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Physics Sample Paper For Class 12 With Solution NCERT CBSE Board 2020

Here we are providing CBSE Previous Year Question Papers Class 6 to 12 solved with soutions Physics Sample Paper for Class 12 With Solution NCERT CBSE Board 2020 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 4 with Solutions

SECTION – A

Select the most appropriate option from those given below each question.

Question 1: (Marks 1)

A cell of emf (E) and internal resistance r is connected across a variable


Answer :

A cell of emf (E) and internal resistance r is connected across a variable


Question 2: (Marks 1)

A uniform wire of resistance 2R is bent in the form of a circle


Answer :

A uniform wire of resistance 2R is bent in the form of a circle


Question 3: (Marks 1)

A current I flows through a long straight conductor which is bent into a


Answer :

A current I flows through a long straight conductor which is bent into a


Question 4: (Marks 1)

A circular loop of radius r, carrying a current I lies in y-z plane with its centre at the origin. The net magnetic flux through the loop is :

(a) directly proportional to r

(b) zero

(c) inversely proportional to r

(d) directly proportional to I


Answer :

(b) Zero


Question 5: (Marks 1)

The kinetic energy of a proton and that of an α-particle are 4 eV and 1 eV, respectively. The ratio of the de-Broglie wavelengths associated with them, will be

(a) 2:1

(b) 1:1

(c) 1:2

(d) 4:1


Answer :

(b) 1:1


Question 6: (Marks 1)

A photocell connected in an electrical circuit is placed at a distance ‘d’ from a source of light. As a result, current I flows in the circuit. What will be the current in the circuit when the distance is reduced to ‘d/2’ ?

(a) I

(b) 2I

(c) 4I

(d) I/2


Answer :

(c) 4 I


Question 7: (Marks 1)

A current of 10A is flowing from east to west in a long straight wire kept on a horizontal table. The magnetic field developed at a distance of 10 cm due north on the table is :

(a) 2 × 10–5 T, acting downwards

(b) 2 × 10–5 T, acting upwards

(c) 4 × 10–5 T, acting downwards

(d) 4 × 10–5 T, acting upwards


Answer :

(a) 2 × 10–5 T, acting downwards


Question 8: (Marks 1)

When a wave undergoes reflection at an interface from rarer to denser


Answer :

(c) π


Question 9: (Marks 1)

Paschen series of atomic spectrum of hydrogen gas lies in :

(a) Infrared region

(b) Ultraviolet region

(c) Visible region

(d) Partly in ultraviolet and partly in visible region


Answer :

(a) Infra red region


Question 10: (Marks 1)

In the α-article scattering experiment, the shape of the trajectory of the scattered α-particles depend upon :

(a) only on impact parameter.

(b) only on the source of α-particles.

(c) both impact parameter and source of α-particles.

(d) impact parameter and the screen material of the detector.


Answer :

(a) Only on impact parameter

Note : Fill in the blanks with appropriate answer.

Question 11: (Marks 1)

Torque acting on an electric dipole placed in an electric field is maximum when the angle between the electric field and the dipole moment is _______.


Answer :

Torque acting on an electric dipole placed in an electric field is maximum


Question 12: (Marks 1)

A proton released from rest in an electric field, will start moving towards a region of _______ potential in the field.


Answer :

Decreasing/Lower


Question 13: (Marks 1)

To minimize the percentage error in the determination of unknown resistance of a conductor in meter bridge experiment, the balance point is adjusted near _______ of the wire.

OR

In potentiometer, a long uniform wire is used to _______ potential gradient along the wire.


Answer :

Middle/mid point /center

OR

Decrease


Question 14: (Marks 1)

Unpolarised light of intensity Io is incident on two crossed polaroids. The intensity of light transmitted by the combination will be _______.


Answer :

Zero


Question 15: (Marks 1)

Name the particle emitted spontaneously in the following nuclear reaction


Answer :

Name the particle emitted spontaneously in the following nuclear reaction

Answer the following :

Question 16: (Marks 1)

The work done in moving a charge particle between two points in an uniform electric field, does not depend on the path followed by the particle. Why ?


Answer :

Because the electrostatic force is conservative in nature

Alternatively:-

Electric field is conservative in nature / work done by or against the electric field does not depend upon the path followed.


