CBSE Class 12 Previous Year Question Papers With Solutions Pdf Physics

Question 1: (Marks 1)

Answer :

(D) R = 0

Question 2: (Marks 1)

In a current carrying conductor, the ratio of the electric field and the current density at a point is called

(A) Resistivity

(B) Conductivity

(C) Resistance

(D) Mobility

Answer :

(A) Resistivity

Question 3: (Marks 1)

An electron is released from rest in a region of uniform electric and magnetic fields acting parallel to each other. The electron will

(A) move in a straight line.

(B) move in a circle.

(C) remain stationary.

(D) move in a helical path.

Answer :

(A) move in a straight line

Question 4: (Marks 1)

Above Curie temperature, a

(A) ferromagnetic material becomes diamagnetic.

(B) ferromagnetic material becomes paramagnetic.

(C) paramagnetic material becomes ferromagnetic.

(D) paramagnetic material becomes diamagnetic.

Answer :

(B) ferromagnetic material becomes paramagnetic

Question 5: (Marks 1)

Displacement current exists only when

(A) electric field is changing.

(B) magnetic field is changing.

(C) electric field is not changing.

(D) magnetic field is not changing.

Answer :

(A) electric field is changing

Question 6: (Marks 1)

Electromagnetic waves used as a diagnostic tool in medicine are

(A) X-rays.

(B) ultraviolet rays.

(C) infrared radiation.

(D) ultrasonic waves.

Answer :

(A) X – rays

Question 7: (Marks 1)

At equilibrium, in a p-n junction diode the net current is

(A) due to diffusion of majority charge carriers.

(B) due to drift of minority charge carriers.

(C) zero as diffusion and drift currents are equal and opposite.

(D) zero as no charge carriers cross the junction.

Answer :

(C) zero as diffusion and drift current are equal and opposite.

Question 8: (Marks 1)

In an n-type semiconductor, the donor energy level lies

(A) at the centre of the energy gap.

(B) just below the conduction band.

(C) just above the valance band.

(D) in the conduction band.

Answer :

(B) just below the conduction band

Question 9: (Marks 1)

When two nuclei (A ≤ 10) fuse together to form a heavier nucleus, the

(A) binding energy per nucleon increases.

(B) binding energy per nucleon decreases.

(C) binding energy per nucleon does not change.

(D) total binding energy decreases.

Answer :

(A) binding energy per nucleon increases

Question 10: (Marks 1)

In β^- decay, a

(A) neutron converts into a proton emitting antineutrino.

(B) neutron converts into a proton emitting neutrino.

(C) proton converts into a neutron emitting antineutrino.

(D) proton converts into a neutron emitting neutrino.

Answer :

(A) neutron converts into a proton emitting antineutrino.

Question 11: (Marks 1)

If the electric flux entering and leaving a closed surface in air are ø1 and ø2 respectively, the net electric charge enclosed within the surface is ___________ .

Answer :

(ø₂ − ø₁)ε₀/ (ø₁ − ø₂)ε₀

Question 12: (Marks 1)

Answer :

Question 13: (Marks 1)

For a higher resolving power of a compound microscope, the wavelength of light used should be ___________ .

Answer :

Small/ shorter

Question 14: (Marks 1)

Unpolarised light passes from a rarer into a denser medium. If the reflected and the refracted rays are mutually perpendicular, the reflected light is linearly polarised ___________ to the plane of incidence.

Answer :

Perpendicular

Question 15: (Marks 1)

Out of red, blue and yellow lights, the scattering of ___________ light is maximum.

Answer :

Blue

Question 16: (Marks 1)

What is the impedance of a capacitor of capacitance C in an ac circuit using source of frequency n Hz ?

OR

What is the value of impedance of a resonant series LCR circuit ?

Answer :

Question 17: (Marks 1)

Answer :

Zero

Question 18: (Marks 1)

Draw the graph showing variation of the value of the induced emf as a function of rate of change of current flowing through an ideal inductor.

Answer :

Question 19: (Marks 1)

What is the wavelength of a photon of energy 3·3 × 10^–19 J ?

Answer :

6.03 × 10^-7 m

[Award full 1 mark even if a student writes 6 × 10^-7 m]

Question 20: (Marks 1)

Define the term ‘threshold frequency’ in photoelectric emission.

Answer :

For a given photosensitive material, there exists a certain minimum cut-off frequency of the incident radiation, called the threshold frequency, below which no emission of photo electrons takes place, no matter how intense the incident light is.

Question 21: (Marks 2)

Define the term ‘mobility’ of charge carriers in a current carrying conductor. Obtain the relation for mobility in terms of relaxation time.

OR

Define the term ‘drift velocity’ of electrons in a current carrying conductor. Obtain the relationship between the current density and the drift velocity of electrons.

Answer :

Question 22: (Marks 2)

An ammeter of resistance 0·8 Ω can measure a current up to 1·0 A. Find the value of shunt resistance required to convert this ammeter to measure a current up to 5·0 A.

Answer :

Question 23: (Marks 2)

(a) Explain the term ‘sharpness of resonance’ in ac circuit.

