## Most Prospecting Questions in PHYSICS-II for CBSE - 2020 Sample Questions

#### SECTION A (1 Mark )

`Q.1`

`Q.2` We usually keep high voltage to carry power from power station to the device. Why

`Q.3` A light bulb and inductor coil are connected in series with AC source. What will happen to the glow of bulb if we insert iron rod in coil. `Q.4` Which property of electrons is utilized to design electron microscope?

`Q.5` Draw I-V characteristics of Zener diode.

#### SECTION B (2 Marks )

`Q.6` What do you mean by saturation property of Nuclear force. How it is related to consistency of the binding energy per nucleon for nuclei with mass number 30 < A < 170.

`Q.7` A message signal of frequency 10kHz and peak voltage of 10 Volts is used to modulate a carrier of frequency 1 MHz and peak voltage of 20 Volts. Determine
(a) modulation Index,
(b) the side bands produced.

`Q.8` A plane electromagnetic wave of frequency 25 MHz travels in free space along the x direction. At a particular point in space and time E =6.3j V/m. What is B at this point?

`Q.9` Find expression for potential energy of a dipole in external electric field. Why we took initial angle as Π/2. Find Expression for capacitance of parallel plate capacitor. Will capacitance increases or decreases when we insert dielectric slab of thickness t.

or

`Q.10` Explain why sun light reaches us in the form of white light and not as components. #### SECTION C (3 Marks )

`Q.11` Define electrostatic potential then find potential due to dipole of charge strength q and dipole length 2a.

`Q.12` (a) "Light added to light can produce darkness". Comment on the statement. (b) Estimate the distance for which ray optics is good approximation for an aperture of 4 mm and wavelength 400nm.

`Q.13` (a)Compare and contrast Biot–Savart law with coulomb’s law.
(b) An element Δl = Δx is placed at the origin and carries a large current I = 10 A. What is M. Field on y axis at a distance of 0.5 m. Δx = 1 cm. OR

(a)State Ampere Circuital law.
(b) Figure shows a long straight wire of circular cross section of radius a carrying current I.The current I is uniformly distributed across this cross section.Find M. field due to straight conductor of radius a at the distance r when r > ar < a. `Q.14` Explain origin of LC oscillation.Derive an expression for the frequency of a LC circuit connected to an AC supply of variable frequency. Prove that total energy remain constant in LC oscillations.

`Q.15` Sketch a graph between frequency of incident radiations and stopping potential for a given photosensitive material. What information can be obtained from the value of the intercept on the potential axis?
A source of light of frequency greater than the threshold frequency is at a distance of 1 m from the cathode of a photocell. The stopping potential is found to be V. If the distance of the light source from the cathode is reduced, explain giving reasons, what change will you observe in the
(i) photoelectric current,
(ii) stopping potential.

`Q.16` (a) The trajectories, traced by different α-particles, in Geiger-Marsden experiment were observed as shown in the figure.
(1) What names are given top the symbols ‘b’ and ‘θ’ shown here.
(2)What can we say about the values of b for (i) θ = 0° (ii) θ = π radians.
(b) The ground state energy of hydrogen atom is -13.6eVWhat is the kinetic and potential energy of the electron in this state? `Q.17` State the law of radioactive decay. Plot a graph showing the number (N) of undebased nuclei as a function of time (t) for a given radioactive sample having half life T1/2. Depict in the plot the number of undecayed nuclei at (i) t = 3T1/2 and (ii) t = = 5T1/2. `Q.18` Explain Sky Wave propagation in detail. Also give condition for sky wave propagation.

`Q.19` (a) What physical quantity is same for X rays ,red light and radio waves. Express refractive Index of medium in terms of electric and magnetic properties.
(b) What do you mean by displacement current. What is its origin? When an ideal capacitor is charged by a DC battery, no current flows. However when an AC source is used ,the current flows continuously. How does one explain this, based on the concept of displacement current ?

