05 मार्च 2021




1.Electron volt is a unit of

(a) charge

(b) potential difference

(c) energy

(d) momentum

II.A uniform electric field is represented by a set of lines of force which are

(a) parallel

(b) converging

(c) diverging

(d) none of these

III. The length and area of cross section of metal wires are doubled, then change in its resistance

(a) no change

(b) half

(c) Four times

(d) doubled

IV. The instrument for the accurate measurement of EMF of a cell is:

(a) Voltmeter

(b) Ammeter

(c) Potentiometer

(d) Slide Wire Bridge

V.Which of the following in motion cannot be deflected by magnetic field?

(a) electron

(b) proton

(c) sodium lon

(d) neutron

VI. Magnetic field due to a current carrying conductor is zero:

(a) along a line perpendicular to the wire

(b) along a line in client 45° to the wire

(c) along the axial line of the wire

(d) it can never be zero

VII.A charged particle enters at 30° to the magnetic field, its path becomes:

(a) circular

(b) helical

(c) elliptical

(d) straight line

VIII. Induction furnace makes use of

(a) Self-induction

(b) Mutual-induction

(c) Eddy currents

(d) Magnetic flux

IX.A transformer works on the principle of

(a) Converter

(b) Inverter

(c) Eddy current

(d) Mutual induction

X.Consider the following type of electromagnetic radiations: radio waves, infrared, visible light.

Which of the following statements are correct?

(a) only radio waves can be used to transmit audio information

(b) only infrared radiation is emitted by very hot object

(c) only visible light can be detected by humans

(d) none of the above

XI.If 11 eV of energy is required to dissociate a carbon monoxide molecule into carbon and oxygen  atoms, then minimum frequency of the appropriate electromagnetic radiation to achieve the

dissociation lies in

(a) Visible region

(b) infra-red region

(c) ultra violet region

(d) microwave region

XII. Transmission of light in optical fiber is due to:

(a) scattering

(b) reflection

(c) refraction

(d) multiple total internal reflection

XIII.When a glass prism is placed inside water its dispersive power:

(a) Decreases

(b) increases

(c) remain the same

(d) may increase or decrease depending on the angle of prism

XIV. A beam of electrons is used in a Young's double slit experiment. The slit width is d. When the

velocity of electron is increased then:

(a) no interference is observed

(b) fringe width increases

(c) fringe width decrease

(d) fringe width remains same

XV.What happens, if monochromatic light used in Young's double slit experiment is replaced by white light:

(a) no fringes are observed 

(b) all bright fringes become white

(c) all bright fringes have colors between violet and red

(d) only the central fringe is white and all the other fringes are colored.

XVI.A telescope is focused on the moon. If a tiny drop of ink falls on its objective, then:

(a) moon will appear black

(b) field of view will be dark

(c) there will be a dark spot in the field of view

(d) brightness of the image will be slightly reduced

XVII.If the focal length of objective lens is increased, then the magnifying power of:

(a) microscope will increase but that of telescope decrease

(b) microscope and telescope both will increase

(c) microscope and telescope both will decrease

(d) microscope will decrease but that of telescope will increase

XVIII. The curve drawn between velocity and frequency of a photon in vacuum will be:

(a) straight line parallel to frequency axis

(b) a straight line parallel to velocity axis

(c) straight line passing through the origin and making an angle of 45° with frequency axis

(d) hyperbola

XIX.The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of the hydrogen atom


(a) 2:1

(b) 1:1

(c) 1:1

(d) 1:2

XX.An electric field is applied to a semiconductor. Let the number of charge carriers be n and the average drift velocity be v. If the temperature is increased:

(a) both n and v will decrease

(b) both n and v will increase

(c) n will increase but v will decrease

(d) v will increase but n will decrease

XXI.The conduction band in a solid is partially filled at 0 K. the solid sample is:

(a) conductor

(b) semiconductor

(c) insulator

(d) none of these

XXII.Two elementary particles which have almost infinite life time are

(a) Electron and neutron

(b) neutron and proton

(c) electron and proton

(d) none of the above

XXIII. The energy band gap is maximum in

(a) metals

(b) Superconductors

(c) insulators

(d) semiconductors

XXIV.An electron microscope is based upon de-Broglie hypothesis. (True/False)

XXV.The part of electromagnetic spectrum having the largest penetrating power is X-ray. (True/False)

XXVI.We cannot get diffraction pattern from a wide slit illuminated by monochromatic light.(True/False)

XXVII.Static charge produces electric field as well as magnetic field.


XXVIII.We can increase the range of a given ammeter.



2. When a dielectric slab is introduced between the plates of a charged capacitor with battery connected across the plates, what will happen to

(1) potential (ii) charge (iii) electric field

(iv) total energy


Capacitance of the capacitor is given by-C=        εΑ/d

i) After the introduction of dielectric slab, capacitance becomes,

  C=    ΚεΑ


 where, K is dielctric constant.


Capacitance increases as K>1 always.

ii) Charge is given by Q=CV

As C increases, Q also increases.

iii) Potential difference V is constant when,

battery remains connected.

iv) Electric field is given by      E=  Q

                                                          Κε Α

Therefore, E reduces by a factor of 1/K.

v) Energy stored in the capacitor is given by

E= 1/2CV2


2. A 500C charge is at the centre of square of side 10cm. Find work done in moving a charge of 10 C between two diagonally opposite points on the square.

3. Connecting wires are made up of copper.why?

ANSWER: Copper is the preferred metal for electrical wires as it has high electrical conductivity ; it's inexpensive; it's ductile. 


