Class – XII

Sample Paper - 3

­General Instructions:

Read the following instructions very carefully and strictly follow them:

(i) This question paper comprises four Sections – A, B, C and D.

(ii) There are 37 questions in the question paper. All questions are compulsory.

(iii) Section A – Questions no. 1 to 20 are very short answer type questions, carrying one mark each.

(iv) Section B – Questions no. 21 to 27 are short answer type questions, carrying two marks each.

(v) Section C – Questions no. 28 to 34 are long answer type questions, carrying three marks each.

(vi) Section D – Questions no. 35 to 37 are also long answer type questions, carrying five marks each.

(vii) There is no overall choice in the question paper.

(viii) In addition to this, separate instructions are given with each section and

question, wherever necessary.

(ix) Use of calculators and log tables is not permitted.

(x) You may use the following values of physical constants wherever necessary.

Mass of neutron = 1.675 × 10⁻²⁷ kg

Mass of proton = 1.673 × 10²⁷ kg

Avogadro’s number = 6.023 × 10²³ per gram mole

Boltzmann constant = 1.38 × 10⁻²³ JK^-1

Section - A

Question 1:

The rubber used in the wheels of aero-plane is _________
(a) perfect insulator
(b) slightly conducting
(c) can be an insulator or conducting
(d) semiconductor

 

Question 2:

8 electric dipoles having charges e are placed at the centre of a cube. The net flux coming out of the cube surface is _________
a) zero
b) 
c) 
d) 

 

Question 3:

A parallel plate capacitor has a plate area of 100 cm² and is separated by a distance of 20 mm. Find its capacitance.
(a) 6.425 × 10^-12 F
(b) 5.425 × 10^-12 F
(c) 4.425 × 10^-12 F
(d) 3.425 × 10^-12 F

 

Question 4:

‘X’ is a widely used capacitor which consists of two large plane parallel conducting plates separated by a small distance. Identify X.
(a) spherical capacitor
(b) parallel plate capacitor
(c) cylindrical capacitor
(d) electrolytic capacitor

 

Question 5:

Identify the property which is not characteristic for a semiconductor?
(a) At a very low temperature, it behaves like an insulator
(b) At higher temperatures, two types of charge carriers will cause conductivity
(c) The charge carriers are electrons and holes in the valence band at higher temperatures
(d) The semiconductor is electrically neutral

 

Question 6:

Which of the following is used in the Davisson – Germier experiment?
(a) double slit
(b) single slit
(c) electron gun
(d) electron microscope

 

Question 7:

There are two conductors X and Y carrying a current I and moving in the same direction. p and q are two electron beams also moving in the same direction. Will there be attraction or repulsion between the 2 conductors and between the two electron beams separately?

(a) the electron beams will repel each other and conductors attract each other

(b) the electron beams will attract each other and the conductors also attract each other

(c) the electron beams will attract each other and the conductors repel each other

(d) the electron beams will repel each other and the conductors also repel each other

 

Question 8:

‘X’ is an optical illusion observed in deserts or over hot extended surfaces like a coal-tarred road, due to which a traveller sees a shimmering pond of water some distance ahead of him and in which the surrounding objects like trees appear inverted. Identify X.

a) mileage

b) mirage

c) optical activity

d) total internal reflection

 

Question 9:

What type of surface is the surface of a conductor?

(a) equipotential

(b) unipolar

(c) unipotential

(d) bipolar

 

Question 10:

Identify the dimension of electrostatic potential energy from the following.

a) ML²T^-3A^-2

b) ML³T^-2A^-1

c) M^-1L²T^-3A

d) ML²T^-3A^-1

 

Question 11:

A magnet can only repel another magnet. So, ‘X’ is a surer test of magnetism. Identify X.

 

Question 12:

What should be the value of Q so that the potential energy of the system is zero?

 

Question 13:

Which material is used to make the core of transformer & why?

 

Question 14:

If an α-particle collides head-on with a nucleus, what is its impact parameter?

 

Question 15:

Calculate the focal length of a biconvex lens if the radii of its surfaces are 50 cm and 20 cm, and index of refraction of the lens glass = 1.2.

 

Question 16:

A wire has a resistance of 5.5 Ω at 19^oC and 21.5 Ω at 200^oC. Find the temperature coefficient of resistivity(α) of the material.

 

Question 17:

What is the activity of one gram of ²²⁶₈₈ Ra, whose half-life is 1622 years?

 

Question 18:

Sky waves are not used in transmitting TV signals. Why? Suggest two methods by which range of TV transmission can be increased?

 

Question 19:

Define Red shift and Blue shift in Doppler’s effect.

 

Question 20:

Why should a photodiode be operated at a reverse bias?

 

SECTION - B

Question 21:

A slit of width 3 mm is illuminated by light of λ = 600 nm at normal incidence. If the distance of the screen from the slit is 60 cm, calculate the distance between the first order minimum on both sides of central maximum.

