NEET Modern Physics MCQs & PYQs

All electron ejected from a surface by incident of wavelength 200 nm can be stopped before
travelling 1 meter in the direction of a uniform electric field of 4 NC–¹ the work function of the
surface is :

A 200 W sodium street lamp emits yellow light of wavelength 0.6 μm. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is :

When photons of energy hv fall on an aluminium plate (of work function E0), photoelectrons of maximum kinetic energy K are ejected. If the frequency of the radiation is doubled, the maximum kinetic energy of the ejected photoelectrons will be :

Binding energy per nucleon verses mass number curve for nuclei is shown in the figure. W, X, Y and Z are four nuclei indicated on the curve. The process that would release energy is :

Energy from the sun is received on the earth at the rate of 2 cal per cm² per min. If average wavelength of solar light be taken at 5500 Å, then how many photons are received on the earth per cm² per min ?

\[\left( h=6.6\times 10^{-34}J-s,cal = 4.2 J \right)\]

A photon and an electron have equal energy E. \[\lambda_{photon}/\lambda_{electron}\] is proportional to

Ultraviolet light of wavelength 300 nm and intensity 1.0 watt/m² falls on the surface of a photosensitive material. If 1% of the incident photons produce photoelectrons, then the number of photoelectrons emitted from an area of 1.0 cm² of the surface is nearly

Photoelectric emission is observed from a metallic surface for frequencies ν1 and ν2 of the incident light rays (ν1 > ν2). If the maximum value of kinetic energy of the photoelectrons emitted in the two cases are in the ratio of 1 : k, then the threshold frequency of the metallic surface is :

The figure shows the variation of photo current with anode potential for a photo-sensitive surface for three different radiations. Let Ia, Ib, and Ic be the intensities and fa, fb and fc be the frequencies for the curves a, b and c respectively :

Half life of a radio-active substance is 20 minutes. The time between 20% and 80% decay will be :