Sample Question Paper for class 12th Physics (Annual Examination)

 Sample Question Paper for class 12th 

Physics (Annual Examination)

PRE BOARD EXAMINATION 2021-22

SUBJECT- PHYSICS

Class – XII

Time: 3Hours                                                                             Max. Marks: 70

 

GERNRAL INSTRUCATION: -

1.     All the questions are compulsory.

2.     There are 5 sections sec. A, Sec. B, Sec. C, Sec. D, and Sec. E.

3.     Section A has 14 questions  each 1 mark.

4.     Section B has 2 case based questions 4 marks each. Section C contains 9 short answer questions 2 marks each. Section D has 5 questions 3 marks each. Section E has 3 long answers questions 5 marks each.

5.     There is no overall choice. However internal choice is provided. You have to attempt only 1 of choices in such questions.

Section – A

Q1.    What does the additive nature of electric charge mean?

Q2.    Name the physical quantity whose SI unit is volt, meter. Is it a scalar or a vector?

Q3.    If the plants of a charged capacitor be suddenly connected to each other by a wire, what will happen?

Q4.    Two wires of equal length, one of copper & the other of manganic have the same resistance. Which wire is thicker?

Q5.    Write the expression for the magnetic moment of a circutor coil of area A carrying a current I, in vector form.

Q.6    Can we decrease the range of an ammeter?

Q7.    What is the angle of dip at a place where the horizontal & vertical components of the earth’s magnetic field are equal?

Q8.    Two bar magnets arc quickly moved towards a metallic loop connected across a capacitor C as shown in figure. Predict the polarity of capacitor.

Q9.    The peak value of emf in ac is E₀.

          Write its.

(i)                rms

(ii)             average value over a complete cycle.

Q10.  A green light is incident from water to the air water interface at the eritical angle (0). Which part of the spectrum will come out in the air medium?

Q11. What is the ration of the fringe width for bright & dark fringes in young’s double slit experiment.

Q12.  Plot a graph showing the variation of photoelectric current with collector plate, potential at a given frequency but for two different intensities I₁ and I₂ (I₂ + I₁).

Q.13  What is the shortest wave length present in the paschal series of spectral times.

Q14.  Write the expression for Bohr’s radius in Hydrogen atom.

 

Section – B

Q15.  A mercury arc lamp provides 0.10W of  UV radiation at a V wavelength of 253.7nm, all other wave lengths have been absorbed by filters. The radiation of all on a photoelectric device (a photo tube) at a distance of 1m. The cathode of photo tube consists of effective area of 4cm². According to classical theory, the radiation from the arc lamp spreads out uniformly in space as a spherical wave. The radius of potassium atom is 0.2nm & the photo conversion efficiency of the photo-tube is 5% which implies that each photon has probability of 0.0e of effecting an electron from the cathode [hc = 1242 ev nm]. With the help of the comprehension,

Choose the most appropriate answer-

I    Time of exposure to radiation required by the potassium atom to eject a photoelectron is:

a)       300 sec.

b)      200 sec.

c)       355 sec.

d)      980 sec.

II       The photo electric current is:

a)       20n A

b)     10 m A

c)       30 µ A

d)      32.5 nA

III      The cut off potential is:

a)       3 V

b)      1.78 V

c)       2.67 V

d)      4.38 V

Q16.  In a mixture of H^- , He⁺ gas (He+ is singly ionized He atom), H atom & He+ ions are excited to their respective first excited states. Subsequently, H atom transfer their total excitation energy to He+ ions (by collisions). Assume that the Bohr’s model of atom is valid. With the help of comprehension, choose the most appropriate answer:

I        The quantum number n of the state finally populated in He+ ions is:

a)       2

b)      3

c)       4

d)      5

II The wavelength of light emitted in the visible region by He+ ions after collisions with H- atoms is:

a)       8.5  x 10^-7 m

b)      5.6  x 10^-7 m

c)       4.8  x 10^-7 m

d)      4.0  x 10^-7 m

III      The ratio of the kinetic energy of n = 2 electron for H- atom to that of  He+ ions is:

a)       ¼

b)       ½

c)       1

d)      2

 

Section – C

Q17. The fig. shows a uniformly charged non-conducting rod, what is the direction of electric field at “P” due to charge on rod?