Question 17: (Marks 1)

Define ‘magnetic declination’ at a place on earth.


Answer :

Magnetic declination is the angle between the magnetic meridian and the geographic meridian at a place on the earth.


Question 18: (Marks 1)

An A.C. source with variable frequency is connected to a parallel plate capacitor. How will the displacement current be affected with the decrease in frequency of the source ?


Answer :

An A.C. source with variable frequency is connected to a parallel plate


Question 19: (Marks 1)

An astronomical telescope may be a refracting type or a reflecting type. Which of the two produces image of better quality ? Justify your answer.


Answer :

Reflecting type telescope

Reason/Justification :-

Mirror have large aperture/high resolving power/ free from chromatic aberration /free from spherical aberration. ( Any one)


Question 20: (Marks 1)

Can a slab of p-type semi-conductor be physically joined to another n-type semiconductor slab to form p-n junction ? Justify your answer.

OR

In a p-n junction diode the forward bias resistance is low as compared to the reverse bias resistance. Give reason.


Answer :

No

As there will be discontinuity for the flow of charge carriers / no contact at atomic level.

(Any One Justification)

OR

The forward current is large due to majority charge carriers which are very large in number. Hence resistance in forward bias is low. Alternatively: Depletion region decreases or barrier potential decreases.

SECTION : B

Question 21: (Marks 2)

Find the total charge stored in the network of capacitors connected


Answer :

Find the total charge stored in the network of capacitors connected


Question 22: (Marks 2)

A wire of length Lo has a resistance Ro. It is gradually stretched till its length becomes 2 Lo.

(a) Plot a graph showing variation of its resistance R with its length l during stretching.

(b) What will be its resistance when its length becomes 2 Lo?


Answer :

A wire of length Lo


Question 23: (Marks 2)

A resistor R and an inductor L are connected in series to a source of voltage V = Vo sin ωt. The voltage is found to lead current in phase by π/4. If the inductor is replaced by a capacitor C, the voltage lags behind current in phase by π/4. When L, C and R are connected in series with the same source,

Find the :

(i) average power dissipated and

(ii) instantaneous current in the circuit.


Answer :

A resistor R and an inductor L are connected in series to a source of voltage


Question 24: (Marks 2)

Light of same wavelength is incident on three photo-sensitive surfaces A, B and C. The following observations are recorded.

(i) From surface A, photo electrons are not emitted.

(ii) From surface B, photo electrons are just emitted.

(iii) From surface C, photo electrons with some kinetic energy are emitted.

Compare the threshold frequencies of the three surfaces and justify your answer.

OR

If the frequency of light incident on the cathode of a photo-cell is increased, how will the following be affected ? Justify your answer.

(i) Energy of the photo electrons.

(ii) Photo current.


Answer :

Light of same wavelength is incident on three photo-sensitive surfaces A


Question 25: (Marks 2)

Briefly explain how a potential barrier is set up across a p-n junction as a result of diffusion and drift of the charge carriers.


Answer :

Diffusion current is set up across the junction due to the concentration difference of the majority charge carriers on the two sides of the junction.

This diffusion develops an electric field from n- side to p- side across the junction which creates a drift current in the opposite direction.

When diffusion and drift current become equal in magnitude the potential difference across the junction is the barrier potential.


Question 26: (Marks 2)

(a) Why is a photo diode operated under reverse bias condition ?

(b) Draw V-I characteristic curves of photo diode for incident light of intensities I1 and I2 (I1 > I2).

OR

(a) State the level of doping and biasing condition used in light emitting diode (LED).

(b) Write any two advantages of LED over the conventional low power lamps.


Answer :

(a) Because the fractional change in the minority carriers dominated very weak reverse current is more easily measurable than fractional change in forward biased large current

(b)
Draw V-I characteristic curves of photo diode for incident light o

I1I2

OR

(a) It is a heavily doped p-n junction. It operates in forward biasing

(b) Advantages Low operational voltage/less power /fast action / nearly monochromatic / long life ( Any two)


Question 27: (Marks 2)

(a) Explain the formation of energy bands in crystalline solids.

