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12 Question Paper


I PERIODICAL TEST 2022-23

CLASS: XII                        SUBJECT: PHYSICS

Time Allowed: 90 min                                       Maximum Marks: 50

Instructions: All questions are compulsory. This question paper consists of 25 questions. 

  • Qn 1 to Qn 10 are MCQs of 1 mark each, 

  • Qn 11 to Qn 18 are of short answer type, carrying 2 marks each. 

  • Qn 19 to Qn 23 are of short answer type, carrying 3 marks each. 

  • Qn 24 is a Case Based Question of 4 marks

  • Qn 25 is of long answer type, carrying 5 marks

Section A


A 12pF capacitor is connected to a 50V battery. The electrostatic energy stored in the capacitor is (in Joule)

A.     15x10-9                B.     6 x10-8                         C.      3x10-8                  D.    3x10-9 

1

The S.I. unit of electric field intensity is 

  1. Nm/C

  2. J/C

  3. C/m

  4. N/C

1

Name the physical quantity whose S.I. unit is J/C 

  1. Electric density

  2. Dipole moment 

  3. Electric field

  4. Electric potential difference

1

A wire of resistivity ρ is stretched to double its length. Its new resistivity would be

  1. ρ

  2. 2ρ

  3. 4ρ

  4. 6ρ

1

Due to rise of temperature, the drift velocity of electrons in conductors

  1. Increase

  2. Decrease

  3. No effect

  4. first increase then decrease linearly

1

Graph showing the variation of current versus voltage for a material gallium arsenide is shown in the figure. Choose the correct option:

  1. In region AB the resistance is negative

  2. In region BC the resistance is negative

  3. In region BC ohm's law is obeyed

  4. All are correct.

1

The I-V graph for two identical conductors of different materials A and B is shown in the figure. Which one of the two has higher resistivity?

  1. Wire A

  2. Wire B

  3. Both wires have same resistivity

  4. Data insufficient

1

Select the correct option

  1. Electric current is a vector quantity

  2. Current density is a scalar quantity

  3. Electric current is a scalar quantity

  4. None of these

1

The magnitude of the drift velocity per unit electric field is called

  1. Electric current

  2. Current density

  3. Electrical conductivity

  4. Mobility

1

The potential difference between the terminals of a cell when no current is passing through the cell is known as

  1. Electrodes of cell

  2. Potential difference

  3. Electromotive force

  4. Potential energy

Section B

1

Write S.I. unit of electrical resistivity. How does the electrical resistivity of metals vary with increase of temperature?

2

Define electric flux. A point charge causes an electric flux of –1.0 × 103 Nm2/C to pass through a spherical Gaussian surface of 10.0 cm radius centered on the charge.  If the radius of the Gaussian surface were doubled, how much flux would  pass through the surface?

2

Draw the electric field lines due to a point charge Q when (i) Q>0 and (ii) Q<0.

2

Two charges 3 × 10–8 C and –2 × 10–8 C are located 15 cm apart. At what point on the line joining the two charges, is the electric potential zero? Take the potential at infinity to be zero.

2

Find the equivalent capacitance of the network between points A and B shown in figure

2

Find an expression for torque experienced by the electric dipole kept in a uniform electric field.

2

Define current density and internal resistance of an electric cell.

2

State Ohm’s law. Draw VI- characteristics of a non linear circuit.

Section C

2

Define drift velocity and find its relation with electric current.

3

Find expression for the potential energy of an electric dipole kept in a uniform electric field? Hence find the work done to rotate it from its stable to unstable equilibrium.

OR 

Define electric potential at a point and derive an expression for it.

3

State Gauss's theorem in electrostatics. Use Gauss's theorem in electrostatics to derive an expression for the electric field intensity at a point due to an infinitely long, thin, uniformly charged straight wire.

OR State Gauss's theorem in electrostatics. Use Gauss's theorem in electrostatics to derive an expression for the electric field intensity at a point near a uniformly charged infinite thin plane sheet.

3

The plate area of a parallel plate capacitor is A and separation between plates is d. Find an expression for its capacitance.

