Class – XII
Subject Physics 2nd Paper(theoretical)
Time : 3 hrs. Marks.75
N.B. The figures in the right margin indicate full marks.)
1. (a) Establish the wheatstone bridge principle for the measurment of resistance by applying 6 kirchoff's laws.
(b) State the laws of resistance. 5
(c) 20c charge is given to a sphere of radius of 0.50 m. Find the electric potential at a
distance of 0.40m and 0.8m from the centre of the sphere.
Or, (a) Define electrochemical equivalent. Describe a method for the determination of 1+5=6
electrochemical equivalent of a substance by a voltameter.
(b) State and explain Faraday's laws of electrolysis. 5
(c) A galvanometer of resistance of 100W con safely pass 10 mA current. What arrangement is to be made so that 10A current can be measured by it?
2. (a) Establish the equation, 
for convex lens, here the symbols have their usual
for convex lens, here the symbols have their usual meaning. 6
(b) Describe with diagram the reason and remedy of short sight defect of vision. 5
(c) The refractive index of an equilateral prism is 
, find its angle of minimum deviation. 4
, find its angle of minimum deviation. 4Or, (a) What is called equivalent lens? Show that the power of an equivalent lens is equal to the
algebraic sum of the individual power of lenses. 1+5=6
(b) Derive the laws of reflection of light with the help of Huygen's wave theory of light. 5
(c) The phase difference between two points in a wave is 
. What is the path difference
. What is the path difference between those two points? 4
3. (a) Write Einstein's equation for the photoelectric effect and explain different terms in it. 6
(b) Derive the exponential law of radioactive decay. 5
(c) How long will it take to decay 40% of a piece of radon? Half life of radon is 3.82 days. 4
Or, (a) Derive the energy equation of electron of n-th orbit of hydrogen atom. 6
(b) Draw a circuit diagram fro a full wave rectifier using a diode and describe its working
principle.
(c) A particle is moving with velocity of 0.5 c. Determine the ratio of the mass at rest to the moving mass of the particle. 4
4. Derive the equation for the energy of a charged capacitor. 5
Or, What is called capacitance? The area of each plate of a parallel plate capacitor is 1.5 m2 and
the thickness of air between the plates is 1 mm. What is its capacitance?
5. State and explain the laws relating to production of heat in electric circuit. 5
Or, Define Faraday. A distribution line extended in east -west carries current of 60A. Calculate the
magnitude of magnetic field at a point 3m directly below the line. 1+4=5
6. What do you understand by self inductance? The voltage in the primary coil of a transformer is
10V and current flowing in it is 4 Amp. If the voltage in the secondary coil is 20 volt, find the
current in the secondary coil. 1+4=5
Or, What is a light year? The peak value of on alternating current is 7A. What is its root mean square
value? 1+4=5
7. Define optical centre. At what distance will an object be placed from a concave mirror of cocal
length of 12 cm so that the image becomes three times the size of the object? 1+4=5
Or, What is angle of minimum deviation? Mention its conditions. At what direction a fish inside
water is to look at in order to see the setting sun? [Refractive index, 
= 
]. 2+3=5
= ]. 2+3=58. What is threshold frequency? The work function of a material is 1.85 ev. What is its threshold
frequency? 1+4=5
Or, Write down four properties of X - rays. Calculate the final velocity achieved by an electron at
rest when it is passed through a potential difference of 10 kilo-volt. 2+3=5
9. Mention the fundamental postulates of Bhr's atom model. The decay constant of a radioactive
substance is 3.75 x 10-3 sec-1. Calculate its half life.
Or, What is called doping? If an electron mores with a velocity of 0.99c , what is its mass? 1+4=5
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