(b) Draw the energy band diagrams of (i) a metal and (ii) a semiconductor


Answer :

Explain the formation of energy bands in crystalline solids

SECTION – C

Question 28: (Marks 3)

A hollow conducting sphere of inner radius r1 and outer radius r2 has a charge Q on its surface. A point charge –q is also placed at the centre of the sphere.

(a) What is the surface charge density on the (i) inner and (ii) outer surface of the sphere ?

(b) Use Gauss’ law of electrostatics to obtain the expression for the electric field at a point lying outside the sphere.

OR

(a) An infinitely long thin straight wire has a uniform linear charge density λ. Obtain the expression for the electric field (E) at a point lying at a distance x from the wire, using Gauss’ law.

(b) Show graphically the variation of this electric field E as a function of distance x from the wire.


Answer :

A hollow conducting sphere of inner radius r1


Question 29: (Marks 3)

(a) Explain the principle of working of a potentiometer.

(b) In a potentiometer, a standard source of emf 5V and negligible internal resistance maintains a steady current through the potentiometer wire of length 10m. Two primary cells of emf E1 and E2 are joined together in a series with (i) same polarity and (ii) opposite polarity. The combination is connected to the potentiometer circuit in each case. The balancing length of the wire in the two cases are found to be 700 cm and 100 cm, respectively. Find the values of emf of the two cells.


Answer :

Explain the principle of working of a potentiometer


Question 30: (Marks 3)

(a) Differentiate between self inductance and mutual inductance.

(b) The mutual inductance of two coaxial coils is 2H. The current in one coil is changed uniformly from zero to 0.5A in 100 ms. Find the :

(i) change in magnetic flux through the other coil.

(ii) emf induced in the other coil during the change.


Answer :

Differentiate between self inductance and mutual inductance


Question 31: (Marks 3)

Explain with the help of a diagram, the working of a step-down transformer. Why is a laminated iron core used in a transformer ?


Answer :

Explain with the help of a diagram, the working of a step-down


Question 32: (Marks 3)

Name the electro-magnetic waves with their frequency range, produced in

(a) some radioactive decay

(b) sparks during electric welding

(c) TV remote


Answer :

(a) Gamma rays, frequency range 1019 to 1024 Hz

(a) UV rays, frequency range 1015 to 1017 Hz

(b) Infrared rays, frequency range 1012 to 1014 Hz


Question 33: (Marks 3)

Two coherent light waves of intensity 5 × 10–2 Wm–2 each super-impose and produce the interference pattern on a screen. At a point where the path difference between the waves is λ/6, λ being wavelength of the wave, find the

(a) phase difference between the waves.

(b) resultant intensity at the point.

(c) resultant intensity in terms of the intensity at the maximum.


Answer :

Two coherent light waves of intensity 5 × 10–2 Wm–2 each super-impose


Question 34: (Marks 3)

Two objects P and Q when placed at different positions in front of a concave mirror of focal length 20 cm, form real images of equal size. Size of object P is three times size of object Q. If the distance of P is 50 cm from the mirror, find the distance of Q from the mirror.


Answer :

Two objects P and Q when placed at different positions in front of a

SECTION-D

Question 35: (Marks 5)

(a) Show that a current carrying solenoid behaves like a small bar magnet. Obtain the expression for the magnetic field at an external point lying on its axis.

(b) A steady current of 2A flows through a circular coil having 5 turns of radius 7 cm. The coil lies in X-Y plane with its centre at the origin. Find the magnitude and direction of the magnetic dipole moment of the coil.

OR

(a) Derive the expression for the force acting between two long parallel current carrying conductors. Hence, define 1 A current.

(b) A bar magnet of dipole moment 3 Am2 rests with its centre on a frictionless pivot. A force F is applied at right angles to the axis of the magnet, 10 cm from the pivot. It is observed that an external magnetic field of 0.25 T is required to hold the magnet in equilibrium at an angle of 30° with the field.

Calculate the value of F.

How will the equilibrium be effected if F is withdrawn ?


Answer :

Show that a current carrying solenoid behaves like a small bar


Question 36: (Marks 5)

Draw the ray diagram showing refraction of ray of light through a


Answer :

Draw the ray diagram showing refraction of ray of light through a


Question 37: (Marks 5)

Derive the law of radioactive decay


Answer :

Derive the law of radioactive decay

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Physics Sample Paper for Class 12 With Solution NCERT CBSE Board 2020

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