Refraction Part B,C and D Flashcards
What is a prism?
A prism is a transparent medium bounded by five plane surfaces with a triangular cross section.
True or False:
(i) Two refracting surfaces are parallel to each other
(ii) Emergent ray gets deviated towards the base of the prism
(i) False. They are not parallel to each other but are inclined on each other forming the angle of the prism A.
(ii) True.
How does the angle of incidence affect the angle of deviation?
It is observed that as the angle of incidence increases, the angle of deviation first decreases, reaches a minimum value for a certain angle of incidence and on further increasing angle of incidence, the angle of deviation begins to increase.
Define: Position of minimum deviation
It is the position of a prism with respect to the incident ray at which the incident ray suffers minimum deviation
Write the formulas of:
(i) Deviation
(ii) Minimum deviation
(iii) Angle of Prism
(i) deviation = (i1+i2)-(r1+r2) OR deviation = (i1+i2) - A
(ii) Min deviation = 2i - A
(iii) A = r1+r2
State any 2 factors affecting Angle of Deviation.
- Angle of Incidence
- Material of Prism
- Wavelength of light used
- Angle of Prism
How are angle of deviation and material of prism ( refractive index ) related?
Directly proportional, increase in refractive index results in increase in angle of deviation
How are the angle of deviation and wavelength related?
Inversely proportional, angle of deviation decreases with increase in wavelength
How are the angle of deviation and angle of prism related?
Directly proportional, increase in angle of prism results in increase of angle of prism
Write the formulas of:
(i) Refractive index of a medium w respect to air
(ii) Shift
(i) aμm = real depth / apparent depth
(ii) Shift = RD - AD OR
Shift = RD x (1-1/aμm)
State any 2 factors that shift depends upon and their relation with shift.
(i) R.I of medium. R.I increases, shift increases
(ii) Thickness of the denser medium. Thickness increases, shift increases
(ii) Wavelength of incident light. Wavelength increases, shift decreases.
What are the consequences of refraction of light? (4m)
easiest points acc to me
- A star appears to twinkle in the sky due to fluctuation of the refractive index of air due to changes in temp
- The print of paper is seen to be raised when a glass slab is placed over it
- The sun is seen a few minutes before it actually rises above the horizon in the morning and a few minutes after it actually sets in the evening
- A person’s legs appear to be short when seen from outside when they are standing in a swimming pool or a water tank.
Define: Critical Angle
Critical angle is the angle of incidence in the denser medium corresponding to which the angle of refraction in the rarer medium is 90 degrees
What is the relationship b/w critical angle and refractive index?
Sin C = 1/aμm
What are the two factors affecting the critical angle? How is it affected by them?
(i) Wavelength of light. C increases with increase in wavelength
(ii) Temperature. C increases with increase in temp.
What is total internal reflection?
When a ray of light travelling in a denser medium is incident at the surface of a rarer medium at an angle of incidence greater than the critical angle for the pair of media, the ray is totally reflected back into the denser medium. This phenomenon is called total internal reflection.
State the two essential conditions for total internal reflection
(i) Light must travel from a denser to rarer medium
(ii) Angle of incidence must be greater than the critical angle for the pair of media.
Where is total internal reflection used?
Construction of periscope, binoculars and certain times of cameras where a total internal reflecting prism replaces a plane mirror.
Difference between total internal reflection and reflection by a plane mirror (2m)
Total Internal Reflection
1. no loss of energy. Energy of the reflected ray is the same as that of the incident ray
2. Takes place only when light passes from denser to rarer at an angle of incidence greater than the C for the pair of media.
3. Entire light is reflected
Reflection by Plane Mirror
1. There is loss of energy. Energy of reflected ray is always lesser than that of the incident ray.
2. Takes place when light is incident on a plane mirror from any medium at any angle of incidence
3. Only a part of the light is reflected. Rest is refracted and absorbed
State the consequences of total internal reflection. (4m)
- A crack in a glass vessel often shines like a mirror
- A piece of diamond sparkles when viewed from certain directions
- An optical fibre is used to transmit a light signal over a long distance without any loss of energy
- On a hot sunny day a driver may see a pool of water or wet road in front of him at some distance. This phenomenon is called a mirage and is observed in a desert.
