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CBSE Class 12 Board Exam Physics Paper 2018 2019 2020 With Solutions

Here we are providing CBSE Previous Year Question Papers Class 6 to 12 solved with soutions CBSE Class 12 Board Exam Physics Paper 2018 2019 2020 with Solutions Physics sample paper class 12, Physics previous year question paper class 12, cbse class 12 Physics sample paper, cbse class 12 Physics sample paper 2020, Physics sample paper class 12 2020, cbse sample paper 2020 class 12 Physics, class 12 Physics s Practice of previous year question papers and sample papers protects each and every student to score bad marks in exams.If any student of CBSE Board continuously practices last year question paper student will easily score high marks in tests. Fortunately earlier year question papers can assist the understudies with scoring great in the tests. Unraveling previous year question paper class 12 Physics is significant for understudies who will show up for Class 12 Board tests.

Class 12 Subject Physics Paper Set 1 with Solutions

SECTION A

Note : Select the most appropriate option from those given below each question :


Question 1: (Marks 1)

If the net electric flux through a closed surface is zero, then we can infer

(A) no net charge is enclosed by the surface.

(B) uniform electric field exists within the surface.

(C) electric potential varies from point to point inside the surface.

(D) charge is present inside the surface.


Answer :

(A) no net charge is enclosed by the surface


Question 2: (Marks 1)

An electric dipole consisting of charges + q and – q separated by a distance L is in stable equilibrium in a uniform electric field  E . The electrostatic potential energy of the dipole is

(A) qLE

(B) zero

(C) – qLE

(D) – 2 qEL


Answer :

(C) −qLE


Question 3: (Marks 1)

A potentiometer can measure emf of a cell because

(A) the sensitivity of potentiometer is large.

(B) no current is drawn from the cell at balance.

(C) no current flows in the wire of potentiometer at balance.

(D) internal resistance of cell is neglected.


Answer :

(C) No current flows in the potentiometer wire at balance


Question 4: (Marks 1)

Two resistors R1 and R2 of 4 Ω and 6 Ω are connected in parallel across a battery. The ratio of power dissipated in them, P1 : P2 will be

(A) 4 : 9

(B) 3 : 2

(C) 9 : 4

(D) 2 : 3


Answer :

(B) 3:2


Question 5: (Marks 1)

The magnetic dipole moment of a current carrying coil does not depend upon

(A) number of turns of the coil.

(B) cross-sectional area of the coil.

(C) current flowing in the coil.

(D) material of the turns of the coil.


Answer :

(D) material of the turns of the coil


Question 6: (Marks 1)

Larger aperture of objective lens in an astronomical telescope

(A) increases the resolving power of telescope.

(B) decreases the brightness of the image.

(C) increases the size of the image.

(D) decreases the length of the telescope.


Answer :

(A) increases the resolving power of telescope


Question 7: (Marks 1)

A biconvex lens of glass having refractive index 1·47 is immersed in a liquid. It becomes invisible and behaves as a plane glass plate. The refractive index of the liquid is

(A) 1·47

(B) 1·62

(C) 1·33

(D) 1·51


Answer :

(A) 1.47


Question 8: (Marks 1)

For a glass prism, the angle of minimum deviation will be smallest for the light of

(A) red colour.

(B) blue colour.

(C) yellow colour.

(D) green colour.


Answer :

(A) red colour


Question 9: (Marks 1)

Which of the following statements is not correct according to Rutherford model ?

(A) Most of the space inside an atom is empty.

(B) The electrons revolve around the nucleus under the influence of coulomb force acting on them.

(C) Most part of the mass of the atom and its positive charge are concentrated at its centre.

(D) The stability of atom was established by the model.


Answer :

(D) The stability of atom was established by the model


Question 10: (Marks 1)

Photons of energies 1 eV and 2 eV are successively incident on a metallic surface of work function 0·5 eV. The ratio of kinetic energy of most energetic photoelectrons in the two cases will be

(A) 1 : 2

(B) 1 : 1

(C) 1 : 3

(D) 1 : 4


Answer :

(C) 1:3

Note : Fill in the blanks with appropriate answer :

Question 11: (Marks 1)

The magnetic field and angle of dip at a place on the earth are 0·3 G and 30, respectively. The value of vertical component of the earth’s magnetic field at the place is ___________ .


Answer :

0.15G


Question 12: (Marks 1)

Laminated iron sheets are used to minimize ___________ currents in the core of a transformer.


Answer :

Eddy


Question 13: (Marks 1)

The number of turns of a solenoid are doubled without changing its length and area of cross-section. The self-inductance of the solenoid will become ___________ times.


