Please refer to Class 12 Physics Sample Paper with solutions provided below. All sample papers for Physics Class 12 have been designed as per the latest paper pattern issued by CBSE for the current academic year. Students should practice these guess papers for Class 12 Physics as it will help them to gain more understanding of the type of questions that are expected to be asked in upcoming Class 12 Physics exams. Please click on the links below to access free CBSE Sample Papers for Class 12 Physics.
Class 12 Physics Sample Paper Term 2 With Solutions Set A
Section-A
Question. Mention the important considerations required while fabricating a p-n junction diode to be used as a Light Emitting Diode (LED). What should be the order of band gap of an LED if it is required to emit light in the visible range?
Answer. (i) The semiconductors used for fabrication of visible LEDs must have a band gap from 1.8 eV to 3 eV.
(ii) Both p-type and n-type semiconductor are heavily doped.
(iii) It should be encapsulated with a transparent material.
For emitting light in visible range the band gap should be from 1.8 eV to 3 eV.
Question. A monochromatic source, emitting light of wavelength, 600 nm, has a power output of 66W. Calculate the number of photons emitted by this source in 2 minutes. Use h = 6.6 × 10–34 Js.
Answer. Here, l = 600 nm = 6 × 10–7 m; P = 66 W,
N = ?, T = 2 × 60s
Energy of each photon,
Question. Distinguish between intrinsic and extrinsic semiconductors on the basis of energy band diagram.
Answer.
Section-B
Question. Radiations of frequency v1 and v2 are made to fall in turn, on a photosensitive surface. The stopping potentials required for stopping the most energetic photoelectrons in the two cases are V1 and V2 respectively. Obtain a formula for determining the threshold frequency in terms of these parameters.
Answer. If v0 is the threshold frequency, then from photoelectric equation, we have
Question. Two material bars A and B of equal area of cross-section, are connected in series to a DC supply. A is made of usual resistance wire and B of an n-type semiconductor.
(a) In which bar is drift speed of free electrons greater?
(b) If the same constant current continues to flow for a long time, how will the voltage drop across A and B be affected?
Justify each answer.
Answer. (a) Drift speed in B (n-type semiconductor) is higher
Reason: I = neAvd is same for both n is much lower in semiconductors.
(b) Voltage drop across A will increase as the resistance of A increases with increase in temperature.
Voltage drop across B will decrease as resistance of B will decrease with increase in temperature.
Question. Calculate and compare the energy released by
(a) fusion of 1 kg of hydrogen deep within the sun and
(b) the fission of 1 kg of 235U in a fission reactor.
Answer. (a) In sun 4 hydrogen nuclei combine to form a helium nucleus and 26 MeV of energy is released
Question. A convex lens made up of glass of refractive index. 1.5 is dipped in turn in (i) a medium of refractive index 1.65
(ii) a medium of refractive index 1.33 (a) will it behave as a converging or diverging lens in two cases (b) How will its focal length changes in two media.
Answer. (i) refractive index of medium = μ1 = 1.65, μ2 = 1.5,
R1 = R, R2 = – R
Question. Draw a schematic diagram of a reflecting telescope (Cassegrain). Write two important advantages that a reflecting telescope has over a refracting telescope.
Answer. Objective is concave mirror of large focal length and large aperture having a hole around its pole. The light coming from a far off object after reflection from the objective is made to fall on a secondary mirror (convex)placed in between its pole and focus. The light reflected from the convex mirror goes into the eye piece, which acts as a simple microscope.
Advantage of reflecting telescope over a refracting telescope:
(i) Reflecting telescope is free from chromatic aberration.
(ii) Image is free from spherical aberration.
(iii) Image formed is brighter and resolving power is high.
Question. How is a wavefront defined? Using Huygen’s construction draw a figure showing the propagation of a plane wave reflecting at the interface of the two media. Show that the angle of incidence is equal to angle of reflection.
Answer. Consider a plane wavefront AB reflected at the interface of the two media. When the wavefront strikes the reflected surface at point B the secondary wavelets travel back into the some medium.
During the time the disturbance from A reach the point C, the secondary wavelets from B have spread over a hemisphere of radius BD = vt. Where v in the speed of the wave and t is the time taken from the wave to reach from A to C.
Also AC = vt
The tangent plane CD is the new reflected wave front.
Let i and r be the angle of incidence and angle of reflection respectively.
∠ABC = ∠i, ∠BCD = ∠r
In DABC and DDCB, ∠BAC = ∠CDB = 90°
BC = BC common
AC = BD = vt
So DABC ≅ DDCB
So by cpct ∠ABC = ∠BCD or ∠i = ∠r
Question. A monochromatic radiation of wavelength 975 Å excites the hydrogen atom from its ground state to a higher state. How many different spectral lines are possible in the resulting spectrum? Which transition corresponds to the longest wavelength amongst them?
Ans. Energy corresponding to the given wavelength:
Question. Identify the following electromagnetic radiation as per the wavelength given below:
(a) 10– 4 nm (b) 10–3 m (c) 1 nm.
Write one application of each.
Answer. (a) 10– 4 nm → gamma radiation
Application : Radio therapy or to initiate nuclear reactions.
(b) 10–3 m → microwaves
Application : in RADAR for aircraft navigation, microwave cooking (oven).
(c) 1 nm → X-rays
Application : In medical science for detection of fractures in bones.
Section-C
Question. Radio waves are produced by the accelerated motion of charges in conducting wires. Microwaves are produced by special vacuum tubes. Infrared waves are produced by hot bodies and molecules also known as heat waves. UV rays are produced by special lamps and very hot bodies like sun.
Based on the above facts, answer the following questions:
(i) Solar radiation is:
(a) transverse em wave
(b) longitudinal em wave
(c) both (a) and (b)
(d) none of these
Answer
A
(ii) The cause of greenhouse effect is
(a) infrared rays
(b) ultraviolet rays
(c) X-rays
(d) radio waves
Answer
A
(iii) Biological importance of ozone layer is
(a) it stops UV rays
(b) it reflects radio waves
(c) its layer reduces greenhouse effect
(d) none of these
Answer
A
(iv) Ozone is found in
(a) stratosphere
(b) ionosphere
(c) mesosphere
(d) troposphere
Answer
A
(v) Earth’s atmosphere is richest in
(a) ultraviolet rays
(b) infrared rays
(c) X-rays
(d) microwaves
Answer
B
