The equivalent focal length of the two lenses in contact is 80 cm . If the focal length of one of the lenses is 20 cm. The power of the second lens is :

A. 1.66 D
B. 3.75 D
C. - 3.75 D
D. - 1.66 D


If the critical angle for total internal reflection from a medium to vacuum is `30^circ` the velocity of light in the medium is

A. 3 x `10^8` m/s
B. 1.5x `10^8` m/s
C. 6 x `10^8` m/s
D. 2.4 x `10^8` m/s


The angle of prism is `6^circ` and its refractive index for green light is 1.5. For a green ray passes through it the deviation  will be :

A. `30^circ`
B. `25^circ`
C. `12^circ`
D. `3^circ`


Two plane mirrors are inclined at an angle of` 45^circ` to each other . If an object is placed in between them , the number of images formed is :

A. 4
B. 5
C. 6
D. 7


Find the change in internal energy of the system when a system absorbs 2 kcal of heat and at the same time does 500 J of work :

A. 7900 J
B. 8200 J
C. 5600 J
D. 6400 J