4 Light and Sound Flashcards
This is a longitunidal wave.
Locate the compressions and rarefactions
When measuring an angle of incidence, what is the most common error?
Angle of incidence is not 56°
Angle of incidence is between the incident ray and the normal
90° - 56° = 34°
incident angle = 34°
In bike reflectors, explain how TIR allows light to be bent by 180° and reflected straight back out.
- light enters block at 0° - no refraction
- light reaches back boundary at 45°
- 45°> the critical angle
- TIR occurs
- light reaches next boundary at 45°
- 45°> the critical angle
- TIR occurs
- light strikes front face of reflector at 0° (no refraction) and emerges parallel to incident ray
What type of wave is visible light?
transverse wave- oscillations are 90° to direction of travel
What is the order of the visible spectrum?
red
orange
yellow
green
blue
indigo
violet
What shows that the chirp of each bird is the same pitch?
same number of waves in the same time
same frequency
Ultrasound is used in echo finding. Give one example of how human use ultrasonic echoes.
Trawlers send ultrasonic pulses into the ocean and time how long it takes for a reflection to return from the ocean floor.
distance = speed of sound in water (1500m/s) x time of echo
depth of ocean = depth / 2
What is the frequency of sound?
Number of vibrations per second
measured in Hertz Hz
Why does sound travel faster in solids compared to gases?
- Solids have stronger forces between particles compared to gases
- particles are closer together in a solid compared to a gas
- It is easier for vibrations to be passed between particles in a solid compared to a gas
An endoscope is one use of visible light. Light is sent down an optical fibre and an image of internal organs can be viewed by a doctor.
What prinicple of light does this application use?
TIR or total internal reflection of light
What happens to the speed, direction and wavelength of light when it enters a more dense medium at an angle to the normal?
Light slows down, the waves bunch up and the wavelength decreases, the waves change direction- bend towards the normal.
Frequency stays the same.
What property of a sound wave indicates the loudness of the sound?
amplitude
Binoculars use TIR to bend light through prisms and direct it to the back of the eye. Explain what happens in each prism?
angle of incidence = 45°
greater than critical angle of prism
Therefore TIR occurs
If incident angle = 45°, then reflected angle= 45°
Therefore light is bent a total of 90°
What is the equation linking critical angle and refractive index?
What is the unit for pitch of sound?
Hertz Hz
pitch = frequency
How is sound different from visible light?
sound is a longitudinal wave, light is a transverse wave
sound cannot travel through a vacuum, light can
sound travels much slower in air (340 m/s), light is much faster at 300 000 000 m/s
What type of wave is a sound wave?
Longitudinal
oscillates parallel to direction of wave travel
If reflection is light bouncing, what is refraction?
Refraction is light bending (changing direction)
Determine the amplitude of the wave.
volts per division = 5 V/ div
amplitude = 2 division
2 divisions x 5V/division= 10V
What is the angle of refraction
the angle between the refracted ray and the normal
Label the wavelength of the sound wave below
distance from middle of one compression to the middle of the adjacent compression.
compression to compression
What happens when light strikes a black object
All light is absorbed
Why does the light totally internally reflect down the glass tube?
As light travels from more optically dense to less optically dense mediums
and
The angle of incidence is greater than the critical angle, therefore TIR occurs
What happens to the speed, direction and wavelength of light when is enter a less optically dense medium?
Light speeds up
the wavelength increases
the waves bend away from the normal
Frequency stays the same
Which sound has the higher frequency?
Mouse has a higher frequency sound
More waves per second
How does the following analogy of soldiers marching in rank from concrete to mud help explain refraction.
- soldiers slow down when going into mud, light slows down when going into a more optically dense medium
- rows of soldiers bunch up when in the mud, wavelength of light decreases when light enters more optically dense medium
- direction of soldier bends towards the normal when they enter the mud, ray of light bends towards the normal when entering a more optically dense medium
How can you calculate the refractive index from the following graph?
The gradient of a sin i against sin r graph equals the refractive index
gradient = 0.9/0.5 = 9/5 = 1 and 4/5 = 1.80
n = 1.80
Reflections in Maths are the same as reflections in a plane mirror in Physics.
Where is the mirror located if the object is triangle ABC?
The mirror is located at the x axis
How is frequency and time period related?
frequency = 1 / time period
time period = 1 / frequency
Determine the frequency of the wave.
time base = 0.5 s/ division
peak to peak = 4 divisions
Time period = 4 x 0.5s / division = 2s
f = 1 / time period = 1/2 = 0.5 Hz
How can the echo method be used to measure the speed of sound through air?
- Stand 170 m from large wall or cliff face.
- begin clapping at constant rate and listen for echo
- speed up or slow down rate of clapping until your clap is at same time as you hear the echo. (sound travels there and back between claps = 340m!!)
- time 10 full claps. (340m x 10 = 3400 m)
speed = 3400m / time
(time should be 10 second as 3400 m / 10 s = 340 m/s)
Out of the liquids listed below, which will bend light the most?
Sodium chloride will bend light the most because it has the largest refractive index.
How can you measure the speed of sound through air in a laboratory?
- Use microsecond timer connected to two microphones which are places 2.00 metres apart (using metre rules)
- make sound (hammer on metal) behind first microphone
- first microphone starts timer
- second microphone stops timer
- repeat 5 times and find mean
speed of sound = 2.00 m / average time
Diamond has a very high refractive index of 2.40. This means that the critical angle is very small at 25°.
Why does this make diamond sparkle?
TIR occurs when i > critical angle
If the critical angle of diamond is only 25°, then more light is reflected within the diamond.
Diamonds are cut into a shape which allows light entering the top of the diamond to reflect within it and emerge back through the top - making it sparkle!
In terms of TIR, what is the critical case?
When light is shining from a more optially dense medium to a less optically dense medium at exactly the critical angle.
the light will run along the boundary with a refracted angle of 90°
Determine the amplitude of the wave.
volts per division = 2 V/ div
amplitude = 2 division
2 divisions x 2V/division= 4V
Determine the time period of the wave.
time base = 10 microseconds / division
10 x 10-6 s
peak to peak = 3.3 divisions
(crest to crest)
T= 3.3 div x 10 microseconds/ div= 33 microseconds
33 x 10-6 s
What is the critical angle?
The critical angle is the largest angle of incidence for which refraction can still occur.
What are the issues with measuring speed of sound in air using a starting pistol and stopwatch?
How can the method be improved?
- large reaction time using stopwatch
- time reading can be very small and so this creates large percentage error in time readings
Improvement:
Larger distances can be used with increases the time reading and reduces the percentage error (distance > 200m is best)
Determine the time period of the wave
time base = 10 ms/ division
Peak to peak = 3.2 divisions
time period = 3.2 x 10 ms = 32 ms