Answer :

Four times


Question 14: (Marks 1)

According to Bohr’s atomic model, the circumference of the electron orbit is always an ___________ multiple of de Broglie wavelength.

OR

In -decay, the parent and daughter nuclei have the same number of _____________ .


Answer :

Integral

OR

Nucleons


Question 15: (Marks 1)

A ray of light on passing through an equilateral glass prism, suffers a minimum deviation equal to the angle of the prism. The value of refractive index of the material of the prism is ___________ .


Answer :

√3

Note : Answer the following :

Question 16: (Marks 1)

Write the mathematical form of Ampere-Maxwell circuital law.


Answer :

Write the mathematical form of Ampere-Maxwell circuital law


Question 17: (Marks 1)

How does an increase in doping concentration affect the width of depletion layer of a p-n junction diode ?


Answer :

Decreases or reduce


Question 18: (Marks 1)

The nuclear radius of 2713Al is 3·6 fermi. Find the nuclear radius of 6429Cu.

OR

A proton and an electron have equal speeds. Find the ratio of de Broglie wavelengths associated with them.


Answer :

The nuclear radius of


Question 19: (Marks 1)

The variation of the stopping potential (Vo) with the frequency (v) of the light incident on two different photosensitive surfaces M1 and M2 is shown in the figure. Identify the surface which has greater value of the work function.

The variation of the stopping potential (Vo


Answer :

M2


Question 20: (Marks 1)

Why cannot we use Si and Ge in fabrication of visible LEDs ?


Answer :

Si & Ge cannot be used for fabrication of visible LED because their energy gap is less 1.8eV

SECTION B

Question 21: (Marks 2)

Explain the principle of working of a meter bridge. Draw the circuit diagram for determination of an unknown resistance using it.


Answer :

Explain the principle of working of a meter bridge. Draw the circuit


Question 22: (Marks 2)

The space between the plates of a parallel plate capacitor is completely filled in two ways. In the first case, it is filled with a slab of dielectric constant K. In the second case, it is filled with two slabs of equal thickness and dielectric constants K1 and K2 respectively as shown in the figure. The capacitance of the capacitor is same in the two cases. Obtain the relationship between K, K1 and K2.

The space between the plates of a parallel plate capacitor is completely


Answer :

The space between the plates of a parallel plate capacitor is completely


Question 23: (Marks 2)

Define the term ‘Half-life’ of a radioactive substance. Two different radioactive substances have half-lives T1 and T2 and number of undecayed atoms at an instant, N1 and N2, respectively. Find the ratio of their activities at that instant.


Answer :

Define the term ‘Half-life’ of a radioactive substance. Two different


Question 24: (Marks 2)

Define wavefront of a travelling wave. Using Huygens principle, obtain the law of refraction at a plane interface when light passes from a denser to rarer medium.

OR

Using lens maker’s formula, derive the thin lens formula


Answer :

Define wavefront of a travelling wave. Using Huygens principle, obtain


Question 25: (Marks 2)

Two long straight parallel wires A and B separated by a distance d, carry equal current I flowing in same direction as shown in the figure.

Two long straight parallel wires A and B separated by a distance d, carry

(a) Find the magnetic field at a point P situated between them at a distance x from one wire.

(b) Show graphically the variation of the magnetic field with distance x for 0 < x < d.


Answer :

Two long straight parallel wires A and B separated by a distance d, carry


Question 26: (Marks 2)

Using Bohr’s atomic model, derive the expression for the radius of nth orbit of the revolving electron in a hydrogen atom.

OR

(a) Write two main observations of photoelectric effect experiment which could only be explained by Einstein’s photoelectric equation.

(b) Draw a graph showing variation of photocurrent with the anode potential of a photocell.


Answer :

Using Bohr’s atomic model, derive the expression for the radius of


Question 27: (Marks 2)

Explain the terms ‘depletion layer’ and ‘potential barrier’ in a p-n junction diode. How are the (a) width of depletion layer, and (b) value of potential barrier affected when the p-n junction is forward biased ?


Answer :

Explain the terms ‘depletion layer’ and ‘potential barrier’ in a

SECTION C

Question 28: (Marks 3)

(a) Two cells of emf E1 and E2 have their internal resistances r1 and r2 , respectively. Deduce an expression for the equivalent emf and internal resistance of their parallel combination when connected across an external resistance R. Assume that the two cells are supporting each other.

