68. An astronomical telescope has a length of 44 cm and tenfold magnification. The focal length of the objective lens is ?

32. The focal length of converging lens is measured for violet, green and red colours. It is respectively $f_v, f_g, f_r$. We will get ?

14. An electromagnetic radiation of frequency n, wavelength λ, travelling with velocity v in air enters in a glass slab of refractive index (μ). The frequency, wavelength and velocity of light in the glass slab will be respectively ?

A parallel plate condenser with oil between the plates (dielectric constant of oil K = 2 ) has a capacitance C. If the oil is removed, then capacitance of the capacitor becomes ?

From a point charge, there is a fixed point A. At A, there is an electric field of 500 V/m and potential difference of 3000 V. Distance between point charge and A will be ?