Full marks: 70

Group-B

Answer the following question in short :[2x5=10]

1. A silver wire has a resistance of 2.1 ohms at $27.5^0 C$ and a resistance of 2.7 ohms at $100^0 C$. Determine the temperature coefficient of the resistivity of silver.
                    OR
Length, diameter, and specific resistance of materials of two wires are each in the ratio 2:1. the resistance of a longer wire is R. find the resistance of the other wire.

2. The value of the magnetic field at a distance of 1 meter from a long straight conductor is $10^{-7} T$. what is the value of the current following through the wire?
                   OR
Define the angle of declination and magnetic permeability.

3. State five electromagnetic waves and arrange them in the increasing order of their penetrating power.
                 OR
State four properties of electromagnetic waves.

4. State ampere's circuital law modified by maxwell.
                   OR
What is wattless current? What are eddy currents?

5. Write the relation between drift velocity and electric field. what is the effect on the drift velocity of electrons, if an electric field is increased?
                  OR
Establish a relation between electric current and drift velocity.

Group-C

Answer the following question in short:  [3x9=27]

6. Define dipole moment with the unit. Find an expression for the electric field strength at a distant point along an electric dipole's equatorial line.
                OR
What is the quantization of charge? Two-point charges of +1$\mu c$ and -4$\mu c$  are separated by a distance of 4cm. Find the point on the line joining them at which the electric field intensity is zero.

7. Derive an expression for the potential energy of an electric dipole of dipole moment $\vec{P}$ in an electric field $\vec{E}$
            OR
write the dimension of capacitance. A capacitor of the capacitance of 20$\mu F$ is connected with a 20 V supply. Another 5$\mu F$ capacitor is now connected in parallel with the first. Find the p.d. across the combination.

8. State and explain Biot-Savart law and hence define 1 emu current.
                OR
Define electric flux. The magnetic moment of a steel wire of length 'L' is 'M'. the wire is bent in the form of a semicircle. Find the magnetic moment of this semicircular wire.

9. What are coherent sources? In a double-slit experiment with monochromatic light, fringes are obtained on a screen placed at some distance from the slit. If the screen is moved 5 cm towards the slit, the change in fringe width is $3\times10^{-3}$cm. if the distance between the slit is 1 mm. Calculate the wavelength of light used.
                    OR
Define the term 'dispersion by prism' and give the reason for its occurrence. How the defect of myopia in the human eye can be corrected?

10. State Huygen's principle. using it to verify Snell's law of refraction.
                OR
What do you mean by the interference of light? Write two essential conditions for a sustained interference pattern to be produced on screen.

11. Derive the lens formula $\frac{1}{f}=\frac{1}{v}-\frac{1}{u}$ of a concave lens, using necessary ray diagram.
                OR
Describe an astronomical telescope and find an expression for its magnifying power.

12. Explain 'stopping potential' and 'work function'. Write down einstein's photoelectric equation and explain the terms used.
            OR
What is meant by a de-Broglie wave? Find the expression for the wavelength of the de-Broglie wave associated with an electron accelerated from rest through a potential difference 'V' Volt.

13. Draw the current versus voltage characteristic curve of a zener diode indicating the position of Zener voltage. Draw a labeled diagram of a DC voltage regulator using a Zener diode and explain the load regulation process.
                OR
Draw the circuit diagram to show the use of a transistor as an oscillator. State how the positive feedback is provided in the circuit.

14. Define the half-life of a radioactive substance. Establish its relation with the decay constant.
            OR
Derive an expression for the average life of radio nuclei. Give its relationship with half-life.

Group-D

Answer the following questions [5x3=15]

15. a)  A battery is made up of m rows of cells, with n cells in each row. the cells have identical e.m.f 'e' and internal resistance 'r'. Find the current 'i' which is delivered to an external circuit having resistance R. Obtain the condition when the current is maximum.
b) Three bulbs 30W, 60 W, and 100 W are connected to 220 V mains. If bulbs are connected in series, which one will glow most brightly and why?
        OR
a) What is Wheatstone bridge?
b) Obtain its balance condition.
c) Define emf and terminal p.d. of a cell

16. a) Derive the construction and working principle of a moving coil galvanometer. Derive the necessary formula.
        OR
a) How will you convert a galvanometer into a voltmeter? What will be the resistance of the ammeter formed?
b) What is the effect of temperature on diamagnetic, paramagnetic, and ferromagnetic substances? Explain

17). a) Draw a schematic diagram of a reflecting telescope (Cassegrain). write two important advantages that a reflecting telescope has over a refracting telescope.
b) What are optical fibers? Mention their one practical application.
            OR
a) What is diffraction?
b) Derive an expression for the angular spread of central maxima in the single slit diffraction pattern.
c) Define the term 'wavefront'.