Question

23 and 24 could you check my answers

The speed of laserlight in a transparent solid is 0.49 c. What is the critical angle of a beam of light ray at the interface between the transparent solid and a vacuum? 26 degree 23 degree 21 degree 29 degree Lots of people think they can see better, and read easier in bright light than in dim light. Is this belief true? Yes, because bright light increases the magnification provided by the cornea and crystalline lens. Yes, because bright light tends to reduce astigmatism due to excess contraction of the ciliary mu Scles. Yes, this is true because contraction of the pupil in bright light simulates a pinhole camera and minimizes spherical aberration. No, because contraction of the pupil in bright light means the same amount of light strikes the retina, and hence the nature of the image formed is unchanged. No, this is a purely psychological effect, since the optical properties of the eye are not dependent on the light used. Bright light merely stimulates some visual neurons that are normally dormant.

Answer 1

Q.23) Speed of light in the solid = 0.49c and Speed of light in vacuum = c

where c = 3 x 10⁸ m/s

So the refractive index of the solid will be: n = c/v = c/0.49c = 2.0408

Now for Critical Angle, the incident medium is the solid and the refractive medium is the vacuum.

And the relation between the indices of refraction and the critical angle is given by:

$\small sin\theta_c = \frac{n_r}{n_i}$

=> $\small \theta_c = sin^{-1}(\frac{n_r}{n_i}) = sin^{-1}(\frac{1}{2.0408}) = 29.34\degree \approx 29\degree$

Q.24) True. Our pupils (black hole in the eye) get dilated when in dark to absorb as much light (hence as much information of the surrounding) as we can. If the surrounding is well lit then our pupils contract and make a fine pinhole. This reduces the aberrations since only the paraxial rays (light rays making small angle with the optic axis) are reaching your eyes which will effectively describe the image accurately.