(b) In a series LCR circuit, V_L = V_C ≠ V_R. What is the value of power factor for this circuit ?

OR

An ac source of emf V = V₀ sin ωt is connected to a capacitor of capacitance C. Deduce the expression for the current (I) flowing in it. Plot the graph of (i) V vs. ωt, and (ii) I vs. ωt.

Answer :

Question 24: (Marks 2)

Which of the following electromagnetic waves has (a) minimum wavelength, and (b) minimum frequency ? Write one use of each of these two waves.

Infrared waves, Microwaves, y-rays and X-rays

Answer :

Question 25: (Marks 2)

An object is kept 20 cm in front of a concave mirror of radius of curvature 60 cm. Find the nature and position of the image formed.

Answer :

Question 26: (Marks 2)

Answer :

Question 27: (Marks 2)

Draw V-I characteristics of a p-n junction diode. Explain, why the current under reverse bias is almost independent of the applied voltage up to the critical voltage.

Answer :

Question 28: (Marks 3)

Answer :

Question 29: (Marks 3)

(a) Derive the condition of balance for Wheatstone bridge.

(b) Draw the circuit diagram of a meter bridge to explain how it is based on Wheatstone bridge.

Answer :

Question 30: (Marks 3)

Answer :

Question 31: (Marks 3)

What is the difference in the construction of an astronomical telescope and a compound microscope ? The focal lengths of the objective and eyepiece of a compound microscope are 1·25 cm and 5·0 cm, respectively. Find the position of the object relative to the objective in order to obtain an angular magnification of 30 when the final image is formed at the near point.

Answer :

Question 32: (Marks 3)

The maximum kinetic energy of the photoelectrons emitted is doubled when the wavelength of light incident on the photosensitive surface changes from λ1 to λ2 . Deduce expressions for the threshold wavelength and work function for the metal surface in terms of λ1 and λ2 .

Answer :

Question 33: (Marks 3)

(a) Differentiate between half-life and average life of a radioactive substance.

(b) A radioactive substance decays for an interval of time equal to its mean life. Find the fraction of the amount of the substance which is left undecayed after this time interval.

Answer :

Question 34: (Marks 3)

What is the function of a solar cell ? Briefly explain its working and draw its I-V characteristic curve.

Answer :

Question 35: (Marks 5)

(a) Use Gauss’s law to show that due to a uniformly charged spherical shell of radius R, the electric field at any point situated outside the shell at a distance r from its centre is equal to the electric field at the same point, when the entire charge on the shell were concentrated at its centre. Also plot the graph showing the variation of electric field with r, for r ≤ R and r ≥ R.

(b) Two point charges of + 1 μC and + 4 μC are kept 30 cm apart. How far from the + 1 μC charge on the line joining the two charges, will the net electric field be zero ?

Answer :

Question 36: (Marks 5)

(a) A circular loop of radius R carries a current I. Obtain an expression for the magnetic field at a point on its axis at a distance x from its centre.

(b) A conducting rod of length 2 m is placed on a horizontal table in north-south direction. It carries a current of 5 A from south to north. Find the direction and magnitude of the magnetic force acting on the rod. Given that the Earth’s magnetic field at the

OR

(a) Obtain the expression for the deflecting torque acting on the current carrying rectangular coil of a galvanometer in a uniform magnetic field. Why is a radial magnetic field employed in the moving coil galvanometer ?

(b) Particles of mass 1·6 × 10^–27 kg and charge 1·6 × 10^–19 C are accelerated in a cyclotron of dee radius 40 cm. It employs a magnetic field 0·4 T. Find the kinetic energy (in MeV) of the particle beam imparted by the accelerator.

Answer :

Question 37: (Marks 5)

(a) Derive lens maker’s formula for a biconvex lens.

(b) A point object is placed at a distance of 12 cm on the principal axis of a convex lens of focal length 10 cm. A convex mirror is placed coaxially on the other side of the lens at a distance of 10 cm. If the final image coincides with the object, sketch the ray diagram and find the focal length of the convex mirror.

OR

(a) What is a wavefront ? How does it propagate ? Using Huygens’ principle, explain reflection of a plane wavefront from a surface and verify the laws of reflection.

(b) A parallel beam of light of wavelength 500 nm falls on a narrow slit and the resulting diffraction pattern is obtained on a screen 1 m away. If the first minimum is formed at a distance of 2·5 mm from the centre of the screen, find the (i) width of the slit, and (ii) distance of first secondary maximum from the centre of the screen.

Answer :

CBSE Class 12 Previous Year Question Papers With Solutions pdf Physics

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 sample paper 2020, class 12 important questions Physics, cbse class 12 board exam Physics paper, Physics previous year question papers class 12 with solutions, Physics sample paper class 12 2019, cbse class 12 Physics question paper 2017 solved pdf, cbse class 12 Physics question paper 2018, class 12 Physics paper 2019, Physics question paper for class 12, cbse class 12 Physics paper 2019

Ncert Solution for class 6 to 12 download in pdf