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: 


Correct option is


Since the sun is very distant, u is very large and so (1/u) is practically zero. So   


i.e., the image of sun will be formed at the focus and will be real, inverted and diminished.

Now as the rays from the sun subtend an angle θ radians at the pole, hence according to figure, we have   


(where d = diameter of the image of the sun)    




A transparent cube of 15 cm edge contains a small air bubble. Its apparent depth when viewed through one face is 6 cm and when viewed through the opposite face is 4 cm. Then the refractive index of the material of the cube is:   


Time taken by sunlight to pass through a window of thickness 4 mm whose refractive index is 1.5 is: 


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


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: 


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:    


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: 


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: 


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:


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:


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: