and longitudinal waves
Similarities
- Both made up of vibrations
- They both are waves that have repeating shape or pattern
The speed of a wave in a given medium is
constant
What is the equation for wave speed
wave speed (m/s) = frequency (Hz) x wavelength (m)
Reflection happens when
a wave hits a flat surface (plane) and bounces off it
Refraction is when a
waves speed can change when moving from one medium to another.
When a wave crosses a new medium at an angle
the change in a wave’s speed will cause the direction of the wave’s motion to change and the wave will appear to bend
What is diffraction
when a wave reaches a narrow gap in a surface they will continue to travel through that gap and change shape.
If the gap size is relatively large compared to the wavelength the wave passes
with little diffraction
If the gap size is relatively small compared to the wavelength the amount of diffraction
increases and not much of the waves will pass through.
Diffraction is strongest and most noticeable when
the width of the gap is similar in size to the wavelength of the wave.
The angle of the incidence is the angle
between the incident (incoming) light ray and the normal
The normal is
perpendicular (90) to the surface of the plane
The angle of reflection is the angle
between the reflected light ray and the normal
What does the law of reflection state
that an angle of incidence = the angle of reflection
When a wave slows down
the wavelength gets smaller
A wave slows down as it travels across the boundary to a
denser medium
If frequency of a wave does not change crossing the boundary and the speed creases the wavelength must
also decrease
When a wave speeds up
the wavelength gets larger
If speed increases but frequency stays the same the wavelength must
also increase
Why does light not need a medium to travel through
Because it is an electromagnetic wave
When you look in a plane mirror the image you see is called
laterally inverted (left and right sides are exchanged)
What is a virtual image
is something that cannot be projected onto a screen
Light waves slow down when they travel from
air to glass
When a light ray is at an angle to a glass it
bends toward the normal as they enter the glass
When light rays travel out of the glass into air their speed
increases and they bend away from the normal
What is the refractive index
it indicates how much the material changes the direction of the light
What is the equation of the refractive index
n = sin i/ sin r
The refractive index of a vacuum is
1
what is another equation of the refractive index
n = speed of light in vacuum (or air) / speed of light in the material
When rays of light pass from a dense medium to a less dense medium they
bend away from the normal
the angle of incidence at which the angle of refraction becomes equal to 90 is called the
critical angle
when the angle of incidence surpasses the critical angle the angle of refraction
reflects back inside the material
What is total internal reflection
when the angle of incidence is greater than the critical angle so the rays are entirely reflected back inside the medium
critical angle formula
n = 1/sin c
total internal reflection is used in
fibre optic cables
Light does not escape from the fibre because
it always hits the internal surface at an angle greater than the critical angle and is internally reflected
Why are fibre optic cables useful and used
They do not use electricity so signals can be carried by infrared waves and do not suffer interference.
They are cheaper than copper cables and can carry thousands of different signals down the same fibre
Bundles of several thousand optical fibers used in medical endoscopes for internal examination of body
