Lenses

A student determine the focal length of a device ‘X’ by focusing the image of a distant object on a screen placed 20 cm from the device on the same side as the object. The device ‘X’ is

• concave lens of focal length 10 cm

• convex lens of focal length 20 cm

• concave mirror of focal length 10 cm

• concave mirror of focal length 20 cm

In which of the following, the image of an object placed at infinity will be highly diminished and point sized?

• Concave mirror only

• Convex mirror only

• Convex lens only

• Concave mirror, convex mirror, concave lens and convex lens

Which of the following ray diagrams is correct for the ray of light incident on a lens shown in Fig. 10.7?

• Figure A

• Figure B

• Figure C

• Figure D

If the magnification of a lens has negative value, the image is:

A) virtual B) real C) inverted D) erect

1. 
   

• Both A & C

• Both B & D

• Both A & D

• Both B & C

Express the power of a concave lens of focal length 20cm with its sign.

1. 
   

• 5 D

• -0.5 D

• -5 D

• 0.5 D

If an object of size 5 cm is placed 20 cm from a lens and its image of same size is formed 20 cm from lens on other side, lens is :

1. 
   

• Convex

• Concave

• Prism

• Glass Slab

A lens of power 6 D is put in contact with a lens of power -4 D. The combination will behave like a:

• 1. Divergent lens of focal length 25 cm

• 1. Convergent lens of focal length 50 cm

• 1. Divergent lens of focal length 20 cm

  
  

• 1. Convergent lens of focal length 100 cm

  
  

If image formed by a lens is always diminished and between F and O then the lens is:

• 1. Concave

• Convex

• Both A and B

• 1. None of these

A spherical mirror and a thin spherical lens have each a focal length -15 cm. The mirror and the lens are likely to be

• the mirror is concave and the lens is convex

• both concave

• the mirror is convex but the lens is concave

• both convex.

An object is placed 25 cm away from a convex lens of focal length 20 cm. Where will the image be formed?

• Same side as the object

• Between 20 cm and 40 cm on the other side of the lens

• At a distance more than 40 cm on the other side of the lens

• At 40 cm on the other side of the lens