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Physics · 2022 · 3 marks
CBSE 2022 · Region 3 · Set 1 · Q8
(a) Write two necessary conditions for total internal reflection. (b) Two prisms ABC and DBC are arranged as shown in figure. The critical angles for…
(a)
Write two necessary conditions for total internal reflection.
(b)
Two prisms ABC and DBC are arranged as shown in figure.
The critical angles for the two prisms with respect to air are $\displaystyle 41.1$° and $\displaystyle 45$° respectively. Trace the path of the ray through the combination.
(a)
An object is placed in front of a converging lens. Obtain the conditions under which the magnification produced by the lens is (i) negative and
(ii)
positive.
(b)
A point object is placed at O in front of a glass sphere as shown in figure. Show the formation of image by the sphere.
Marking-scheme solution
a) Two conditions
(i) The light must travel from an optically denser medium to a rarer medium.
(ii) Angle of incidence should be greater than the critical angle.
b)
(a) Two conditions $\displaystyle m=\frac{h^{\prime}}{h}=\frac{v}{u}$
(i) For real images / when object is placed beyond F, As $\displaystyle u$ is negative and $\displaystyle v$ is positive..
(ii) for virtual image / when object is kept between $\displaystyle F$ and the optical centre of the lens. As $\displaystyle u$ and $\displaystyle v$ both are negative.
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CBSE Class 12 Physics past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.