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Physics - 1998 ( I.S.C)
You are on Questions 6 to 13
SECTION -
B
Q 6.(a)
What is
meant by a 'wave front'? What is the shape of the wave front of a beam of
parallel waves?
State Huygens' principle and use it to describe the
process of reflection of a parallel beam of light incident on a plane
mirror obliquely, with the help of a labelled diagram. Prove that the
angle of incidence is equal to the angle of reflection.
(b)In a Fresnel biprism experiment, the fringe
width is found to be 0.5 mm when monochromatic source of wavelength 4000 A
is used. Keeping the distance between the source and the biprism constant
but reducing the distance between the source and the screen to half the
original value, the same biprism is used with a source of different
wavelength l. What is the value of l for this new setting
to produce fringes with fringe width 0-4 mm?
Q 7(a) Which plane is defined
as the plane of polarisation in a plane polarised electromagnetic
wave?
(b) The critical angle between
a given transparent medium and air is denoted by ic. A ray of
light in air medium enters this transparent medium at an angle of
incidence equal to the polarising angle(ip).Deduce a relation
for the angle of refraction(r) in terms of ic.
(c)A beam of paralled rays
makes normal incidence on a plane transmission diffraction grating and
coloured fringe lines are observed. The red line of the second order
spectrum overlaps exactly on the blue lineof the third order at an angle
of diffraction of 30°. If the wavelength of the red light is 7500 Å, What is the
wavelength of the overlapping blue colour? What is the number of lines
present per cm on the grating surface?
Q 8(a)
A liquid of refractive
index 1.5 is poured into a cylindrical jar of radius 20cm upto a height of
20 cm. A small bulb is lighted at the centre of the bottom of the
jar. Find the area of the liquid surface through which the light of
the bulb passes into air.
(b) Fig.7 shows a solid glass
sphere of radius 5 cm that has a amll air bubble (B) trapped at a distance
of 2 cm from the cnetre C. The refractive index of the mateiral of glass
is 1.5. Find the apparent position of the bubble where it will appear,
when seen through the surface of the sphere from an outside point E
Q 9(a) What is meant by the
term 'pure spectrum'?
Briefly describe a method to adjust the telescope
and collimeterof a spectrometer to set it for the production of a pure
spectrum.
(b)The focal lengths of the
eyepiece and objective of a compound microscope are 5 cm and 1 cm
respectively and the length of the tabe is 20 cm. Calculate the magnifying
power of this microsope when the final image is formed at infinity.
The value of least distance of distinct vision is 25 cm.
SECTION C
Q10 (a) With Reference to the
photoelectirc effect define the terms 'work function' and 'threshold
wavelength' for a given metal. On what factors will be following depends
during photoelectric emission from a metal surface :
(i) the magnitude
of photelectric current, and
(ii) the velocity of ejected dlectrons?
(b)In a certain
region of space a uniform electric field 7200 V/m and a uniform magnetic
field
1.8x10-3 T are simultaneouslypresents in mutually
perpendicular directions. An electron beam enters this region in a
direction perpendicular to both electric and magnetic fields. Calcuate the
velocity of elctrons in the beam if they pass through this region without
any deviation in their straight line path. if the electric field is now
switched off, what kind of path will be taken by the beam? Find the radius
of curvature of this path.(Mass of electron = 9x10-31kg and
Charge on electron = 1.6x10-19 C).
Q 11(a) 18 KV
accelerating voltage is applied across an X-ray tube. Calculate:
(i)The
velocity of the fastest electron striking the target,
(ii)The minimum
wavelength in the continuous spectrum of X-rays produced.(Mass of electron
= 9x10-31kg, Charge on electron = 1.6x10-19 C, h =
6.6x10-34 Js, c = 3x108 m/s).
(b) What are
Fraunhofer lines? Give a brief explanation for their occurence.
(c)
If a light wave
of wavelength 4950 Åis viewed as a continuous flow of photons what is the
energy in eV (values given for h,c,e etc. in Q.no 11(a) may be used).
Q 12(a) With the
help of labelled diagram explain the working of a Bainbridge Mass
Spectometer. Deduce an expression for the radius of curvature of the path
of an ion in terms of its mass number and charge. How is a linear
mass scale achieved for different isotopes?
(b) What is the purpose of (i)
moderator and (ii) controller in a nuclear reactor?
(c) Find out the binding energy per
nucleon of an a-particle
in MeV. It is given that the mases of a-particle, proton and neutron are respectively 4.00150 amu, 1.00728
amu and 1.00867 amu
Q 13.(a)
Distinguish between insulators, conductors and semiconductors in terms of
their energy band diagrams.
(b) Draw the current versus voltage
characteristic curve of Zener diode. Indicate the position of Zener
voltage. Draw a labelled circuit diagram of D.c voltage regulator using
Zener diode.
(c) What is the relation between
emitter current (IE), base current (IB)and collector
current (IC)at any instant in a properly baised common emitter
transistor circuit? Which one of the three has the smallest
magnitude?
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