# 12th physics question paper 2014 – bihar board

SECTION-A

Ultrashort Answer Type Questions

Answer any eight questions:

- What is the S.I. unit of electric dipole moment?
- Give two factors which affect capacitance of a conductor.
- Write down two characteristics of fuse wire.
- What is the material of optical fiber core?
- Write down the expression of fringe width of interference.
- What is inductive reactance?
- State Brewster’s law.
- Define stopping potential.
- Give the symbol of NAND gate.
- What is ionosphere?

SECTION-B

Very Short Answer Type Questions

Answer any ten questions:

- Why do electric lines of force never intersect each other? Can two equipotential surfaces intersects?
- A wire of resistivity p is stretched to double its length. What will be its new resistivity?
- State two characteristics properties distinguishing the behaviors of paramagnetic and diamagnetic materials.
- Find an expression of self induction of an ideal solenoid.
- What is transformer? What is transformation ratio?
- What is the importance of radial magnetic field in a moving coil galvanometer?
- What is electrostatic shielding? Give one of its practical applications.
- Write down the equation of induced current at any instant in L-C-R circuit when XL > XC or circuit is inductive.
- Out of electric field vector and magnetic field vector in an electromagnetic wave, which is more effective and why?
- What are the (A) momentum, (B) de Broglie wavelength of an electron with kinetic energy of 120 eV?
- What happens when a forward bias is applied to a p-n junction?
- Why a longitudinal wave cannot be polarized?

- What are the utilities of moderator, coolant and controlling rods with references to nuclear reactor?
- What are base band, bandwidth and fading?
- Draw the voltage-current characteristic curve of a diode and mark its important parameter.
- Define threshold frequency, word function and stopping potential with references to photoelectric effect.
- For an amplitude modulated wave, the maximum amplitude is found to be 10V while the minimum amplitude is found be 2V. Determine the modulation index µ.
- Double convex lenses are to be manufactured from a glass of refractive index 1.55 with both faces of the same radius of curvature. What is the radius of curvature required if the focal length is to be 20cm?
- Name the factors responsible for decreasing the efficiency of a transformer.
- Write the truth table for a NAND Gage connected in the given figure and identify the exact logic operation carried out by this circuit.
- An electric bulb is rated 100W for 220V a.c. supply of 50Hz. Calculate (i) the resistance of the bulb (ii) the r.m.s. current through the bulb.
- Mention three difference modes of propagation used in communication system.
- Determine the potentials at the points X1 and X2 in the circuit.
- Derive an expression for the torque experienced by electric dipole in external electric field.

SECTION-D

Long Answer Type Questions

Answer any three questions:

- State the underlying principles of a transistor being used as an oscillating circuit. Draw a circuit diagram showing how the feedback is accomplished by inductive capacitance. Explain oscillator action.
- What is the photoelectric emission effect? What are the laws of photoelectric emission effect? How did Einstein explain the observed fact of photoelectric effect?
- Define wave front and secondary wavelets. Verify laws of reflection or laws of refraction on the basis of Huygens wave theory.
- (a) An angular magnification of 30X is desired using an objective of focal length 1.25 cm and an eyepiece of focal length 5cm. How will you set up the compound microscope?

(b) You are given two circuits as shown in figure, which consists of NAND gate. Identify the logic operation carried out by the two circuits.

- Apply Gauss theorem to find the electric field in a point near charged conductor.

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