what is the imp questions of ray optics for cbse board
Answers
Answer:
Question
Aglasslensof refractive index 1.5 is placed in a trough of liquid. What must be the refractive index of the liquid in order to mark the lens disappear? (Delhi 2008)
Answer:
In order to make the lens disappear the refractive index of liquid must be equal to 1.5 i.e. equal to that of glass lens.
Question
How does the angle of minimum deviation of a glass prism vary, if the incident violet light is replaced with red light? (All India 2008)
Answer:
We know that λ red > λ violet, therefore µ red < µ violet and hence δ red < δ violet.
When incident violet light is replaced with red light, the angle of minimum deviation of a glass decreases.
Question
Why does the bluish colour predominate in a clear sky? (All India 2008)
Answer:
Blue colour of the sky : The scattering of light by the atmosphere is a colour dependent. According to Rayleigh’s law, the intensity of scattered light I∝1λ4, blue light is scattered much more strongly than red light. Therefore, the colour of sky becomes blue. The blue component of light is proportionately more in the light coming from different parts of the sky. This gives the impression of the blue sky.
Question .
A glass lens of refractive index 1.45 disappears when immersed in a liquid. What is the value of refractive index of the liquid? (Delhi 2010)
Answer:
The value of refractive index of the liquid should be 1.45 so that the glass lens of refractive index 1.45 disappears when immersed in a liquid.
Question
State the conditions for the phenomenon of total internal reflection to occur. (Delhi 2010)
Answer:
Two essential conditions for total internal reflection are :
Light should travel from an optically denser medium to an optically rarer medium.
The angle of incidence in the denser medium must be greater than the critical angle for the two media.
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