3

Calculate the potential at a point P due to a charge of 4 × 10–7C located 9 cm away. (b) Hence obtain the work done in bringing a charge of 2 × 10–9 C from infinity to the point P. 

3

Section D

Case Based Question


A conductor has free electrons. As long as the electric field is not zero, the free charge carriers would experience force and drift. In the static situation, therefore, E should have no tangential component. A neutral conductor has equal amounts of positive and negative charges in every small volume or surface element. When the conductor is charged, the excess charge can reside only on the surface in the static situation. In a system of conductors of arbitrary size, shape and charge configuration, each conductor is characterized by a constant value of potential, but this constant may differ from one conductor to the other. If the conductor is charged or charges are induced on a neutral conductor by an external field, all charges reside only on the outer surface of a conductor with cavity.

based on the above facts, answer these question:

(i) an equipotential surface is that which has

A.  zero potential at each point                     B. constant potential at each point  

C. electric field lines tangential to it               D none of these

(ii) the electric field at the surface of a charged conductor having surface charge density σ is

A.  σ.ε                   B.   2σ.ε                        C. σ/ε                      D. σ/2ε

(iii) Whatever be the charge and field configuration outside, any cavity in a conductor remains shielded from outside electric influence, the field inside the cavity is always

A.  zero at each point                     B. constant at each point  

C. infinity          D none of these

(iv) Statement 1: At the surface of a charged conductor, the electrostatic field must be tangential to the surface at every point.

Statement 2:  Electrostatic potential is constant throughout the volume of the conductor and has the same value (as inside) on its surface. 

A.  Statement 1 as well as Statement 2, both are true                    

B. Statement 1 true while Statement 2 is false  

C. Statement 1 false  while Statement 2 is true         

D. none of these

Section E

Long Answer Question

4

Find an expression for the electric field strength at any point on the axial line of an electric dipole

OR 

Find an expression for the electric field strength at any point on the equatorial line of an electric dipole.

2018 19 Time 90 min M 50


State Ampere’s circuital law.

1


Write expression for the Lorentz force on a charge.

1


Why should the electrostatic field be zero inside a conductor?

1


Define ‘intensity of magnetisation’ of a magnetic material. How does it vary with temperature of a paramagnetic material?

2


Name material, one in each case, suitable for  (i) making a permanent magnet (ii) core of electric transformer

2


State coulomb’s law for the force between two point charges.

How would the force change if the dielectric constant of the medium in which the charges are kept, increases?

2


(a) What is the least possible charge?

(b) Explain why two field lines never cross each other at any point?

2


Two point charges qA = 3 μC and qB = –3 μC are located 20 cm apart in vacuum.

(a) What is the electric field at the midpoint O of the line AB joining the two charges?

(b) If a negative test charge of magnitude 1.5 × 10–9 C is placed at this point, what is the force experienced by the test charge?

3


State Gauss’s law for electrostatics. Use it to prove that the electric field at a point due to a uniformly charged infinite plane sheet is independent of the distance of the point from the sheet.

3


An electric dipole is kept in a uniform electric field. Show that the net force acting on it is zero.

Calculate the change in its potential energy when rotated from angle 0° to 180° with respect to the field.

3


Write any two characteristics of equipotential surface.

Depict  equipotential surfaces for a system of two identical positive point charges placed at a separation d.

3


Obtain the equivalent capacitance of the network in Fig. 2.35. For a 300 V supply, determine the charge and voltage across the capacitor C4.

3


Derive expression for the force between two long parallel current carrying conductors.

3


Write the value of angle of dip at the magnetic equator of the Earth.

A magnetic needle free to rotate in a vertical plane parallel to magnetic meridian has its north tip down 60° with the horizontal. The horizontal component of the Earth’ magnetic field at the place is known to be 0.4 G. determine the magnitude of Earth’s magnetic field at the place.