3. When a wire carries a current of 1.20 A, the drift velocity is 1.20 10-4 m/s. What is the drift velocity when the current is 6.00 A?

4. An electron beam moving with uniform velocity is gradually diverging. When it is accelerated to a very high velocity, it again starts converging. Why?

5. Name the physical quantity which is the ratio of magnetic flux and induced current? Define its SI units.

Answer : Ratio of magnetic flux and induced current is called Inductance or coefficient of self Induction. 

It's SI unit is HENRY. 

6. Which segment of EM waves lie near the high frequency end of visible part of EM spectrum?Give its one use. In what way this component of light has harmful effect on humans? (1/2, 1/2,1)

Answer: Ultra-Violet waves. These waves are used to kill bacteria.  Ultra-Violet waves can cause skin cancer. 

7. Photoelectric effect cannot be explained on the basis of wave nature of light. Why?


1. According to wave theory, after the light falls on a substance electrons are emitted after a small instant of time. However, in photoelectric effect, the electron emissions are immediate without a time delay.

2. The energy of a wave increases with increase in intensity. However, in photoelectric  effect, increase in intensity has no effect on the energy of electrons emitted. All that happens is the number of electrons emitted, increases.


7. The work function of a photosensitive material is 6.2 eV. The wavelength of the incident radiation for which stopping potential is 5V lies in which region.

8. What are the limitations of Rutherford's atomic model?

Answer: It is failed to explain the stability of the atom. It is failed to explain the complex spectrum 


9. Discuss the principle of potentiometer. Explain how will you compare EMF of two primary cells using a potentiometer?

Ans. A potentiometer works on the principle that potential difference across any part of a uniform wire is directly proportional to the length of that part of the wire when a constant current flows through the wire.

Potentiometer uses null method i.e., no current is drawn by the galvanometer from the cell in the balanced condition of the potentiometer. Therefore it measures true e.m.f. of the cell. To compare  e.m.f. of two cells, make the connections of shown in the following figure. Close the key K and note the deflection in Ammeter, keep this deflection constant till the end of experiment. Close the keys 1 and 3 and find the balance point say A. Note the length of wire OA = l1. Now, close the keys 2 and 3 and find the balance point B till the galvanometer gives no

deflection. Note OB = l2 


E1     l1

E2     l2

10. How can a galvanometer be converted into a voltmeter? Explain.

Ans : To convert a galvanometer into voltmeter a high resistance is connected in series with the Galvanometer.


G = resistance of the galvanometer 

Ig = the current which produces full scale deflection in the


R = high resistance connected in series with the galvanometer

V=  p.d. to be measured by the voltmeter.

Ohm's law, we get

Ig =V/R+G

IgR + IgG = V

 R = V- IgG/Ig

R= V/Ig - G


10. Long wire carries a steady Current I. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. Then it is bent into a circular coil of n turns. Find the magnetic field at the centre of the coil in the second case.

11. What do you understand by mutual induction? Derive an expression for the mutual inductance of two long coaxial solenoids having different radii and different number of turns.

Ans. Mutual induction. The phenomenon of producing current in a coil (or circuit) 

changing current in a neighbouring coil (or circuit) is called mutual induction.

Magnetic flux associated with second coil $€I, where I is the current in first coil

$ = MI

M is called coefficient of mutual induction.


I = 1, then $ = M

Thus coefficient of mutual induction between two coils is numerically equal to the magnetic flux associated with one coil when unit current is passed through the other.


11. A Transformer has an efficiency of 80%. It works at 4 kW and 100 V. If the secondary voltage is

240 V. Find the primary and secondary currents.

12. What do you mean by coherent sources of light? Write two conditions for two sources of light to be coherent.


Coherent sources of light are those which emit continuous light waves of same frequency, same wavelength and having either same phase or constant phase difference.

The following conditions are necessary to obtain coherent sources of light :

(i) The two sources should give monochromatic light i.e., light of single wavelength

(ii) The path difference between light waves from two sources should be small

(iii) The coherent sources of light should be obtained from a single source so that the phas dfference between the two waves remains constant with time.

12. In Young's experiment, two slits are 0.2 mm apart. The interference fringes for light of

wavelength 6000A are formed on the screen 80 cm away. Find

(a) How far is the second bright fringe from the central image?

(b) How far is the third dark fringe the central fringe?

13. State the basic postulates of Bohr's theory of atomic model. Obtain an expression for radius of the orbit of electron.

Ans. According to Bohr :

An atom consists of a small, positively charged massive core called nucleus, around which electrons revolve. The centripetal force required for their rotation is provided by force of attractrons between the nucleus and electrons.

The orbiting electrons existed in orbits that had discrete quantized energies.

i) When an electron makes a jump, from one orbit to another, the energy difference is carried off by a single photon of light which has energy equal to the energy difference between the two orbits.

If E, and E2 are the energies associated with two permitted orbits, then the frequency v of the emitted or absorbed photon is given by

E2 - E1,

= hv

1) The permitted orbits, in which electron can revolve, depend on quantized values of orbital angular momentum L, according to equation

L = nh/2Pi

When n 1, 2, 3, is called principal quantum number and h is planck's constant. The lowest value of n is 1. 

14. Using the necessary circuit diagram show how the V-I characteristics of a p-n junction are obtained in (i) forward biasing and (ii) reverse biasing.


15. Prove Gauss's law in electrostatics. Using Gauss's theorem, derive an expression for electric field intensity at a point due to an infinite plane sheet of charge.


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