Modern Physics Practice Level - 1 - Class 12 MCQ

Ultraviolet light of wavelength 300 nm and intensity 1.0 Wm^-2 falls on the surface of a photosensitive material. If one per cent of the incident photons produce photo-electrons, then the number of photoelectrons emitted per second from an area of 1.0 cm² of the surface is nearly
 

In a photocell, with excitation wavelengthl , the fastselectron has speed v. If the excitation wavelength ischanged to 3λ /4, the speed of the fastest electron will be

Two identical photocathodes receive light of frequenciesf₁and f₂. If the velocities of the photoelectrons (of massmi coming out are v₁ and v₂, respectively, then

The work function of a metal is W and λ is the wave length of the incident radiation. There is no emission of photoelectrons when

Monochromatic light incident on a metal surface emitselectrons with kinetic energies from zero to 2.6 eV.What is the least energy of the incident photon if thetightly bound electron needs 4.2 eV to remove?

The work function for sodium surface is 2.0 eV andthat for aluminium surface is 4.2 eV. The two metalsare illuminated with appropriate radiations so as tocause photoemission. Then

Representing the stopping potential V along y-axis and(1/ λ ) along x-axis for a given photocathode, the curveis a straight line, the slope of which is equal to

Electrons traveling at a velocity of 2.4 x 10⁶ ms^-1 entera region of crossed electric and magnetic fields shownin Fig. If the electric field is 3.0 x 10⁶ Vm and the fluxdensity of the magnetic field is 1.5 T, the electrons upon entering the region of the crossed fields will

A surface irradiated with light λ = 480 nm gives outelectrons with maximum velocity v m/s. the cin offwavelength being 600 nm. The same surface wouldrelease electrons with maximum velocity 2v m/s if it isirradiated by light of wavelength.

ln an experiment on the photoelectric effect, an evacuated photocell with a pure metal cathode is used. Which graph best represents the variation of V, the minimum potential difference needed to prevent current from flowing, when x. the frequency of the incident light, is varied ?
 

A metal surface in an evacuated tube is illuminated with monochromatic light causing the emission of photoelectrcss which are collected at an adjacent electrode. For a giwen intensity of light, the way in which the photocurrent I depends in the potential difference Vbetween the electrodes is shown by approximate graph in Fig. If the experiment were repeated with light of twice the intensity but the same wavelength, which of the graphs below would best represent the new relation between I and VI (In these graphs, the result of the original experiment is indicated by a broken line.)

If stopping potentials corresponding to wavelengths
respectively, then the work function of the 

The frequency and the intensity of a beam of light fallingon he surface of a photoelectric material are increasedby a factor of two. This will

The frequency of incident light falling on a photosensitivemetal plate is doubled, the KE of the emitted photoelectrons is

Lights of two different frequencies whose photons havey energies 1 and 2.5 eV, respectively, successivelyilluminate a metal whose work function is 0.5 eV. Theratio of the maximum speeds of the emitted electronswill be

A cesium photocell, with a steady potential differenceof 60 V across it, is illuminated by a small bright lightplaced 1 m away. When the same light is placed 2 maway, the electrons crossing the photocell

If 5% of the energy supplied to a bulb is irradiated asvisible light, how many quanta are emitted per secondby a 100 W lamp? Assume wavelength of visible lightas 5.6 x 10^-5 cm

Which of the following graphs correctly represents the variation of particle momentum with associated de Broglis wavelength ?

A point source causes photoelectric effect from a smallmetal plate. Which of the curves in Fig.may representthe saturation photo-current as a function of the distancebetween the source and the metal?

Let p and E denote the linear momentum and energy,respectively, of a photon. If the wavelength is decreased,

The human eye can barely detect a yellow light (λ = 6000 Å) delivers 1.7 x 10^-18 W to the retina. The number of photons per second falling on the eye is nearest to

An electron is accelerated through a potential differenceof 200 V. If e/m for the electron be 1.6 x 10¹¹coulomb kg^-1, then the velocity acquired by the electron will be

A photoelectric cell is connected to a source of variablepotential difference, connected across it and thephotoelectric current resulting (μA) is plotted againstthe applied potential difference (V). The graph in thebroken line represents one for a given frequency andintensity of the incident radiation. If the frequency isincreased and the intensity is reduced, which of thefollowing graphs of unbroken line represents the newsituation?

An electron of mass me and a proton of mass mp areaccelerated through the same potential difference. Theratio of the de Broglie wavelength associated with anelectron to that associated with proton is

A material particle with a rest mass mo is moving withvelocity of light c. Then, the wavelength of the de Brogliewave associated with it is

Out of a photon and an electron, the equation E = pc, is valid for

The ratio of momenta of an electron and an a -particlewhich are accelerated from rest by a potential differenceof 100 V is :