Two identical thin plano-convex glass lenses
(refractive index 1.5) each having radius of
curvature of 20 cm are placed with their convex
surfaces in contact at the centre. The intervening
space is filled with oil of refractive index 1.7. The
focal length of the combination is :-

A mass m moves in a circle on a smooth horizontal
plane with velocity v0 at a radius R0. The mass is
attached to a string which passes through a smooth
hole in the plane as shown.

The tension in the string is increased gradually and
finally m moves in a circle of radius  R₀/2.The final
value of the kinetic energy is :-

A radiation of energy ‘E’ falls normally on a perfectly
reflecting surface. The momentum transferred to
the surface is (C = Velocity of light) :-

A certain metallic surface is illuminated with
monochromatic light of wavelength, l. The stopping
potential for photo-electric current for this light is
3V₀. if the same surface is illuminated with light of
wavelength 2λ, the stopping potential is V0. The
threshold wavelength for this surface for photoelectric
effect is :-

A Carnot engine, having an efficiency of n = 1/10 as
heat engine, is used as a refrigerator. If the work
done on the system is 10 J, the amount of energy
absorbed from the reservoir at lower temperature is 

Which logic gate is represented by the following
combination of logic gates ?