A concave mirror has radius of curvature of 40 cm. It is at the bottom of a glass that has water filled up to 5 cm (see figure). If a small particle is floating on the surface of water, its image as seen, from directly above the glass, is at a distance d from the surface of water. The value of d is dose to: (Refractive index of water = 1.33)

Two moles of helium gas is mixed with three moles of hydrogen molecules (taken to be rigid). What is the molar specific heat of mixture at constant volume ? (R = 8.3 J/mol K)

A magnetic compass needle oscillates 30 times per minute at a place where the dip is 45^o, and 40 times per minute where the dip is 30^o. If B₁ and B₂ are respectively the total magnetic field due to the earth at the two places, then the ratio $${{{B_1}} \over {{B_2}}}$$ is best given by :

Which of the following combinations has the dimension of electrical resistance ($$ \in $$₀ is the permittivity of vacuum and $$\mu $$₀ is the permeability of vacuum)?