(a) Define the term 'focal length of a mirror'. With the help of a ray diagram, obtain the relation between its focal length and radius of curvature.
(b) Calculate the angle of emergence (e) of the ray of light incident normally on the face AC of a glass prism ABC of refractive index √3. How will the angle of emergence change qualitatively, if the ray of light emerges from the prism into a liquid of refractive index 1.3 instead of air?
or
(a) Define the term 'resolving power of a telescope'. How will the resolving power be affected with the increase in
(i) Wavelength of light used.
(ii) Diameter of the objective lens.
Justify your answers.
(b) A screen is placed 80 cm from an object. The image of the object on the screen is formed by a convex lens placed between them at two different locations separated by a distance of 20 cm. Determine the focal length of the lens.
[2020 | Delhi | Section - D | SET - 1 SET - 2 SET - 3, Q.35 Q.36 Q.37]
(i) Wavelength of light used.
(ii) Diameter of the objective lens.
(b) A screen is placed 80 cm from an object. The image of the object on the screen is formed by a convex lens placed between them at two different locations separated by a distance of 20 cm. Determine the focal length of the lens.
[2020 | Delhi | Section - D | SET - 1 SET - 2 SET - 3, Q.35 Q.36 Q.37]
Solution :
a) —
b) Applying the Snell's Law at the interace AB
µ = sini/sine
1/√3=sin30°/sin e
sine=(1/2)×√3
sine=√3/2
sine=sin 60°
e=60°
When the prism is placed in air then the angle of emergence is 60°.
We know, when light travel from denser to rarer medium then it bends away from the normal. So, when the prism is placed in a liquid of refractive index 1.3 instead of air having refractive index of 1, then it will bend less. Hence, the angle of emergence will be less than 60° .
