Class – XII

Sample Paper - 2

­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:

What is the dielectric constant of metal?

(a) 0

(b) 1

(c) -1

(d) infinite

 

Question 2:

Which among the following molecule is not a dipole?
(a) NH₃
(b) H₂O
(c) HCl
(d) CH₄

 

Question 3:

Identify the material which is suitable for making standard resistors.
(a) Silver
(b) Copper
(c) Constantan
(d) Germanium

 

 

Question 4:

How is a galvanometer converted into an ammeter?
(a) By connecting a high resistance shunt in parallel to the galvanometer
(b) By connecting a low resistance shunt in parallel to the galvanometer
(c) By connecting a high resistance shunt in series with the galvanometer
(d) By connecting a low resistance shunt in series with the galvanometer

 

Question 5:

Which among the following is true about magnetic susceptibility?

(a) It is the ratio of magnetic intensity to intensity of magnetization

(b) The SI unit of magnetic susceptibility is Tesla (T)

(c) It is the ratio of intensity of magnetization to magnetic intensity

(d) It is the ratio of magnetic moment to volume

 

Question 6:

Which law is used in finding the direction of current in an a.c. generator?
(a) Maxwell’s law
(b) Lenz’s law
(c) Corkscrew law
(d) Ampere circuital law

 

Question 7:

When are the voltage and current in LCR-series ac circuit in phase?

(a) X_L = X_C

(b) X_L > X_C

(c) X_L < X_C

(d) Indeterminant

 

Question 8:

Identify the electromagnetic wave which is also known as heatwaves.

(a) Radio Waves

(b) Gamma Waves

(c) X-Rays

(d) Infrared Waves

 

Question 9:

Which type of waves shows the property of polarization?

(a) Infrared

(b) Longitudinal

(c) Transverse

(d) Microwave

 

Question 10:

Which of the following is true regarding the Bohr model of atoms?

(a) Assumes that the angular momentum of electrons is quantized

(b) Uses Faraday’s laws

(c) Predicts continuous emission spectra for atoms

(d) Predicts the same emission spectra for all types of atoms

 

Question 11:

Hydrogen atoms are excited from ground state to the state of principal quantum number 4. Then, what will be the number of spectral lines observed?

 

Question 12:

Give the number of electrons passing through a wire per minute. The current flowing through it is 500mA.

 

Question 13:

Why should electrostatic field be zero inside a conductor?

 

Question 14:

The emf of a cell is always greater than its terminal voltage. Why? Give reason.

 

Question 15:

Define the term ‘Mobility’ of charge carriers in a conductor. Write its S.I. unit.

 

Question 16:

Two inductors each of inductance ‘L’ are joined in parallel. What is their equivalent inductance?

 

Question 17:

Why does a metallic piece become very hot when it is surrounded by a coil carrying high frequency alternating current?

 

Question 18:

What is mutual Induction?

 

Question 19:

The vertical component of earth’s magnetic field at a place is  times the horizontal component. What is the value of angle of dip at this place?

 

Question 20:

State the reason, why GaAs is most commonly used in making of a solar cell.

 

SECTION - B

Question 21:

(a)In what respect is a toroid different from a solenoid? Draw and compare the pattern of the magnetic field lines in the two cases.
(b) How is the magnetic field inside a given’ solenoid made strong? 

 

Question 22:

The space between the plates of a parallel plate capacitor is completely filled in two ways. In the first case, it is filled with a slab of dielectric constant K. In the second case, it is filled with two slabs of equal thickness and dielectric constants K₁ and K₂ respectively as shown in the figure. The capacitance of the capacitor is same in the two cases. Obtain the relationship between K, K₁ and K₂.

 

Question 23:

Prove that a closed equipotential surface with no charge within itself must enclose an equipotential volume.

 

Question 24:

There are two sources of light, each emitting with a power of 100 W. One emits X-rays of wavelength 1nm and the other visible light at 500 nm. Find the ratio of a number of photons of X-rays to the photons of visible light of the given wavelength?

 

Question 25:

Show that for a material with refractive index µ ≥ 2, light incident at any angle shall be guided along a length perpendicular to the incident face.

 

Question 26:

Three identical bar magnets are riveted together at the centre in the same plane as shown in the figure. This system is placed at rest in a slowly varying magnetic field. It is found that the system of magnets does not show any motion. The north-south poles of one magnet are shown in the figure. Determine the poles of the remaining two.

OR

(a) Write two main observations of photoelectric effect experiment which could only be explained by Einstein’s photoelectric equation.

(b) Draw a graph showing variation of photocurrent with the anode potential of a photocell.

 

Question 27:

Explain the terms ‘depletion layer’ and ‘potential barrier’ in a p-n junction diode. How are the (a) width of depletion layer, and (b) value of potential barrier affected when the p-n junction is forward biased?

