## PHYSICS (Theory)

General Instructions :
(i) All questions are compulsory. There are 26 questions in all.
(ii) This question paper has five sections : Section A, Section B, Section C, Section D and Section E.
(iii) Section A contains five questions of one mark each, Section B contains five questions of two markseach, Section C contains twelve questions of three marks each, Section D contains one value based question of four marks and Section E contains three questions of five marks each.
(iv) There is no overall choice. However, an internal choice has been provided in one question of two marks, one question of three marks and all the three questions of five marks weightage. You have to attempt only one of the choices in such questions.

### SECTION – A

Q1.An electron is accelerated through a potential difference V. Write the expression for its final speed, if it was initially at rest.

Q2.Two protons of equal kinetic energies enter a region of uniform magnetic field. The first proton enters normal to the field direction while the second enters at 30 degree to the field direction. Name the trajectories followed by them.

Q3.Draw a graph showing the intensity distribution of fringes due to diffraction at single slit.

Q4.Write the range of frequencies of electromagnetic waves which propagate through sky wave mode.

Q5.Define the power of a lens. Write its S.I. unit.

### SECTION – B

Q6.A rectangular frame of wire is placed in a uniform magnetic field directed outwards,normal to the paper. AB is connected to a spring which is stretched to AB and then released at time t = 0. Explain qualitatively how induced e.m.f. in the coil would vary
with time. (Neglect damping of oscillations of spring) Q7.(a) Define the term magnetic susceptibility and write its relation in terms of relative
magnetic permeability.
(b) Two magnetic materials A and B have relative magnetic permeabilities of 0.96 and 500. Identify the magnetic materials A and B.

Q8.(a) Give one use of electromagnetic radiations obtained in nuclear disintegrations.
(b) Give one example each to illustrate the situation where there is (i) displacement current but no conduction current and (ii) only conduction current but no displacement current.

Q9.Find the frequency of light which ejects electrons from a metal surface, fully stopped by a retarding potential of 3.3 V. If photo electric emission begins in this metal at a frequency of 8 × 1014 Hz, calculate the work function (in eV) for this metal.
OR
Monochromatic light of frequency 6.0 × 10^14 Hz is produced by a laser. The power emitted is 2.0 × 10–3 W. Calculate the

(i) energy of a photon in the light beam and
(ii) number of photons emitted on an average by the source.

Q10. Calculate the ratio of the frequencies of the radiation emitted due to transition of the electron in a hydrogen atom from its (i) second permitted energy level to the first level and (ii) highest permitted energy level to the second permitted level

### SECTION – C

Q11. Define electric flux and write its SI unit. The electric field components in the figure shown are : Ex= x, Ey= 0, Ez
= 0 where  =100 NCm . Calculate the charge within thecube, assuming a = 0.1m.

OR An electron falls through a distance of 1.5 cm in a uniform electric field of magnitude 2.0 × 104 N/C (Fig. a) Calculate the time it takes to fall through this distance starting from rest. If the direction of the field is reversed (fig. b) keeping its magnitude unchanged,calculate the time taken by a proton to fall through this distance starting from rest.

Q12. Two cells of emfs 1 &  2 and internal resistances r1 & r2 respectively are connected in parallel. Obtain expressions for the equivalent. (i) resistance and (ii) emf of the combination.

Q13.(a) Define SI unit of current in terms of the force between two parallel current carrying conductors.

(b) Two long straight parallel conductors carrying steady currents Ia and Ib along the same direction are separated by a distance d. How does one explain the force of attraction between them ? If a third conductor carrying a current Ic in the opposite direction is placed just in the middle of these conductors, find the resultant force acting on the third conductor.

Q14.(a) When an unpolarized light of intensity Io is passed through a polaroid, what is the intensity of the linearly polarized light ? Does it depend on the orientation of the polaroid ? Explain your answer.
(b) A plane polarized beam of light is passed through a polaroid. Show graphicallythe variation of the intensity of the transmitted light with angle of rotation of the polaroid in complete one rotation.

