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Physics
Class-
XII 1999(CBSE)
You are on Set no 1 Qno. 21
to 30
Q21) State Faraday's laws of electrolysis. Write down
the relation connecting chemical equivalent and electro-chemical
equivalent. (Marks 3)
Q22) An electron is moving at 106m/s in a
direction parallel to a current of 5 A, flowing through an
infinitely long straight wire, separated by a perpendicular distance
of 10 cm in air. Calculate the magnitude of the force experienced by
the electrons. (Marks 3)
Q23) A bar magnet, held horizontally, is set into
angular oscillations in Earth's magnetic field. It has time periods
T1 and T2 at two place, where the angles of
dip are  1 and 2 respectively.
Deduce an expression for the ratio of the resulting magnetic field
at the two places. (Marks 3)
Q24) Verify Snell's law of refraction using Huygens'
wave theory. (Marks 3)
Q25) Find the position
of an object which when placed in front of a concave mirror or focal
length 20 cm, produces a virtual image, which is twice the size of
the object. (Marks 3)
Q26) If the frequency of the incident radiation on the
cathode of a photo cell is doubled, how will the following change
:
(i) Kinetic energy of the electrons,
(ii) Photoelectric
current,
(iii) Stopping potential.
Justify you answer.
(Marks 3)
Q27) Explain, with the help of a circuit diagram, why
the output voltage is out of phase with the input voltage in a
common emitter transistor amplifier. (Marks 3)
Q28) With the help of a labelled diagram, describe
Millikan's oil-drop experiment for determining the charge of an
electron. (Marks 5)
Q29) Draw the curves showing the variation of inductive
reactance and capacitive reactance with applied frequency of an a.c
source.
A capacitor, a resistor of 5  , and an inductor of 50 mH are
in series with an a.c. source marked 100 V, 50 Hz. It is found that
voltage is in phase with the current. Calculate the capacitance of
the capacitor and the impedance of the circuit. (Marks
2+3)
Q30) Define capacitance of a capacitor. Give its unit.
Derive an expression for the capacitance of a parallel plate
capacitor in which a dielectric medium of dielectric constant K
fills the space between the plates.
OR
Explain the principle,
construction and working of a Van de Graaff generator. (Marks 5)
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