Question

A thin convex lens made from crown glass $$\left( {\mu = \frac{3}{2}} \right)$$  has focal length $$f.$$ When it is measured in two different liquids having refractive indices $$\frac{4}{3}$$ and $$\frac{5}{3}$$ it has the focal lengths $${f_1}$$ and $${f_1}$$ respectively. The correct relation between the focal lengths is:

A. $${f_1} = {f_2} < f$$
B. $${f_1} < f$$   and $${f_2}$$ becomes negative  
C. $${f_2} < f$$   and $${f_1}$$ becomes negative
D. $${f_1}$$ and $${f_2}$$ both become negative
Answer :   $${f_1} < f$$   and $${f_2}$$ becomes negative
Solution :
By Lens maker's formula for convex lens
$$\eqalign{ & \frac{1}{f} = \left( {\frac{\mu }{{{\mu _L}}} - 1} \right)\left( {\frac{2}{R}} \right) \cr & {\text{for, }}{\mu _{{L_1}}} = \frac{4}{3},{f_1} = 4R \cr & {\text{for, }}{\mu _{{L_2}}} = \frac{5}{3},{f_2} = - 5R \cr & \Rightarrow \,\,{f_2} = \left( - \right)ve \cr} $$

Releted MCQ Question on
Optics and Wave >> Ray Optics

Releted Question 1

When a ray of light enters a glass slab from air,

A. Its wavelength decreases.
B. Its wavelength increases.
C. Its frequency decreases.
D. neither its wavelength nor its frequency changes.
Releted Question 2

A glass prism of refractive index 1.5 is immersed in water (refractive index $$\frac{4}{3}$$ ). A light beam incident normally on the face $$AB$$  is totally reflected to reach on the face $$BC$$  if
Ray Optics mcq question image

A. $$\sin \theta \geqslant \frac{8}{9}$$
B. $$\frac{2}{3} < \sin \theta < \frac{8}{9}$$
C. $$\sin \theta \leqslant \frac{2}{3}$$
D. None of these
Releted Question 3

A ray of light from a denser medium strike a rarer medium at an angle of incidence $$i$$ (see Fig). The reflected and retracted rays make an angle of $${{{90}^ \circ }}$$ with each other. The angles of reflection and refraction are $$r$$ and $$r’$$ The critical angle is
Ray Optics mcq question image

A. $${\sin ^{ - 1}}\left( {\tan r} \right)$$
B. $${\sin ^{ - 1}}\left( {\tan i} \right)$$
C. $${\sin ^{ - 1}}\left( {\tan r'} \right)$$
D. $${\tan ^{ - 1}}\left( {\sin i} \right)$$
Releted Question 4

A ray of light from a denser medium strike a rarer medium at an angle of incidence $$i$$ (see Fig). The reflected and retracted rays make an angle of $${{{90}^ \circ }}$$ with each other. The angles of reflection and refraction are $$r$$ and $$r’$$ The critical angle is
Ray Optics mcq question image

A. $${\sin ^{ - 1}}\left( {\tan r} \right)$$
B. $${\sin ^{ - 1}}\left( {\tan i} \right)$$
C. $${\sin ^{ - 1}}\left( {\tan r'} \right)$$
D. $${\tan ^{ - 1}}\left( {\sin i} \right)$$

Practice More Releted MCQ Question on
Ray Optics


Practice More MCQ Question on Physics Section