(i) All questions are compulsory.

(ii) There are 30 questions in total. Question Nos. 1 to 8 are very short answer type questions and carry one mark each.

(iii) Question Nos. 9 to 18 carry two marks each, question 19 to 27 carry three marks each and question 28 to 30 carry five marks each.

(iii) There is no overall choice. However, an internal choice has been provided in one question of two marks; one question of three marks and all three questions of five marks each. You have to attempt only one of the choice in such questions.

(iv) Use of calculators is not permitted.

Q1 :

State two characteristic properties of nuclear force.

**Answer :**

Properties of nuclear force:

(i) Nuclear force is the strongest force in nature.

(ii) Nuclear force is only effective on a very short range.

Q2 :

How does the angle of minimum deviation of a glass prism vary, if the incident violet light is replaced with red light?

**Answer :**

Î´_{violet}> Î´_{red}

Thus, when incident violet light is replaced with red light, the angle of minimum deviation of a glass decreases.

Q3 :

The instantaneous current and voltage of an a.c. circuit are given by

*i*= 10 sin
300 *t*A and

*V*= 200 sin
300 *t*V.

What is the power dissipation in the circuit?

**Answer :**

It is given that:

*i*= 10 sin
300 *t*A

*V*= 200 sin
300 *t*V

âˆ´ *i*_{0}= 10 A and *V*_{0}= 200 V

âˆ´ Average power dissipation
= *V*_{0}*i*_{0}

= 200 Ã—10 = 2000 W

Q4 :

Why should the spring/suspension wire in a moving coil galvanometer have low torsional constant?

**Answer :**

Q5 :

Why does the bluish colour predominate in a clear sky?

**Answer :**

Q6 :

Which orientation of an electric dipole in a uniform electric field would correspond to stable equilibrium?

**Answer :**

Q7 :

Two lines, *A*and *B*, in the plot given below show the
variation of de Broglie wavelength, Î»versus, where
*V* is the
accelerating potential difference, for two particles carrying the
same charge.

Which one of two represents a particle of smaller mass?

**Answer :**

Q8 :

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

**Answer :**

Q9 :

Draw a labelled ray diagram of an astronomical telescope in the near point position. Write the expression for its magnifying power.

**Answer :**

Q10 :

The following figure shows the variation of
intensity of magnetisation versus the applied magnetic field
intensity, *H*_{j}for two magnetic materials A and
B:

(a) Identify the materials A and B.

(b) Why does the material B have a larger susceptibility than A for a given field at constant temperature?

**Answer :**

Q11 :

Two metallic wires of the same material have the same length but cross-sectional area is in the ratio 1:2. They are connected (i) in series and (ii) in parallel. Compare the drift velocities of electrons in the two wires in both the cases (i) and (ii).

**Answer :**

Q12 :

Draw a block diagram of a simple amplitude modulation. Explain briefly how amplitude modulation is achieved.

**Answer :**

Q13 :

Calculate the energy released in MeV in the following nuclear reaction:

[Mass of

Mass of

Mass of

1u = 931.5 MeV/c^{2}]

**Answer :**

Q14 :

Using Ampere”™s circuital law,
obtain an expression for the magnetic field along the axes of a
current carrying solenoid of length *l*and having
*N* number of
turns.

**Answer :**

Q15 :

Derive an expression for the resistivity of a good conductor, in terms of the relaxation time of electrons.

**Answer :**

Q16 :

The circuit arrangement given below shows that when an a.c. passes through the coil A, the current starts flowing in the coil B.

(i) State the underlying principle involved.

(ii) Mention two factors on which the current produced in the coil B depends.

**Answer :**

Q17 :

State one feature by which the phenomenon of interference can be distinguished from that of diffraction.

A parallel beam of light of wavelength 600 nm is
incident normally on a slit of width
“*a*”™. If the
distance between the slits and the screen is 0.8 m and the
distance of 2^{nd}order maximum from the centre of
the screen is 15 mm, calculate the width of the slit.

**Answer :**

Q18 :

Two point charges *q*_{1}= 10 Ã—10^{−8} C and *q*_{2}= −2
Ã—10^{−8}C are
separated by a distance of 60 cm in air.

(i) Find at what distance from the
1^{st}charge, *q*_{1}, would the electric potential be
zero.

(ii) Also calculate the electrostatic potential energy of the system.

**OR**

Two point charges 4*Q*, *Q* are separated by 1 m in air. At
what point on the line joining the charges is the electric field
intensity zero? Also calculate the electrostatic potential energy
of the system of charges, taking the value of charge,
*Q*= 2
Ã—10^{−7}C.

**Answer :**

Q19 :

Identify the following electromagnetic radiations as per the wavelengths given below. Write one application of each.

(a) 10^{−3}nm

(b) 10^{−3}m

(c) 1 nm

**Answer :**

Q20 :

Explain why high frequency carrier waves are needed for effective transmission of signal. A message signal of 12 KHz and peak voltage 20 V is used to modulate a carrier wave of frequency 12 MHz and peak voltage 30 V. Calculate the (i) modulation index (ii) side-band frequencies.

