Session Ending Exam, 2021-22
Class-XII
Subject –Physics (042)
Max. Marks 35 Max. Time 2 Hrs
General Instructions:
(i) There are 12 questions in all. All questions are compulsory.
(ii) This question paper has three sections: Section A, Section B and Section C.
(iii) Section A contains three questions of two marks each,
Section B contains eight questions of three marks each,
Section C contains one case study-based question of five marks.
(iv) There is no overall choice. However, an internal choice has been provided in one question of two marks and two questions of three marks. You have to attempt only one of the choices in such questions.
(v) You may use log tables if necessary but use of calculator is not allowed.
SECTION – A
1. The current in the forward bias is known to be more (~mA) than the current in the reverse bias (~ mA). What is the reason, then, to operate the photodiode in reverse bias?
2. Calculate the orbital period of the electron in the first excited state of hydrogen atom.
OR
Define ionization energy. How would the ionization energy change when electron in hydrogen atom is replaced by a particle of mass 200 times that of the electron but having the same charge?
3. The circuit shown in the figure has two oppositely connected ideal diodes connected in parallel. Find the current flowing through each diode in the circuit.
SECTION – B
4. Draw the circuit diagram of a half wave rectifier and explain its working. Also, give the input and output waveforms.
5. The following graph shows the variation of photocurrent for a photosensitive metal:
(a) Identify the variable X on the horizontal axis.
(b) What does the point A on the horizontal axis represent?
(c) Draw this graph for three different values of frequencies of incident radiation υ1, υ2 and υ3 (υ1 > υ2 > υ3) for same intensity.
(d) Draw this graph for three different values of intensities of incident radiation I1, I2 and I3 (I1 > I2 > I3) having same frequency.
6. Using Bohr’s postulates, obtain the expression for the total energy of the electron in the stationary states of the hydrogen atom. Hence draw the energy level diagram showing how the line spectra corresponding to Balmer series occur due to transition between energy levels.
7. (a) How is the size of a nucleus experimentally determined? Write the relation between the radius and mass number of the nucleus. Show that the density of nucleus is independent of its mass number.
(b) The nuclear radius of 27Al13 is 3.6 fermi. Find the nuclear radius of 64Cu29.
8. Two wavelengths of sodium light 590 nm and 596 nm are used, in turn to study the diffraction taking place at a single slit of aperture 2 × 10–4 m. The distance between the slit and the screen is 1.5 m. Calculate the separation between the positions of the first maxima of the diffraction pattern obtained in the two cases.
9. A person can see clearly objects only when they lie between 50 cm and 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, person has to use what type and power of the correcting lens?
OR
In Young’s double experiment, a monochromatic light of wavelength 5400 Å produces a fringe width of 3 mm. If this source is replaced by another source of monochromatic light of wavelength 6300 Å, then find the fringe width.
10. An object placed at a distance of 16 cm from a convex lens produces an image of magnification m(m > 1). If the object is moved towards the lens by 8 cm then again an image of magnification m is obtained. What is the numerical value of the focal length of the lens?
11. A double convex lens is made of a glass of refractive index 1.55, with both faces of the same radius of curvature. Find the radius of curvature required, if the focal length is 20 cm.
OR
In a single slit diffraction experiment, the width of the slit is reduced to half its original width. How would this affect the size and intensity of the central maximum?
(a) If width of slit is reduced to half then the size of central maxima will become double.
(b) If width of slit is reduced to half its original width then the intensity of central maximum will be one-fourth.
SECTION – C
12. CASE STUDY : SPEED OF AN ELECTROMAGNETIC WAVE
