**Sub. Code: 210 ‘B’**

**NEB-GRADE XII**

**2076(2019)**

**Physics**

**Time: 3hrs Full Marks:75**

**Pass Marks: 27 (only for partial students)**

*Candidates are required to give their answers in their own words as far as practicable. The figure in the margin indicates full marks.***Group ‘A’**

1.
Answer in brief, any

**four**questions.**4x2=8**
a.
State the principle of potentiometer and write
down its one application.

b.
What is thermoelectric effect?

c.
Distinguish between ionic and electronic
conduction.

d.
An electron beam and a proton beam are moving
parallel to each other in the beginning. Do they always maintain this status?
Justify your answer.

e.
Define one ampere current in terms of force.

2.
Answer in brief, any

**four**questions.**4x2=8**
a.
Why discharge does not take place at very low
pressure?

b.
What do you mean by hole in semiconductor?

c.
Which has more energy – a photon in the
infrared or photon in the ultraviolet? Give reasons.

d.
All the radioactive series terminate at lead as
their final product. Why?

e.
What do you mean by greenhouse effect? Write
its effects.

f.
Does the universe have a centre? Explain.

3.
Answer in brief, any

**one**question.**2**
a.
Can longitudinal wave be polarized? Explain.

b.
An empty vessel sounds more than filled one
when it struck. Why?

4.
Answer in brief, any one question.

**2**
a.
State Huygen’s principle. Does it apply to
sound wave in air?

b.
Differentiate unpolarized and polarized light.

**Group ‘B’**

5.
Answer any

**three**questions.**3x4=12**
a.
What do you mean by shunt? Describe its use
converting a galvanometer into an ammeter.

b.
State Joule’s law of heating and verify it
experimentally.

c.
State Biot and Savart law. Derive an expression
for the magnetic field at a point due to a long straight conductor carrying
current.

d.
An alternating current passes through a circuit
containing an inductor and a resistor in series. Derive expression for the
current flowing and phase relation between the current and the voltage.

6.
Answer any

**three**questions.**3x4=12**
a.
What is quantization of charge? Describe the
theory of Millikan’s oil drop experiment to determine the number of charges on
an oil drop.

b.
What is P-N junction diode? Discuss its
application? Discuss its application as full wave rectifier.

c.
List out the laws of radioactive
disintegration. Deduce the expression N= Noe

^{Î»t}where symbols have their meaning.
d.
What are sources of energy? Discuss global
energy consumption pattern and demands.

7.
Answer any

**one**question.**4**
a.
Does the propagation of sound wave cause change
in thermodynamic condition of medium? Derive Laplace formula of velocity of
sound in air.

b.
What is Doppler’s effect? Derive an expression
for the apparent frequency received by a stationary observer when a source of
sound is moving away from the observer.

8.
Answer any

**one**question.**4**
a.
Describe Newton’s ring experiment and derive
expression for wavelength of light.

b.
Describe Foucault’s method of determining the
speed of light.

**Group ‘C’**

9.
Answer any

**two**numerical questions.**2x4=8**
a.
Two resistors of resistance 1000â„¦ and 2000â„¦ are
joined in series with a 100V supply. A voltmeter of internal resistance 40000â„¦
is connected to measure the potential difference across 1000â„¦ resistor.
Calculate the reading shown by the voltmeter.

b.
Two galvanometers, which are otherwise
identical, are fitted with different coils. One has a coil of 50 turns and
resistance 10â„¦ while the other has 500 turns and resistance of 600â„¦. What is
the ration of the deflection when each is connected in turns to a cell of e.m.f
25V and internal resistance 50â„¦?

c.
The magnetic flux passing perpendicular to the
plane of coil is given by passing perpendicular to the plane of coil is given
by Ã¸= 4t

^{2}+ 5t + 2 where Ã¸ is a weber and t is in second. Calculate the magnitude of instantaneous e.m.f induced in the coil when t=2 sec.
10. Answer
any

**two**numerical question.**2x4=8**
a.
An iron for which the charge per unit mass is
4. 40 x 10

^{7}c/kg has velocity of 3.52 x 10^{5}m/s and moves in a circular orbit in a magnetic field of flux density 0.4T. What will be the radius of this orbit?
b.
Obtain the de Broglie wavelength of neutron of
kinetic energy 150eV. (mass of neutron= 1.675 x 10

^{-27}kg. Planck’s constant= 6.6x 10^{–34}JS, 1eV= 1.6x10^{-19}J)
c.
Calculate the binding energy per nucleon of

_{26 }Fe^{56}. Atomic mass of_{26 }Fe^{56}is 55.9349*u*and that of_{1 }H^{1}is 1. 00783*u.*Mass of on^{1}=1.00867*u*and 1*u*= 931 MeV.
11.
A wire whose mass per unit length is 10

^{-3}kg/m is stretched by a load of 4 kg over the two bridges of a sonometer wire 1 m apart. It is struck at its middle point, what would be the wavelength and frequency of its fundamental vibration?
12.
How wide is the central diffraction peak on a
screen 5m behind a 0.01 mm slit illuminated by 500 nm light source?

**The End**

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