Q15.State Einstein’s photoelectric equation explaining the symbols used.Light of frequency  incident is on a photosensitive surface. A graph of the square of the maximum speed of the electrons ( ) v 2 max vs.  is obtained as shown in the figure.Using Einstein’s photoelectric equation, obtain expressions for (i) Planck’s constant
(ii) work function of the given photosensitive material in terms of parameters l, n and
mass of the electron m. Q16.(a) Draw a plot showing the variation of potential energy of a pair of nucleons as a
function of their separation. Mark the regions where the nuclear force is
(i) attractive and (ii) repulsive.
(b) In the nuclear reaction
Determine the values of a and b. Q17.(a) Write the truth table for the combination of the gates shown in the figure.

(b) Explain briefly how a photo diode operates. Q18.Draw a labelled circuit diagram of n-p-n germanium transistor in common emitterconfiguration. Explain briefly, how this transistor is used as a voltage amplifier.

Q19.(a) With the help of a ray diagram, show how a concave mirror is used to obtain an erect and magnified image of an object.
(b) Using the above ray diagram, obtain the mirror formula and the expression for linear magnification.

Q20.(a) State Biot – Savart law and express it in the vector form.
(b) Using Biot – Savart law, obtain the expression for the magnetic field due to a circular coil of radius r, carrying a current I at a point on its axis distant x from the centre of the coil.

Q21.Using Kirchhoff’s rules, calculate the potential difference between B and D in the circuit diagram as shown in the figure. Q22.(i) Write two points to distinguish between interference and diffraction fringes.
(ii) In a Young’s double slit experiment, fringes are obtained on a screen placed a certain distance away from the slits. If the screen is moved by 5 cm towards the slits, the fringe width changes by 30 m. Given that the slits are 1 mm apart, calculate the wavelength of the light used.

### SECTION – D

Q23.Mrs. Rajlakshmi had a sudden fall and was thereafter unable to stand straight. She was in great pain. Her daughter Rita took her to the doctor. The doctor took a photograph of Mrs. Rajlakshmi’s bones and found that she had suffered a fracture. He advised her
to rest and take the required treatment.
(a) Name the electromagnetic radiation used to take the photograph of the bones.
(b) How is this radiation produced ?
(c) Mention the range of the wavelength of this electromagnetic radiation.
(d) Write two values displayed by Rita.

### SECTION – E

Q24.Two point charges q and –q are located at points (0, 0, –a) and (0, 0, a) respectively.
(a) Find the electrostatic potential at (0, 0, z) and (x, y, 0)
(b) How much work is done in moving a small test charge from the point (5, 0, 0) to (–7, 0, 0) along the x-axis ?
(c) How would your answer change if the path of the test charge between the same points is not along the x-axis but along any other random path ?
(d) If the above point charges are now placed in the same positions in a uniform external electric field E, what would be the potential energy of the charge system in its orientation of unstable equilibrium ?
OR
A capacitor of capacitance C1 is charged to a potential V1 while another capacitor of capacitance C2 is charged to a potential difference V2. The capacitors are now disconnected from their respective charging batteries and connected in parallel to each
other.
(a) Find the total energy stored in the two capacitors before they are connected.
(b) Find the total energy stored in the parallel combination of the two capacitors.
(c) Explain the reason for the difference of energy in parallel combination in comparison to the total energy before they are connected.

Q25.(a) Draw graphs showing the variations of inductive reactance and capacitive reactance with frequency of the applied ac source.
(b) Draw the phasor diagram for a series RC circuit connected to an ac source.
(c) An alternating voltage of 220 V is applied across a device X, a current of 0.25 A flows, which lag behind the applied voltage in phase by 2 radian. If the same voltage is applied across another device Y, the same current flows but now it is in phase with the applied voltage.
(i) Name the devices X and Y.
(ii) Calculate the current flowing in the circuit when the same voltage is applied across the series combination of X and Y.
OR
(a) State the principle of working of a transformer.
(b) Define efficiency of a transformer.
(c) State any two factors that reduce the efficiency of a transformer.
(d) Calculate the current drawn by the primary of a 90% efficient transformer which steps down 220 V to 22 V, if the output resistance is 440 .

Q26.(a) Explain with the help of suitable diagram, the two processes which occur during the formations of a p-n junction diode. Hence define the terms (i) depletion region and (ii) potential barrier.
(b) Draw a circuit diagram of a p-n junction diode under forward bias and explain its working.
OR
(a) Describe briefly three factors which justify the need for modulation of audio
frequency signals over long distances in communication.
(b) Draw the waveforms of (i) carrier wave, (ii) a modulating signal and (iii) amplitude modulated wave.