**CLASS XII – SAMPLE PAPER**

## PHYSICS

Time allowed : 3 hours

Max. Marks : 70

**General Instructions:***All questions are compulsory**There are 30 questions in total. Questions 1 to 8 carry one mark each, 9 to 18 carry two marks each, 19 to 27 carry 3 marks each and 28 to 30 carry 5 marks each.**There is no overall choice, but internal choices are provided. You have to attempt only one choice in full.**Use of calculator is not permitted.**You may use the logarithm table, if required.*

1. Express dielectric constant in terms of capacitance.

2. What is magnetic susceptibility?

3. Define electromagnetic induction.

4. Give the relation between the magnitudes of electric and magnetic field vectors in an electromagnetic wave.

5. What happens to the interference pattern if the phase difference between two sources continuously vary?

6. What is stopping potential?

7. Identify the logic operation performed by the following combination of gates.

8. What is doping?

9. A regular hexagon of side 10cm has a charge 5µ C at each of its vertices. Calculate the potential at the centre of the hexagon.

10. In the given circuit, a potential difference of 3V is required between A and B. Calculate the value of R

_{1}.

11. Distinguish between emf and potential difference.

12. Explain briefly with equation, how a galvanometer is converted into a voltmeter.

13. A coil of inductance 0.5H and resistance 100 ohm are connected to 220V, 50Hz ac supply. i) What is the maximum current in the coil? ii) What is the time lag between voltage maximum and current maximum?

14.

A bulb and an ac source are connected to an inductance coil through a key as shown in figure. The switch is closed and after some time an iron rod is inserted into the coil. What happens to the glow of the bulb? Give reason.

OR

Two identical rectangular loops 1 and 2 are placed along with a straight, long current carrying conductor between them. When they are pulled away from the conductor with the same velocity, will the emf induced in them be equal? Why?

- Why is it necessary to use satellites for long distance TV transmission?
- Using the data given below, state which of the given lenses will you use an eye piece and an objective to construct an astronomical telescope.

Lens | Power | Aperture |

L1 | 3D | 8cm |

L2 | 6D | 1cm |

L3 | 10D | 1cm |

- A transistor has a current amplification factor of 50. In a common emitter amplifier circuit, collector resistance is taken as 5kΩ and input resistance as 1kΩ. Calculate the output voltage if the input voltage is 0.01V.
- What are carrier waves ? Why should transmitters use different carrier frequencies for transmitting from different stations?.
- With the help of a circuit diagram, explain how the value of an unknown resistance is determined using a metrebridge.
- What is Q- factor ? Show that the Q- factor for a series LCR circuit is ω
_{0}L/R.

OR

Derive an expression for the power consumed by a series LCR circuit. Hence define power factor.

- Two polaroids are kept crossed to each other and one of them is rotated through 60
^{0}. What percentage of incident unpolarized light will pass through the system? - With the help of suitable ray diagram explain the formation of primary rainbow.
- Show that De Broglie’s hypothesis is in accordance with Bohr’s quantum condition.
- Derive an expression for the radius of an electron in the n
^{th}orbit of a hydrogen atom.

25. Uranium 238 emits a proton according to the following reaction. .U Pa + H

Calculate the energy associated with this reaction. Is it a spontaneous reaction ? Why?

( U = 238.05079U, H = 1.000783U, Pa = 237.05121 U )

- What is a Zener diode? Briefly explain the working of a Zener diode as a Voltage regulator.
- What is amplitude modulation? Show the various stages of an AM receiver using a block diagram.
- State Gauss’ theorem in electrostatics. Give the mathematical expression.

Using Gauss’ theorem, derive an expression for the electric field at a point due to an infinite plane sheet of charge. OR

i) Define capacitance.

ii) Derive an expression for the capacitance of a parallel plate capacitor.

iii) Derive an expression for the capacitance when a dielectric slab whose thickness is less than the separation between the plates is introduced between the plates.

- i) Explain the principle, construction and working of a cyclotron.

ii) Derive expressions for the cyclotron frequency and the kinetic energy of the ions. OR

i) State Ampere’s circuital law.

ii) Use it to determine the magnetic field at a point a) outside and b) inside an infinitely long current carrying conductor.

- i) What are coherent sources?

ii) Explain Young’s double slit experiment.

iii) Derive an expression for the fringe width. OR

i) Derive an expression for the refractive index of the material of a prism.

ii) An equilateral prism made up of a material of refractive index 1.52 is kept in water of refractive index 1.33. what is the angle of minimum deviation?

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