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).

The principle of 'parallax' is used in the determination of distance of nearby stars. The role of distant object O there is now taken by nearby distant stars. The baseline AB is the line joining the Earth's two locations six months apart in its orbit around the Sun. That is the baseline is about the disameter of the earth's orbit = 3 xx 10^11 m. However, even the nearest stars are so distant that with such a long baseline theyshow parallax only of the order 1 s of arc or so. A parsec is a convenient unit of length on the astronomical sxale. It is the distance of an object that will show a parallar of 1s of arc from opposite ends of a baseline equal to the distance from the Earth to the Sum How much is a parsec in terms of metre?

Assume that earth has a charge of surface density 1 electron per metre^3 . Calculate the earth's electric field

In a photoelectric effect set up, a point source of light of power 3.2 xx10^(-3) W emits monoenergetic photons of energy 5eV.The source is located at a distance of a stationary metallic sphere of work function 3eV and radius 8xx10^(-3)m .The efficiency of photoelectron emission is one for every 10^(6) incident photons.Assume that the sphere is isolated and initially neutral and the photoelectrons are initially swept away after emission. Calculate the number of photoelectrons emitted per second.

A photon of wavelength 4 xx 10 ^(-7) m strickes on metal surface, the work function of the metal being 2.13 eV. Calculate energy of the photon (eV)

In a photoelectric effect set up, a point source of light of power 3.2 xx10^(-3) W emits monoenergetic photons of energy 5eV.The source is located at a distance of a stationary metallic sphere of work function 3eV and radius 8xx10^(-3)m .The efficiency of photoelectron emission is one for every 10^(6) incident photons.Assume that the sphere is isolated and initially neutral and the photoelectrons are initially swept away after emission. Find the ratio of the wavelength of incident light to the de Broglie wavelength of the fastest phtotelectrons emitted.

According to Stefan's law of radiation, a black body radiates energy sigmaT^4 from its unit surface area every second where T is the surface temperature of the black body and sigma = 5.67 xx 10^-8 W//m^2 K^4 is known as Stefan's constant. A nuclear weapon may be thought of as a ball of radius 0.5 m. When detonated, it reaches temperature of 10^6 K and can be treated as a black body. Estimate the power it radiates

Assume that earth has a charge of surface density 1 electron per metre^2 . Calculate the earth's electric potential just outside the earth's surface.

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 kinetic energy of the emission