Not in syllabus of 2022 23

3


Deduce the expression for the magnetic dipole moment of electron orbiting around the nucleus of hydrogen atom. Not in syllabus of 2022 23

OR

An electron moves around nucleus of Hydrogen atom of radius 0.5 A° with a speed of 200 km/s. calculate:

  1. orbital current due to electron

  2. the magnetic moment associated with the electron

3


  1. Not in syllabus of 2022 23 In a meter bridge the null point is obtained 40 cm from end A. when a resistance of 10 ohm is connected in series with R, null point shifts by 10 cm. find the values of R and S

  1. In the circuit assume point A to be at zero potential, use Kirchhoff’s rule to determine potential at the point B.

5


Not in syllabus of 2022 23

Write the principle of working of potentiometer. Describe briefly using circuit diagram, how it is used to : compare the emfs of two cells OR to find the internal resistance of a cell.

5


Not in syllabus of 2022 23

Draw a schematic diagram of a cyclotron. Write its principle. What are the uses of electric and magnetic fields in it? Show that cyclotron frequency is independent of energy of particle.

OR

With the help of labeled diagram state the principle and working of a moving coil galvanometer. Show that current is proportional to the deflection.

5


SESSION 2018-19

           CLASS XII                                       SUBJECT: PHYSICS

MARKING SCHEME




MARKS


Statement of Ampere’s circuital law.

1


Lorentz force on a charge F=qvxB

1


Reason for the electrostatic field be zero inside a conductor

1


Definition of ‘intensity of magnetisation’ of a magnetic material. 

it decreases with rise of temperature of a paramagnetic material.

1+1


(i) carbon steel (ii) soft iron

1+1


Statement of coulomb’s law for the force between two point charges.

The force decreases

1+1


(a) e = charge on electron or proton

(b) it would give two directions of the field

1+1


(a) 5.4 x 106 N/C along OB

(b) 8.1 × 10–3   along OA

3/2 +3/2++


Statement of Gauss’s law for electrostatics. 

Proof that the electric field at a point due to a uniformly charged infinite plane sheet is independent of the distance of the point from the sheet.

1

2


Showing that the net force acting on it is zero.

change in its potential energy when rotated from angle 0° to 180° with respect to the field +2pE

1

2


any two characteristics of equipotential surface.

equipotential surfaces for a system of two identical positive point charges placed at a separation d.

2


1


equivalent capacitance of the network 200/3 pF

the charge and voltage across the capacitor C4.

20 nC 200 V

1

1

1


Derivation of expression for the force between two long parallel current carrying conductors.

3


the value of angle of dip at the magnetic equator of the Earth = 90 degree

calculation of the magnitude of Earth’s magnetic field at the place.

1

2


Derivation of the expression for the magnetic dipole moment of electron orbiting around the nucleus of hydrogen atom.

OR

For calculation of

  1. orbital current due to electron

  2. the magnetic moment associated with the electron

3


Or

2

1


  1. the values of R =20 ohm and S = 30 ohm

  2. potential at the point B = 2 V

3

2


principle of working of potentiometer. 

circuit diagram

use to : compare the emfs of two cells OR to find the internal resistance of a cell.

1

1

3


schematic diagram of a cyclotron

principle.

uses of electric and magnetic fields in it

cyclotron frequency is independent of energy of particle.

OR

labeled diagram

principle

working of a moving coil galvanometer

current is proportional to the deflection.

1

1

1+1

1

Or

1

1

2

1

CLASS XII

PHYSICS THEORY TERM II

SESSION 2021 - 22

MM : 35                                                        TIME : 2 Hours

General Instructions:

There are 12 questions in all. All questions are compulsory.

This question paper has three sections: Section A, Section B and Section C.

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.

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.

You may use log tables if necessary but use of calculator is not allowed.

SECTION A

Q1.    Give an example of doping in a pure semiconductor to make n type semiconductor. Draw the energy band diagram of n type semiconductor.

Q2.    If the frequency of incident radiation increases above threshold value, how does this change: 

(a) photoelectric current 

(b) stopping potential? 

           OR

            Use Bohr's  model of hydrogen atom to calculate the speed of electron in the ground state.

Q3.    How is a photodiode connected in a circuit? Plot I-V characteristics of a photodiode for different intensities of light.

SECTION B

Q4.    Calculate the shortest wavelength in the Balmer series of hydrogen atom. In which region (IR, visible or UV) of the hydrogen spectrum does this wavelength lie?

