Board Paper of Class 12 Physics Term-II 2022 Delhi(SET 3) - Solutions

(i) Define SI unit of  power of a lens.
(ii) A plano convex lens is made of glass of refractive index 1.5. The radius of curvature of the convex surface is 25 cm.

OR

A slit of width 0.6 mm is illuminated by a beam of light consisting of two wavelengths 600 nm and 480 nm. The diffraction pattern is observed on a screen 1.0 m from the slit. Find:
(i) The distance of the second bright fringe from the central maximum pertaining to light of 600 nm.
(ii) The least distance from the central maximum at which bright fringes due to both the wavelengths coincide. VIEW SOLUTION

An electron in a hydrogen atom makes transitions from orbits of higher energies to orbits of lower energies.
(i) When will such transitions result in (a) Lyman (b) Balmer series?
(ii) Find the ratio of the longest wavelength in Lyman series to the shortest wavelength in Balmer series. VIEW SOLUTION

With the help of a ray diagram, show how a compound microscope forms a magnified image of a tiny object, at least distance of distinct vision. Hence derive an expression for the magnification produced by it. VIEW SOLUTION

(a) Give an example each of a metal from which photoelectric emission takes place when irradiated by (i) UV light (ii) visible light.
(b) The work function of a metal is 4.50 eV. Find the frequency of light to be used to eject electrons from the metal surface with a maximum kinetic energy of 6.06 × 10^–19 J. VIEW SOLUTION

In a fission event of ${}_{92}{}^{238}\mathrm{U}$ by fast moving neutrons, no neutrons are emitted and final products, after the beta decay of the primary fragments, are ${}_{58}{}^{140}\mathrm{Ce}$ and ${}_{44}{}^{99}\mathrm{Ru}$. Calculate Q for this process. Neglect the masses of electrons/positrons emitted during the intermediate steps.

Given : $\mathrm{m}\left({}_{92}{}^{238}\mathrm{U}\right)=238.05079\mathrm{u}; \mathrm{m}\left({}_{58}{}^{140}\mathrm{Ce}\right)=139.90543\mathrm{u}$
            
             $\mathrm{m}\left({}_{44}{}^{99}\mathrm{Ru}\right)=98.90594\mathrm{u}; \mathrm{m}\left({}_0{}^1\mathrm{n}\right)=1.008665\mathrm{u}$ VIEW SOLUTION

(i) Arrange the following electromagnetic radiation in the ascending order of their frequencies:
          X-rays, microwaves, gamma rays, radio waves
(ii) Write two uses of any two of these radiation.

OR

With the help of a ray diagram explain the working of a reflecting telescope. Mention two advantages of a reflecting telescope over a refracting telescope. VIEW SOLUTION

A ray of light passes through a prism of refractive index $\sqrt{2}$ as shown in the figure. Find:

(i) The angle of incidence (∠r₂) at face AC.
(ii) The angle of minimum deviation for this prism. VIEW SOLUTION

(i) Draw V-I characteristics of a p-n Junction diode.
(ii) Differentiate between the threshold voltage and the breakdown voltage for a diode.
(iii) Write the property of a junction diode which makes it suitable for rectification of ac voltages. VIEW SOLUTION

A ray of light travels from a denser to a rarer medium. After refraction, it bends away from the normal. When we keep increasing the angle of incidence, the angle of refraction also increases till the refracted ray grazes along the interface of two media. The angle of incidence for which it happens is called critical angle. If the angle of incidence is increased further the ray will not emerge and it will be reflected back in the denser medium. This phenomenon is called total internal reflection of light.

(i) A ray of light travels from a medium into water at an angle of incidence of 18°.
(ii) A point source of light is placed at the bottom of a tank filled with water, of refractive index µ, to a depth d. The area of the surface of water through which light from the source can emerge, is:
(iii) For which of the following media, with respect to air, the value of critical angle is maximum?
(iv) The critical angle for a pair of two media A and B of refractive indices 2.0 and 1.0 respectively is:
(v) The critical angle of pair of a medium and air is 30°. The speed of light in the medium is: VIEW SOLUTION