Light and Sound Flashcards
Unit for angles
Degree (°)
Unit for frequency
Hertz (Hz)
Unit for length
Metre (m)
Unit for speed/velocity
Metre/second (m/s)
Unit for time
Second (s)
What type of waves are light waves and what can they do?
Transverse waves and the can all be reflected and refracted
What is the law of reflection?
The angle of incidence = the angle of reflection
What happens when images are reflected in a plane mirror?
They are laterally inverted
Images are upright
Same size of the object
The image is virtual
What is a diffuse reflection?
When light hits an uneven surface (like paper) light reflects at different angles
What is the normal?
Imaginary line that’s perpendicular to the surface at the point of incidence
What is the angle of incidence?
Angle between the incoming wave and the normal
What is the angle of refraction?
Angle between reflected wave and the normal
How do waves travel through objects of different densities?
EM waves travel slower in denser media (usually)
Sound waves travel faster in denser media
What is refraction?
The change of wave speed as light travels between media of different optical densities
What is refractive index?
Is the measure of change of wave speed in a material
What is the speed of light in a vacuum?
3x10^8 m/s
How to calculate the refractive index (using refractive index, speed of light in a vacuum and speed in a medium)?
Refractive index = speed of light in a vacuum/ speed of light in a medium
n = c/v
Does refractive index have a unit?
Refractive index is dimensionless (no unit)
What is snells law?
n1sinθ1=n2sinθ2
How to calculate refractive index (using refractive index, sin(i), sin(r)?
Refractive index = sin(i)/ sin(r)
Investigate the refraction of light, using rectangular blocks, semi-circular
blocks and triangular prisms:
Draw around the block on piece of paper and draw normal on the block
Using a ray block shine the light into the normal at the angle required
Draw where the emergent ray comes out of the block
What is dispersion?
It’s the splitting of white light into component colours
Investigate the refractive index of glass, using a glass block:
Draw around glass block and draw the normal
Mark out different angles for the incident ray
Then use a ray box and shine line at the different angles and mark emergent ray
Remove block and draw refracted ray (in the box)
Measure ‘i’ and ‘r’ from the normal
Plot a graph sin(i) against sin(r), straight line, gradient gives refractive index
How could you improve this “investigate the refractive index of glass, using a glass block” experiment?
Repeat experiment and average the results
Turn off lights in the room
What is TIR?
When light is reflected internally so no light comes out of the object
What does θc equal?
The critical angle
What is the critical angle?
It’s the angle of incidence when the angle of refraction 90°
Why do we use semicircular glass?
So the light is incident perpendicularly and doesn’t bend along it’s path
What is the calculation for the critical angle using snells law?
Critical angle = 1/refractive index
sinθc = 1/n
What is the most common application of TIR?
Fibre optic cables
What are fibre optic cables made of?
Plastic or glass with central core surrounded by cladding
Why is the core of fibre optic narrow?
So narrow light signals passing always hit the core-cladding so it’s TIR.
What is the refractive index of air?
1
How does TIR work with prisms?
The ray of light travels into one prism where it’s TIR at 90, the light travels to another prism where the light is TIR at 90°, this allows us to see an object (periscope)
What type of waves are sound waves and what can they do?
Longitudinal and it can be reflected and refracted
What is the frequency range for human hearing?
20-20,000Hz
How would you investigate the speed of sound in air?
Using a oscilloscope, two microphone to find the wavelength of sounds
Start with two microphones next to the speaker, move one away until two waves are aligned on the display which are one wavelength apart
Measure distance between the microphones
Use the formula v = f x λ
What is the frequency of ultrasound?
Above 20,000Hz
What are the applications of ultrasound?
Foetal monitoring
Checking welds
What is the screen of an oscilloscope divided into?
1cm x1cm squares
What is the y-axis of an oscilloscope called?
The (voltage) gain or V/cm
What is the a-axis of an oscilloscope called?
The time base
What is the time base?
The time taken for the trace to cover 1 square
What is the time base set to on an oscilloscope?
5 Milliseconds (0.005s)
How does the amplitude of the wave correlate to the amplitude?
The greater the amplitude the more energy it carries, this means it will be louder
What does frequency mean?
The number of complete vibrations each second
What does the higher the frequency mean for vibrations
The higher frequency means more complete vibrations per second
