How many photons of wavelength 439 nm shuold strike on a perfectly reflecting surface in 1 second. So, that it may exert a force of 10 N.

A photon of wavelength 4 xx 10 ^(-7) m strickes on metal surface, the work function of the metal being 2.13 eV. Calculate the velocity of the photoelectron (1 eV = 1. 6020 xx 10 ^(-19) J)

A point source S emitting light of wavelength 600 nm is placed at a very small height h above a flat reflecting surface AB [Fig.6.07].The intensity of the reflected light is 36% of the incident intensity.Interfrerence fringes are observed on a screen placed parallel to the reflecting surface at a very large distance D from it. If the intensity t pint P corresponds to a maximum,calculate the minimum distance through which the reflecting surface AB sould be shifted so that the intensity at P again becomes maximum.

Consider a 20 W bulb emitting light of wavelength 5000 oversetcircA and shining on a metal surface kept at a distance 2m . Assume that the metal surface work function of 2eV and that each atom on the metal surface can be treated as a cirular disc of radius 1.5 A. How many photons would atomic disc receive within time duration calculated in (iii) above?

Consider a 20 W bulb emitting light of wavelength 5000 oversetcircA and shining on a metal surface kept at a distance 2m . Assume that the metal surface work function of 2eV and that each atom on the metal surface can be treated as a cirular disc of radius 1.5 A. Estimate no. of photons emitted by the bulb per second.[Assume no other losses]

A current balance is a device to measure magnetic forces. It is constructed from two parallel coils, each with an average radius of 12.5 cm. The lower coil rests on a balance, it has 20 turns and carries a constant current of 4.0 A. The upper coil, suspended 0.314 cm above the lower coil, has 50 turns and a current that can be varied. The reading of the balance changes as the. magnetic force on the lower coil changes. What current is needed in the upper coil to exert a force of 1.0 N on the bottom coil?

How many electrons should be removed from a coin of mass 1.6 g, so that it may float in an electric field of intensity 10^9NC^-1 directed upward.

Suppose we have a large number of identical particles, very small in size. Any two of them at 10 cm separation repel with a force of 3 x 10^-10N. Suppose you measure the repulsion and find it 6xx10^-6N . How many particles were there in the group?

The energy flux of sunlight reaching the surface of the earth is 1.388 xx 10^3 W/m^2 . How many photons per square metre are incident on the Earth per second? Assume that the photons in the sunlight have an average wavelength of 550 nm.

Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW. How many photons per second, on the average, arrive at a target irradiated by this beam? (Assume the beam to have uniform cross-section which is less than the taget area).