 

Question 28:

Draw the circuit diagram of a half wave rectifier and explain its working.

 

Question 29:

Draw a schematic arrangement of the Geiger-Marsden experiment. How did the scattering of α-particles by a thin foil of gold provide an important way to determine an upper limit on the size of the nucleus? Explain briefly.

 

Question 30:

A resistance R and a capacitor C are connected in series to a source V = V₀ sin wt. Find:

(a) The peak value of the voltage across the (i) resistance and (ii) capacitor.

(b) The phase difference between the applied voltage and current. Which of them is ahead?

 

Question 31:

A Zener of power rating 1 W is to be used as a voltage regulator. If Zener has a breakdown of 5V and it has to regulate voltage which fluctuated between 3V and 7V, what should be the value of Rs for safe operation in the figure?

 

Question 32:

Consider a 20 W bulb emitting light of wavelength 5000 A° and shining on a metal surface kept at a distance 2m. Assume that the metal surface has work function of 2 eV and that each atom on the metal surface can be treated as a circular disk of radius 1.5 A°.

(i) Estimate no. of photons emitted by the bulb per second. [Assume no other losses]

(ii) Will there be photoelectric emission?

(iii) How much time would be required by the atomic disk to receive energy equal to work function (2 eV)?

(iv) How many photons would atomic disk receive within time duration calculated in (iii) above?

(v) Can you explain how photoelectric effect was observed instantaneously?

 

Question 33:

The nucleus ²³⁵₉₂Y, initially at rest, decays into ²³¹₉₀X by emitting an a-particle

²³⁵₉₂Y               ²³¹₉₀X +⁴₂He +energy

The binding energies per nucleon of the parent nucleus, the daughter nucleus and a-particle are 7·8 MeV, 7·835 MeV and 7·07 MeV, respectively. Assuming the daughter nucleus to be formed in the unexcited state and neglecting its share in the energy of the reaction, find the speed of the emitted a-particle. (Mass of a-particle = 6·68 ´ 10^–27 kg)

 

Question 34:

A uniform conducting wire of length 12a and resistance R is wound up as a current-carrying coil in the shape of i) an equilateral triangle of side a; ii) a square if sides a. The coil is connected to a voltage source V₀. Find the magnetic moment of the coils in each case.

                                                                                                          

Section - D

Question 35:

(a)Using Gauss law, derive expression for electric field due to a spherical shell of uniform charge distribution s and radius R at a point lying at a distance x from the centre of shell, such that (i) 0 < x < R, and (ii) x > R.

(b)An electric field is uniform and acts along + x direction in the region of positive x. It is also uniform with the same magnitude but acts in – x direction in the region of negative x. The value of the field is E = 200 N/C for x > 0 and E = – 200 N/C 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 x-axis so that one flat face is at x = + 10 cm and the other is at x = – 10 cm. Find:

(i) The net outward flux through the cylinder.

(ii) The net charge present inside the cylinder.

OR

(a) Describe briefly, with the help of a circuit diagram, the method of measuring the internal resistance of a cell.

(b) Give reason why a potentiometer is preferred over a voltmeter for the measurement of emf of a cell.

(c) In the potentiometer circuit given below, calculate the balancing length l. Give reason, whether the circuit will work, if the driver cell of emf 5 V is replaced with a cell of 2 V, keeping all other factors constant.

 

Question 36:

(a) With the help of a labelled diagram, explain the working of a step-up transformer. Give reasons to explain the following:

(i) The core of the transformer is laminated.

(ii) Thick copper wire is used in windings.

(b) A conducting rod PQ of length 20 cm and resistance 0·1 W rests on two smooth parallel rails of negligible resistance AA¢ and CC¢. It can slide on the rails and the arrangement is positioned between the poles of a permanent magnet producing uniform magnetic field B = 0·4 T. The rails, the rod and the magnetic field are in three mutually perpendicular directions as shown in the figure. If the ends A and C of the rails are short circuited, find the

(i) external force required to move the rod with uniform velocity v = 10 cm/s, and

(ii) power required to do so.

OR

(a) Draw a labelled diagram of AC generator. Derive the expression for the instantaneous value of the emf induced in the coil.

(b)A circular coil of cross-sectional area 200 cm² and 20 turns is rotated about the vertical diameter with angular speed of 50 rad s^-1 in a uniform magnetic field of magnitude 3.0 x 10^-2 T. Calculate the maximum value of the current in the coil.

 

Question 37:

Draw the ray diagram of an astronomical telescope when the final image is formed at infinity. Write the expression for the resolving power of the telescope.

OR

Draw a labelled ray diagram to show image formation by a compound microscope and write the expression for its resolving power.

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