**Answer :**

Q21 :

Distinguish between unpolarised and plane polarised light. An unpolarised light is incident on the boundary between two transparent media. State the condition when the reflected wave is totally plane polarised. Find out the expression for the angle of incidence in this case.

**Answer :**

Q22 :

Draw the labelled circuit diagram of a common-emitter transistor amplifier. Explain clearly how the input and output signals are in opposite phase.

**OR**

State briefly the underlying principle of a transistor oscillator. Draw a circuit diagram showing how the feedback is accomplished by inductive coupling. Explain the oscillator action.

**Answer :**

Q23 :

The ground state energy of hydrogen atom is − 13.6 eV.

(i) What is the kinetic energy of an electron in
the 2^{nd}excited state?

(ii) If the electron jumps to the ground state
from the 2^{nd}excited state, calculate the
wavelength of the spectral line emitted.

**Answer :**

Q24 :

The following graph shows the variation of stopping potential *V*_{0}with the frequency
Î½of the
incident radiation for two photosensitive metals X and Y:

(i) Which of the metals has larger threshold wavelength? Give reason.

(ii) Explain giving reason, which metal gives out electrons, having larger kinetic energy, for the same wavelength of the incident radiation.

(iii) If the distance between the light source and metal X is halved, how will the kinetic energy of electrons emitted from it change? Give reason

**Answer :**

Q25 :

A circular coil of 200 turns and radius 10 cm is placed in a uniform magnetic field of 0.5 T, normal to the plane of the coil. If the current in the coil is 3.0 A, calculate the

(a) Total torque on the coil

(b) Total force on the coil

(c) Average force on each electron in the coil due to the magnetic field

Assume the area of cross-section of the wire to be
10^{−5} m^{2}and the free electron density is
10^{29}/m^{3}.

**Answer :**

Q26 :

The inputs *A*and *B* are inverted by using two NOT
gates and their outputs are fed to the NOR gate as shown
below.

Analyze the action of the gates (1) and (2) and identify the logic gate of the complete circuit so obtained. Give its symbol and the truth table.

**Answer :**

Q27 :

(i) Calculate the equivalent resistance of the
given electrical network between points *A*and *B*.

(ii) Also calculate the current through
*CD*and
*ACB*, if a 10
V d.c source is connected between *A*and *B*, and the value of
*R*is assumed
as 2 Î©.

**Answer :**

Q28 :

Derive an expression for the energy stored in a parallel plate capacitor.

On charging a parallel plate capacitor to a
potential*V*, the spacing between the plates is
halved, and a dielectric medium of is introduced between
the plates, without disconnecting the d.c source. Explain, using
suitable expressions, how the (i) capacitance, (ii) electric
field and (iii) energy density of the capacitor charge.

**OR**

(a) Define electric flux. Write its SI unit.

(b) The electric field components due to a charge inside the cube of side 0.1 m are as shown:

Where Î± = 500 N/C - m

*E*_{y}= 0, *E*_{z}= 0

Calculate (i) the flux through the cube and (ii) the charge inside the cube

**Answer :**

Q29 :

Derive the lens formula, for a concave lens, using the necessary ray diagram.

Two lenses of powers 10 D and - 5 D are placed in contact.

(i) Calculate the power of the new lens.

(ii) Where should an object be held from the lens, so as to obtain a virtual image of magnification 2?

**OR**

(a) What are coherent sources of light? Two slits in Young’s double slit experiment are illuminated by two different sodium lamps emitting light of the same wavelength. Why is no interference pattern observed?

(b) Obtain the condition for getting dark and bright fringes in Young’s experiment. Hence write the expression for the fringe width.

(c) If *S*is the size of the source and its
distance from the plane of the two slits, what should be the
criterion for the interference fringes to be seen?

**Answer :**

Q30 :

An a.c source generating a voltage
is connected to a
capacitor of capacitance *C*. Find the expression for the
current *i*, flowing through it, plot a graph
of *v*and *i*versus *Ï‰**t*to show that the current is
, ahead of the
voltage.

A resistor of 200 Î©and a capacitor of 15
Î¼F are connected
in series to a 220 V, 50 Hz a.c source. Calculate the current in
the circuit and the *rms*voltage across the resistor and
the capacitor. Is the algebraic sum of these voltages more than
the source voltage? If yes, resolve the paradox.

**OR**

Explain briefly, with the help of a labelled diagram, the basic principle of the working of an a.c generator.

In an a.c generator, coil of *N*turns and area
*A*is rotated
at *V*revolutions per second in a uniform magnetic field
*B*.

Write the expression for the *emf*produced. A 100-turn
coil of area 0.1 m^{2}rotates at half a revolution per
second. It is placed in a magnetic field 0.01 T perpendicular to
the axis of rotation of the coil. Calculate the maximum voltage
generated in the coil.

**Answer :**

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