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**Group 'A'**

a. The sound produced in the air is not heard by a person deep inside the water. Why?

4. Answer in brief: (anyone) [1x2 = 2]

a. With which color of light can a Hubble space telescope see finer detail in a distant astronomical object: red, blue, or UV-rays? Explain your answer.

b. Two polaroids are placed with their transmission axis at 90^{0} to each other and the transmitted intensity of light is zero. What happens in the intensity if one more Polaroid is placed in between them, bisecting the angle between them?

6. Answer in detail: (any three) [3x4 = 12]

a. Discuss the law of photoelectric effect. How Einstein's law of photoelectric effect can be verified by using Millikan's experiment.

7. Answer in detail: (anyone) [1x4 = 4]

a. Write Newton's formula of the velocity of sound in air. Discuss how Laplace corrected Newton's formula.

8. Answer in detail: (anyone) [1x4 = 4]

a. State Huygen's principle. Discuss how the Huygen's principle can be used to verify the laws of reflection of light.

b. Define diffraction of light. Explain Fraunhofer's diffraction at a single slit.

9. Solve the following: (any two) [2x4 = 8]

a. A coil inductance 0.50H and resistance 100Ω is connected to a 240 V, 50 Hz AC supply. (a) What is the maximum current in the coil? (b) What is the time lag between the voltage maximum and the current maximum?**b. **A battery has an emf of 15.0 V. The terminal voltage of the battery is 11.6 V when it is delivering 20.0 W power to an external load resistor of R. (a) What is the value of R? (b) What is the internal resistance of the battery?**c. **An electromagnet produces a magnetic field of 0.55T in a cylindrical region of radius 2.5cm between its poles. A straight wire carrying a current of 10.8A passes through the center of this region and is perpendicular to both the axes of the cylindrical region and the magnetic field. What magnetic force is exerted on the wire?

10. Solve the following: (any two) [2x4 = 8]

a. An electron beam after being accelerated from rest through the potential difference of 5KV in a vacuum is allowed to impinge normally on a fixed surface. If the incident current is 50μA, determine the force exerted on the surface assuming that it brings the electron to rest. Take the mass of an electron is 90.1x10^{-31} kg.**b. **It is proposed to use nuclear fusion _{1}H^{2} + _{1}H^{2} → _{2}He^{4} in a nuclear reactor of 200MW rating. It the energy from the above reaction is used with 25% efficiency in the reactor, how many grams of the deuterium will be needed per day. The mass of _{1}H^{2} and _{2}He^{4} are 2.0140 amu and 4.0026 amu respectively.**c. **An electron of energy 20eV comes into collision with a hydrogen atom in the ground state. The atom excited to a higher state and the electron is scattered with reduced velocity. The atom subsequently returns to the ground state with the emission of a photon of wavelength 1.216x10^{-7}m. Determine the velocity of scattered electron.

**11. **A boy is sitting on a swing which is moving to an angle of 30^{0} from the vertical is blowing a whistle which has a frequency of 1kHz. The whistle is 2m from the point of support of the swing. A girl stands in front of the swing. Calculate the maximum and minimum frequency of the sound she will hear. (take the velocity of sound=330m/s and g=9.8m/s^{2 }) **[4]**

**12. **In an experiment using Young's double-slit experiment, the distance between the center of the interference patterns and the tenth bright fringe on either side is 3.44cm. The distance between the slit and the screen is 2m. If the wavelength of the light used is 5.89x10^{-7}m, determine the slit separation and angle made by central bright fringe at the slit. [4]

**Source: **Department of Physics, St. Xavier's College, Maitighar.

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