`Q.20` Explain principle, construction and working of Transformer then suggest method how we can minimize losses in transformer.

`Q.21` Draw an appropriate ray diagram to show the passage of a white ray ,incident on one of the refracting faces of a prism. Establish the relation between the angle of deviation, refractive index and angle of prism for a prism of small refracting angle.

`Q.22` Given E = 200 for x => 0 and E = – 200 for x = < 0. A right circular cylinder of length 20 cm and radius 5 cm has its centre at the origin and its axis along the axis.
(a) What is flux through each face?
(b) What is flux through the side of the cylinder?.
(c) What is net charge inside the cylinder? #### SECTION D (4 Marks )

`Q.23` Ramesh and his younger brother Raju went to a shopping mall whose doors were automatic with self close and open. Raju asked Ramesh ,that “why these doors are automatically opening and closing without even a single touch? Ramesh was a Science student and knew principle behind it so he explained the phenomenan and advantage of it to Raju
(1)What are the values and character shown by of Raju and Ramesh
(2)Explain the principle of the same and give the mathematical equation necessary for it.

#### SECTION E (5 Marks )

`Q.24` (a) What is meant by the term doping of an intrinsic semiconductor? How does it affect the conductivity of a semiconductor? A semiconductor has equal electron hole concentration 6 x 108 . On doping with certain impurity, electron concentration increases to 9 x 1012 / m3.
(i) Identify the new semiconductor obtained after doping
(ii) Calculate the New Hole concentration
(iii) How does the energy gap vary with doping
(b) Write the truth table for the circuit given in figs. (a) and (b) consisting of NOR gate only. Identify the logic operations (OR, AND, NOT) performed by the circuits and then find output. or

(a)Why is a photo diode operated in reverse bias mode? Draw characteristic curve showing reverse bias current under different illumination intensity I1, I2, I3 and I4
(b)A photodiode is fabricated from a semiconductor with band gap of 2.8eV. Can it detect a wavelength of 6000 nm? justify your answer
(c) Two amplifier are connected one after the other in series (cascade) the first amplifier has a voltage gain of 10 and second has a voltage gain 20. If the input signal is 0.01 Volt ,calculate the output of ac signal.

`Q.25`(a) Draw neat and labeled diagram of cyclotron then explain its principle and working. What is need of radial magnetic field and soft iron cylindrical core in it .Explain resonance condition in it .Also find expression for maximum Kinetic energy of particles accelerated by Cyclotron.
(b) A cyclotron’s oscillator frequency is 10 MHz. What should be the operating magnetic field for accelerating protons? If the radius if the ‘deeds’ is 60 cm, what is the kinetic energy of the proton beam produced by the accelerator ( e = 1.60 x 10-19C, mp = 1.67 x 10-27kg). Express your answer in units of MeV (1 MeV = 1.602 × 10–13 J).

or

(a) State Biot and Savart law. Use it to find Magnetic field on the axis of current carrying circular loop.
(b) The wire loop PQRSP formed by joining two semicircular wires of radii R1 and R2 carries a current I, as shown in fig. Find the magnitude and direction of the magnetic field at the centre O.

`Q.26` (a) Explain construction and working of Astronomical Telescope. Derive expression for its magnification power at normal adjustment .Write two important limitations of refracting type telescope over reflecting type.
(b)A small telescope has an objective lens of focal length 144 cm and an eye piece of focal length 6 cm. What is the magnifying power of the telescope? What is separation between the objective and eye piece.

or

(a) What do you mean by coherent and Incoherent addition of wares. Find conditions of constructive and destructive interference. Show that resultant displacement is 2a cos Φ/2. When a low flying air-craft passes overhead. We sometimes notice a slight shaking of the picture on our T.V. screen. Suggest a possible explanation.
(b) Yellow light of wavelength 6000A produces fringes of width 0.8mm in young’s double slit experiment. What will be the fringe width if the light source is replaced by another monochromatic source of wavelength 7500A and separation between slit is doubled?

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