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