Question

Diameter of a plano-convex lens is 6 cm and thickness at the centre is 3 mm. If the speed of light in the material of the lens is , the focal length of the lens is:  

Solution

Correct option is

30 cm

 

  

   

As the lens is plano-convex, i.e., R1 = R and R2 = ∞,   

  

As speed of light in the medium of lens is   

                  

 From figure,   

                

  

SIMILAR QUESTIONS

Q1

A ray of light is incident on the surface of separation of a medium with the velocity of light at an angle 45o and is refracted in the medium at an angle 30o. What will be the velocity of light in the medium

Q2

A ray of light falls on a transparent glass slab with refractive index (relative to air) of 1.62. The angle of incidence for which the reflected and refracted rays are mutually perpendicular is: 

Q3

A concave mirror of focal length f produces an image n times the size of the object. If the image is real, then the distance of the object from the mirror is:    

Q4

A convex mirror of focal length f produces an image (1/n)th of the size of the object. The distance of the object from the mirror is: 

Q5

A short linear object of length L lies on the axis of a spherical mirror of focal length f at a distance u from the mirror. Its image has an axial lengthL’ equal to: 

Q6

A thin convergent glass lens (μg = 1.5) has a power of +5.0 D. When this lens is immersed in a liquid of refractive index  it acts as a divergent lens of focal length 100 cm. The value of μl must be:

Q7

The sun (diameter = D) subtends an angle of θ radians at the pole of a concave mirror of focal length f. The diameter of the image of the sun formed by the mirror is: 

Q8

A double convex lens of focal length 6 cm is made of glass of refractive index 1.5. The radius of curvature of one surface is double that of the other surface. The value of smaller radius of curvature is:

Q9

A luminous point is moving at speed v0 towards a spherical mirror, along its axis. Then the speed at which the image of this point object is moving is given by (with R = radius of curvature and u = object distance):  

Q10

A slide projector gives a magnification of 10. If it projects a slide of dimensions 3 cm × 2 cm on a screen, the area of the image on the screen will be: