Light and Sound Flashcards
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°
What type of wave is visible light?
It is a transverse wave- oscillations are 90° to direction of travel
What is the order of the visible spectrum?
red
orange
yellow
green
blue
indigo
violet
You can find the refractive index of a block by following these instructions. What equipment is needed and what must be measured and calculated?
- Place the rectangular block in the centre of the paper and carefully trace its position
- Shine ray of light from ray box at an angle to the air/glass boundary
- Mark incident ray and emerging ray with two crosses using the pencil
- Remove the block and using a ruler trace the incident ray and emergent ray up to the air/glass boundary
- Join the points where the light entered and left the block, and draw a normal using a protractor.
Equipment: ray box, rectangular block of glass, paper, pencil, ruler, protractor
- Measure the incident and refracted angle using the protractor.
- Calculate the refractive index n = sin i/ sin r
- Repeat steps 1-6 for different angles, calculate the refractive index and find a mean
ALTERNATIVE:
- Repeat steps 1-6 for five different angles, plot sin i against sin r and draw a line of best fit through the origin.
- Find the gradient of the line, this equals the refractive index
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.
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°
critical angle of prism is 42°
Therefore TIR occurs
If incident angle = 45°, then reflected angle= 45°
Therefore light is bent a total of 90°
What type of wave is a sound wave?
Longitudinal
Medium oscillates (to and fro) parallel to direction of wave travel
If reflection is light bouncing, what is refraction?
Refraction is light bending (changing direction)
Define the angle of refraction
the angle between the refracted ray and the normal
A prism is a triangular block of glass. The sides of the prism are not parallel.
When white light is shone through the prism, different wavelengths of light are deviated by different amounts.
What is observed and what is the effect called?
The white light splits into a range of colours called a spectrum.
The effect is called dispersion
Note: This shows that white light is a mixture of colours of the rainbow
Label the wavelength of the sound wave below
distance from middle of one compression to the middle of the adjacent compression.
compression to compression
Why does the light totally internally reflect down the glass tube?
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 dense medium?
Light speeds up, the waves spread out and the wavelength increases, the waves bend away from the normal
How can sound be produced?
Sound is a vibration. A vibrating object will produce sound.
Sound transfers energy without transferring matter. Matter oscillates (is disturbed) as the wave passes through it.
How is sound and visible light similar?
sound and light are waves
sound and light transfer energy without transferring matter
sound and light dissipate as they travel outward
sound and light can reflect, refract and diffract
List some properties of visible light
- is a form of radiation
- travels in straight lines
- transfers energy without transferring matter
- travels through a vacuum
- travels as waves at 300 000 000 m/s
- varies in frequency (red light lowest frequency, violet light highest frequency)
- it can refect, refract and diffract
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 dense medium
- rows of soldiers bunch up when in the mud, wavelength of light decreases when light enters more 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 dense medium
When white light is passed through a prism, which colour of light is deviated the least?
red
What is meant by monochromatic light?
Light of a single wavelength or colour.
When white light is passed through a prism, which colour is deviated the most?
violet
Define the angle of incidence
angle of incidence is the angle between the incident ray and the normal
What is the unit for wavelength of a sound?
metres (m)
In terms of TIR, what is the critical case?
When light is shining from a more dense medium to a less dense medium at exactly the critical angle.
In this case the light will run along the boundary with a refracted angle of 90°
What is a normal line?
A dotted line drawn 90° to mirror or boundary surface
State the law of reflection
incident angle = reflected angle
( note: the incident ray, normal line and reflected ray are all in the same plane)
What is the critical angle?
The critical angle is the largest angle of incidence for which refraction can still occur.
What happens to the speed, direction and wavelength of light when it enters a more dense medium at angle of 0° (along normal)?
Light slows down, the waves bunch up and the wavelength decreases but the direction does not change