OR

Name the electromagnetic radiation having the wavelength range from 1nm to 10^-3 nm. Give its two important applications.

Q18.  A regular hexagon of side 10cm has a change such at each of its verticls. Find the potential at the center.

Q19.  A 600PF capacitor is charged by a 200 V supply. It is then disconnected from the supply & is connected to another  uncharged 600 PF capacitor. How much electrostatic energy is lost in the process?

OR

A small telescope has an objective of focal length 144cm & an eyepiece of focal length 6,0 cm. What is the magnifying power of telescope? What is the tube length.

Q20.  Write the working principle of a parallel plate capacitor. On what foctors, the capacitance depends?

OR

Plot a graph showing temperature dependence of resistivitly for a typical semiconductor.

Q21.  Current flowing through a wire varies with time “t” in second as :

          1 = (2t + 4) A

          How much charge passes through a cross section of the wire in 2 sec.

Q22.  State henz’s law. Does it violate the principle of conservation f energy?

Q23.  Show that the current leads the voltage in phase by ℼ/2  in an ac circuit containing an ideal capacitor.

OR

An alternating voltage given by : V = 70 sin 100 ℼt is connected across a pure resistor of 25 n find:

(i)                The frequency of source.

(ii)             The rums current through the resistor.

Q24.  A point source “S” is place mid way between two concave mirrors having equal focal length “F” as shown. Find the value of “d” for which only one image is formed.

Q25.  For a glass prism (µ = √3) the angle of minimum deviation is equal to the angle of prism. Find the angle of prism.

Section – D

Q26.  Draw V-I characteristics of a p – n junction diode. Why is the current under the reverse bise almost Independent of the applied potential up to a critical voltage?

OR

Laser light of wavelength 630nm incident on a pair of slits produces an interference pattern in which the bright fringes are separated by 7.2 mm. Find the wavelength of another source of light which produces fringes separated by 8.1 mm using same pair of spits.

Q27.  Draw the circuit diagram of a full wave rectifier using p – n junction diode. Explain its working & show the output & input wave forms.

Q28.  Define power of a lens. Write its unit. Deduce the relation : 1/f = 1/f₂ + 1/f₃  for to thin lenses kept in contact coaxially.

Q29.  A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15cm. Give the location of image & the magnification.

OR

Obtain the resonant frequency of a series LCR circuit with L = 2, OH, C = 32 uf, R = 10Ω. What is the Q value of this circuit?

Q30.  In an ammeter (consisting of a Galvanometer) & a shunt, 0.5 % of main current passes through the galvanometer. The resistance of galvanometer is “G”. Find shunt in terms of “G”.

Section – E

Q31. 

I        In young’s soluble slit experiment, derive the condition for (i) constructive & (ii) destructive interference at a point on screen.

II       In YDSE the angular fringe width is 0.1⁰. The wavelength of light is 6000A, what is the spacing between slits?

OR

I        Explain giving reasons, the basic difference in converting a galvanometer into                (i)           a voltmeter           (ii)     an ammeter

II       Two along straight parallel conductor carrying steady currents 1 & 12 are separated by a distance “d”. Explain with the help of suitable diagram how the magnetic field acting between two? Mention the nature of force.

Q32.  The primary coil of an ideal step-up transformer has 100 turn & transfer motion ration is 100. The input voltage & power are 220 V & 1100 W. Find:

       I.            Number of turns in secondary.

    II.            Current in primary.

 III.            Voltage across secondary

IV.            Current in secondary

   V.            Power in secondary.

OR

Deduce the expression for the torque experienced by a rectangular loop carrying a steady current “1” & placed in a uniform magnetic field “B”. Indicate the direction of the torque acting on loop.

Q33.  Calculate the value of the current drawn from 5V battery in the circuit shown:

 

 

 

 

OR

A.   State, with the help of circuit diagram the working principle of a meter bridge. Obtain the expression used for determining the unknown resistance.

B.   What happens if the galvanometer & cell are interchanged at the balance point of the bridge?

C.   Why is it considered important to obtain the balcne point near the mid-point of wire?