# 12th physics question paper 2015 – bihar board

Section – I (Objective Type)

- The electric dipole moment of an electric dipole made up of two opposite charges having magnitude + 3.2 x 10-19+C and -3.2 x 10-19C separated by a distance 2.4 x 10-10m is

(a) 7.68 x 10-27 C-m (b) 7.68 x 10-29 C-m

(c) 7.86 x 10-29 C-m (d) 7.86 x 10-27 C-m

- 64 Identical drops each of capacity 5µF combine to form a big drop. What is the capacity of big drip?

(a) 164µF (b) 20µF

(c) 4 µF (d) 25 µF

- Kilowatt-hour (kWh) is the unit of

(a) energy (b) power

(c) torque (d) force

- The algebraic sum of all currents meeting at any point in an electrical circuit is

(a) Infinite (b) Positive

(c) Zero (d) Negative

- Dimension of permeability is

(a) MLT-2I-2 (b) MLT2I-2

(c) MLT-2I 2 (d) MLT-2I

- Impedance of L-R circuit

(a) (b)

(c) (d)

- The direction of propagation of electromagnetic wave is

(a) Parallel to (b) Parallel to

(c) Parallel to (d) Parallel to

- When a ray of light enters a glass slab, its wavelength

(a) Increases (b) Decreases

(c) Remains unchanged (d) Data are not complete

- The value of amplifier modulation index is

(a) always 0 (b) between 1 and ∞

(c) between 0 and 1 (d) always ∞

- Boolean expression of NOR gate is

(a) A + B = Y (b)

(c) A . B = Y (d)

- The intensity of electricity filed at any point on the surface of a charged conductor is

(a) zero (b) perpendicular to the surface

(c) tangential to the surface (d) at 450 to the surface

- Permittivity of free space is

(a) 9 x 109 mF-1 (b) 1.6 x 1019 C

(c) 8.85 x 10-12 Fm-1 (d) 8.85 x 10-9 Fm-1

- Power of electric circuit is

(a) V . R (b) V2 . R

(c) (d) V2 . R . I

- Electron volt (eV) is the measure of

(a) charge (b) potential difference

(c) current (d) energy

- Lens law is associated with

(a) charge

(b) mass

(c) energy

(d) principle of conservation of momentum

- The final image in astronomical telescope is

(a) real and erect (b) real and inverted

(c) virtual and inverted (d) virtual and erect

- When two converging lenses of same focal length are placed in contact, then the focal length of the combination is

(a) (b) 2

(c) (d) 3

- The transverse nature of light wave supports

(a) interference (b) reflection

(c) polarisation (d) dispersion

- The colour of a thin film is due to

(a) scattering (b) interference

(c) dispersion (d) diffraction

- If ɸ is the phase difference between ac current and e.m.f., then the value of power factor is

(a) tan ɸ (b) cos2 ɸ

(c) sin ɸ (d) cos ɸ

- Unit of self-induction is

(a) Weber (b) Ohm

(c) Henry (d) Gauss

- The working of dynamo is based on the principle of

(a) hearing effect of current (b) electromagnetic induction

(c) magnetic induction (d) electric induction

- The equation of an ac is represented by I = 0.6sin 100 . The frequency of ac is

(a) 50 (b) 50

(c) 100 (d) 100

- Nickel is

(a) diamagnetic (b) paramagnetic

(c) ferromagnetic (d) none of these

- Brewster’s law is

(a) (b)

(c) (d)

- With the increase of temperature, the resistance of a semiconductor

(a) increases

(b) decreases

(c) sometimes increases and sometimes decreases

(d) remains unchanged

- The ratio of peak value and r.m.s. value of ac is

(a) 2 (b)

(c) (d)

- Which frequency range is used for TV transmission?

(a) 30-300 Hz (b) 30-300 KHz

(c) 30-300 MHz (d) 30-300 GHz

Section – II (Non- Objective Type)

- Define electric dipole moment and write its SI units.
- Write two main features of Laser rays.
- What is the function of second plate in a parallel plate capacitor?
- Write two uses of shunt.12th physics question paper 2016 – Bihar board
- The charge on a metallic sphere of radius 9cm is 4x10-6 C. Calculate the potential energy of charge on the conductor.
- When two resistors are connected in series and parallel, then their equivalent resistances are 16Ω and 3 Ω respectively. Find out the resistance of each resistor.
- Name the energy losses in a transformer.
- The equation of an ac is I=20sin 200 . Find out the frequency, peak value and r.m.s. value of the current.
- Tow thin lenses of powers 5D and 2D are placed coaxially at a distance 20cm apart. Find the focal length and power of the combination of lenses.
- Distinguish between n-type and p-type semiconductors.
- Define modulation. Write its types.

Long Answer Type Questions

- Define electric intensity. Derive an expression for electric intensity at a point suited pm the axis of electric dipole.

Or

Define electric flux. State and prove Gauss theorem.

- Establish the formula

Or

Write Huygens principles of light wave. Prove the laws of reflection or refraction of light on the basis of Huygens principles of light wave.

- Explain Biot-Savart law. With its help derive an expression for the magnetic field at any point on the axis of a current carrying circular loop.

Or

Define Kirchhoff’s laws of electric circuit. Derive an expression for a balanced. Wheat stone’s bridge using Kirchhoff’s law.

- Give postulates of Bohr’s theory. Explain hydrogen spectrum on the basis of Bohr’s theory.

Or

Write down Einstein’s photoelectric equation and explain the photoelectric effect on its basis.

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