## CBSE MODEL TEST PAPER 2009 - 2010

TIME: THREE HOURS XII  PHYSICS M. M. 70
Q.1 With the help of a neat labelled diagram explain the principle and working of moving coil
galvanometer. What is the function of (i) Uniform radial field (ii) Soft iron core in such device.
OR
(i) Using Biot Savart law derive an expression for magnetic field due to a current carrying loop at a point along the axis of loop.
(ii) A long straight wire of a circular cross section of radius r carrying study current I which is uniformly distributed across this cross section. Calculate the magnetic field in region R>r and RQ.2 (a) Using the relation for refraction at a single spherical refracting surface derive the lens maker formula.
(b) Aconvex lens of focal length 0.2 m and made of glass (μ=1.50) is immersed in water (μ=1.33). Find the change in focal length of the lens.
(c) How is the focal length of a spherical mirror affected, when the wave length of the light used is increased ?
OR
(a) Using Huygens principle explain the refraction of a plane wave front at a plane surface.
Hence prove Snells law.
(b) Write to conditions of total internal reflection.
(c) An object is placed in front of a convex mirror of focal length 30 cm. if the image formed is quarter of the size of object. Find the position of the image

Q.3 (a) Why does a metallic piece becomes very hot when it is surrounding by a coil carrying high frequency alternating current?
(b) Steel is preferred for making electromagnets. Give one reason.
Q.4 Electromagnetic radiations with wave length
(i) λ1 are used to kill germs in water purifiers
(ii) λ2 are used in TV communication system
(iii) λ3 play an important role in maintaining the earths warmth.
Name the part of the electro magnetic spectrum to which these radiations belong. Arrange these wavelength in decreasing order of there magnitude.
Q.5What the effect on the interference fringes in youngs double slit experiment, if
(i) The separation between the slits Is halved and
(ii) Entire apparatus is immersed in liquid of refractive index μ. And show the interference pattern on the screen.
Q.6Why are photodiodes used preferable in reverse bias condition? A photodiode is fabricated from a semiconductor with band gap of 2.8 eV. Can id detect a wave length of 6000 nm? Justify.
OR
Draw the circuit diagram of a full wave rectifier and briefly explain its working principle.
Q 7 What does the term LOS communication mean? Name the types of waves that are used for this communication. Which of the two-height of transmitting antenna and height of receiving antenna can effect the range over which this mode of communication remains effective?
Q.8 Derive the expression for the self inductance of a solenoid.
Q.9 A series LCR circuit with R=20Ω, L=1.5H and C=35μf is connected to a variable frequency 200 volt ac supply. When the frequency of supply equals to the naturals frequency of the circuit, what is the average power transferred to the circuit in one complete cycle?
Q.20 In the circuit figure E, F, G and H are cells of emf 2, 1, 3 and 1 volt and their internal resistances are 2, 1, 3 and 1Ω respectively. Calculate
(i) The potential difference between B and D
(ii) The potential difference across the terminals and each of the cells G and H.