(b) In case the two cells are identical, each of emf E = 5 V and internal resistance r = 2 Ω, calculate the voltage across the external resistance R = 10 Ω.


Answer :

Two cells of emf E1 and E2 have their internal resistances r1 and


Question 29: (Marks 3)

(a) Write an expression of magnetic moment associated with a current (I) carrying circular coil of radius r having N turns. (b) Consider the above mentioned coil placed in YZ plane with its centre at the origin. Derive expression for the value of magnetic field due to it at point (x, 0, 0).

OR

(a) Define current sensitivity of a galvanometer. Write its expression. (b) A galvanometer has resistance G and shows full scale deflection for current Ig .

(i) How can it be converted into an ammeter to measure current up to I0 (I0 > Ig) ?

(ii) What is the effective resistance of this ammeter ?


Answer :

Write an expression of magnetic moment associated with a


Question 30: (Marks 3)

A resistance R and a capacitor C are connected in series to a source V = V0 sin ωt. Find :

(a) The peak value of the voltage across the (i) resistance and (ii) capacitor.

(b) The phase difference between the applied voltage and current. Which of them is ahead ?


Answer :

A resistance R and a capacitor C are connected in series to a source


Question 31: (Marks 3)

What is the effect on the interference fringes in Young’s double slit experiment due to each of the following operations ? Justify your answers.

(a) The screen is moved away from the plane of the slits.

(b) The separation between slits is increased.

(c) The source slit is moved closer to the plane of double slit.


Answer :

What is the effect on the interference fringes in Young’s double slit


Question 32: (Marks 3)

(a) Write the expression for the speed of light in a material medium of relative permittivity εr and relative magnetic permeability μr .

(b) Write the wavelength range and name of the electromagnetic waves which are used in (i) radar systems for aircraft navigation, and (ii) Earth satellites to observe the growth of the crops.


Answer :

Write the expression for the speed of light in a material medium of


Question 33: (Marks 3)

The nucleus


Answer :

The nucleus


Question 34: (Marks 3)

(a) Draw circuit diagram and explain the working of a zener diode as a dc voltage regulator with the help of its I-V characteristic.

(b) What is the purpose of heavy doping of p- and n-sides of a zener diode ?


Answer :

Draw circuit diagram and explain the working of a zener diode as a

SECTION D

Question 35: (Marks 5)

(a) Using Gauss law, derive expression for electric field due to a spherical shell of uniform charge distribution α and radius R at a point lying at a distance x from the centre of shell, such that

(i) 0 < x < R, and

(ii) x > R.

An electric field is uniform and acts along + x direction in the


Answer :

An electric field is uniform and acts along + x direction in the


Question 36: (Marks 5)

(a) Derive the expression for the torque acting on the rectangular current carrying coil of a galvanometer. Why is the magnetic field made radial ?

(b) An α-particle is accelerated through a potential difference of 10 kV and moves along x-axis. It enters in a region of uniform magnetic field B = 2 × 10–3 T acting along y-axis. Find the radius of its path. (Take mass of α-particle = 6·4 × 10–27 kg )

OR

(a) With the help of a labelled diagram, explain the working of a step-up transformer. Give reasons to explain the following :

(i) The core of the transformer is laminated.

(ii) Thick copper wire is used in winding

(b) A conducting rod PQ of length 20 cm and resistance 0·1 Ω rests on two smooth parallel rails of negligible resistance AA’ and CC’. It can slide on the rails and the arrangement is positioned between the poles of a permanent magnet producing uniform magnetic field B = 0·4 T. The rails, the rod and the magnetic field are in three mutually perpendicular directions as shown in the figure. If the ends A and C of the rails are short circuited, find the

(i) external force required to move the rod with uniform velocity v = 10 cm/s, and

(ii) power required to do so.

power required to do so.


Answer :

Derive the expression for the torque acting on the rectangular


Question 37: (Marks 5)

(a) Draw the ray diagram of an astronomical telescope when the final image is formed at infinity. Write the expression for the resolving power of the telescope.

(b) An astronomical telescope has an objective lens of focal length 20 m and eyepiece of focal length 1 cm.

(i) Find the angular magnification of the telescope.

(ii) If this telescope is used to view the Moon, find the diameter of the image formed by the objective lens. Given the diameter of the Moon is 3·5 × 106 m and radius of lunar orbit is 3·8 × 108 m. 5

OR

An object is placed in front of a concave mirror. It is observed that


Answer :

Draw the ray diagram of an astronomical telescope when the final

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CBSE Class 12 Board Exam Physics Paper 2018 2019 2020 with Solutions

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