 

Question 22:

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 = 6.3 ˆj V/m. What is B at this point?

 

Question 23:

(a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?

(b) Explain why two field lines never cross each other at any point?

 

Question 24:

Two parallel wires in free space are 10 cm apart and each carries a current of 10 A in the same direction. What is the force exerted by one wire on the other?

 

Question 25:

Distinguish between electric potential and potential energy.

 

Question 26:

The work function of caesium is 2.14 eV. Find (a) the threshold frequency for caesium, and (b) the wavelength of the incident light if the photocurrent is brought to zero by a stopping potential of 0.60 V

OR

A 10 kg satellite circles earth once every 2 h in an orbit having a radius of 8000 km. Assuming that Bohr’s angular momentum postulate applies to satellites just as it does to an electron in the hydrogen atom, find the quantum number of the orbit of the satellite.

 

Question 27:

A charged particle of charge e and mass m is moving in an electric field E and magnetic field B. Construct dimensionless quantities and quantities of dimension [T]^-1.

 

Question 28:

Write two important limitations of Rutherford nuclear model of the atom. 

 

Question 29:

(a) A comb run through one’s dry hair attracts small bits of paper. Why? What happens if the hair is wet or if it is a rainy day? (Remember, a paper does not conduct electricity.)

(b) Ordinary rubber is an insulator. But special rubber tyres of aircraft are made slightly conducting. Why is this necessary?

(c) A bird perches on a bare high-power line, and nothing happens to the bird. A man standing on the ground touches the same line and gets a fatal shock. Why?

Question 30:

Use Gauss’s law to derive the expression for the electric field (E⃗) due to a straight uniformly charged infinite line of charge  Cm^-1.

 

Question 31:

Define magnetic susceptibility of a material. Name two elements, one having positive susceptibility and the other having negative susceptibility. What does negative susceptibility signify?

 

Question 32:

Answer the following:

(a)Why are the connections between the resistors in meter bridge made of thick copper strips?

(b)Why is it generally preferred to obtain the balance point in the middle of the meter bridge wire?

(c)Which material is used for meter bridge wire and why?

 

Question 33:

A long straight wire carrying a current of 25 A rests on a table as shown in the figure. Another wire PQ of length 1 m, mass 2.5 g carries the same current but in the opposite direction. The wire PQ is free to slide up and down. To what height will PQ rise?

Question 34:

A 100-turn rectangular coil ABCD is hung from one arm of a balance. A mass 500 g is added to the other arm to balance the weight of the coil. A current 4.9 A passes through the coil and a constant magnetic field of 0.2 T acting inward is switched on such that only arm CD of length 1 cm lies in the field. How much additional mass ‘m’ must be added to regain the balance?

                                                                                                          

Section - D

Question 35:

To ensure almost 100 per cent transmissivity, photographic lenses are often coated with a thin layer of dielectric material. The refractive index of this material is intermediated between that of air and glass (which makes the optical element of the lens). A typically used dielectric film is MgF₂ (n = 1.38). What should the thickness of the film be so that at the centre of the visible spectrum (5500 A^o) there is maximum transmission

OR

In an experiment with a potentiometer, V_B = 10V. R is adjusted to be 50 Ω. A student wanting to measure voltage E₁ of a battery finds no null point possible. He then diminishes R to 10 Ω and is able to locate the null point on the last segment of the potentiometer. Find the resistance of the potentiometer wire and potential drop per unit length across the wire in the second case.

 

 

Question 36:

(a)A solenoid has a core of a material with relative permeability 400. The windings of the solenoid are insulated from the core and carry a current of 2A. If the number of turns is 1000 per metre, calculate (i) H, (ii) M, (iii) B.

(b) Write two characteristics of a material used for making permanent magnets?

OR

The magnetic moment of short bar magnet is 1.6 m². It is placed in the magnetic meridian with north pole pointing south. The neutral point is obtained at 20 cm from the centre of the magnet. Calculate the horizontal component H of earth’s field. If magnet be reversed i.e., north pole pointing north, find the position of the neutral point.

 

Question 37:

(i)If f = 0.5 m for a glass lens, what is the power of the lens?

(ii)The radii of curvature of the faces of a double convex lens are 10 cm and 15 cm. Its focal length is 12 cm. What is the refractive index of glass?

(iii) A convex lens has 20 cm focal length in air. What is focal length in water? (Refractive index of air-water = 1.33, refractive index for air-glass = 1.5.)

OR

A multirange current meter can be constructed by using a galvanometer circuit shown in the figure. We want a current meter that can measure 10 mA, 100 mA, and 1 A using a galvanometer of resistance 10Ω and that produces maximum deflection for a current of 1 mA. Find S₁, S₂, and S₃ that have to be used.

 

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