Q5.    Give a circuit diagram of a full wave rectifier using a pn junction diode and explain its working. Give its input and output waveforms.

Q6.    (a) two nuclei have mass numbers in the ratio 1 : 8, what is the ratio of their nuclear radii? 

(b) Draw a plot of potential energy of a pair of nucleons as a function of their separation and write any two characteristic properties  of nuclear force.

Q7.    Define wavefront. Draw the shape of a refracted wavefront when the plane incident wave undergoes refraction from one medium to another. Hence, prove Snell’s law of refraction.

Q8.

  1. Draw a ray diagram of a compound microscope for the final image formed at the least distance of distinct vision?

  2. Write the formula for its magnifying power and explain why both the objective and eyepiece of a compound microscope must have short focal lengths.

OR

  1. Draw a ray diagram of an Astronomical Telescope for the final image formed at infinity.

  2. A small telescope has an objective lens of focal length 140 cm and an eyepiece of focal length 5.0 cm. Find the magnifying power of the telescope for viewing distant objects when the telescope is in normal adjustment,

  3. What is the separation between the objective and eye lens when the final image is formed at infinity?

Q9. 

  1. Light of wavelength 2000 Å falls on a metal surface of work function 4.2 eV. What is the kinetic energy (in eV) of the fastest electrons emitted from the surface? (h = 6.4 x 10-34 Js, e = 1.6 x 10-19 C)

  2. An electron is revolving around the nucleus with a constant speed of 2.5 x 108 m/s. Find the de Broglie wavelength associated with it. mass of electron in kg = 9.1 x 10-31

Q10.    Derive lens maker's formula for thin lenses.

Q11

  1. Name the part of the electromagnetic spectrum whose wavelength lies in the range 10-10 m. Give its one use.   

  2. Name the e.m. waves which are suitable for radar systems used in aircraft navigation. Write the range of frequency of these waves.

  3. If the Earth did not have an atmosphere, would its average surface temperature be higher or lower than what it is now? Explain.

OR

  1. "If the slits in Young's double slit experiment are identical, then intensity at any point on the screen may vary between zero and four times the intensity due to single slit". Derive a relevant mathematical expression for maximum and minimum intensity for interference of two waves.

  2. Draw the intensity distribution as a function of the angular position of fringes when diffraction of light takes place through a coherently illuminated single slit.

SECTION C

Q12.    CASE STUDY: Optical fibres: Now-a-days optical fibres are extensively used for transmitting audio and video signals through long distances. Optical fibres are fabricated with high quality composite glass/quartz fibres. Each fibre consists of a core and cladding. The refractive index of the material of the core and cladding is slightly different. When a signal in the form of light is directed at one end of the fibre at a suitable angle, it comes out at the other end. There is no appreciable loss in the intensity of the light signal. Optical fibres are fabricated such that light reflected at one side of the inner surface strikes the other at an angle larger than the critical angle ic. Even if the fibre is bent, light can easily travel along its length. Thus, an optical fibre can be used to act as an optical pipe.

(a) Which of the following phenomena is used as the principle of working of optical fibres?

(i) Refraction, Total internal Reflection

(ii) Dispersion and Refraction

(iii) Dispersion and scattering of light

(iv) Total internal Reflection and diffraction.

(b) If n is the refractive index of the denser medium with respect to the rarer medium then 1/n = ? 

      (i) sin–1 ic              (ii)    tan–1 ic          (iii)  sec–1 ic             (iv) 90°

(c) In an optical fiber, if n1 and n2 are the refractive indices of the core and cladding, then which among the following, would be correct?

     (i) n1 < n2          (ii) n1 = n2       (iii) n1 << n2       (iv) n1 > n2

(d) For total internal reflection, a ray of light must travel from

(i) optically denser to optically rarer medium

(ii) optically rarer to optically denser medium

(iii) only in denser medium

(iv) none of these

(e) At critical angle of incidence, the refraction angle r is

(i) 0 < r< 90°      (ii) r = 90°       (iii) 0 < r< 45°          (iv) r > 90°

Solution hint

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