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CBSE Class 12 Pre Board 2020 : Physics - Prelim 2 (Delhi Public School (DPS), Jammu)

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DELHI PUBLIC SCHOOL JAMMU Session (2019-20) Pre-Board II Assignment for Class 12th Subject- Physics Q01 A plane mirror makes an angle of 30o with horizontal. If a vertical ray strikes the mirror, find the angle between mirror and reflected ray (a) 30o (b) 45o (c) 60o (d) 90o Q02 An object of length 2.5 cm is placed at a distance of 1.5 f from a concave mirror where f is the magnitude of the focal length of the mirror. The length of the object is perpendicular to the principle axis. The length of the image is (a) 5 cm, erect (b) 10 cm, erect (c) 15 cm, erect (d) 5 cm, inverted Q03 32. An object of length 6cm is placed on the principal axis of a concave mirror of focal length f at a distance of 4 f. The length of the image will be (a) 2 cm (b) 12 cm (c) 4 cm (d) 1.2 cm Q04 The masses of neutron and proton are 1.0087 amu and 1.0073 amu respectively. If the neutrons and protons combine to form a helium nucleus (alpha particles) of mass 4.0015 amu. The binding energy of the helium nucleus will be [1 amu= 931 MeV] (a) 28.4 MeV (b) 20.8 MeV (c) 27.3 MeV (d) 14.2 MeV Q05 The counting rate observed from a radioactive source at t = 0 second was 1600 counts per second and at t = 8 seconds it was 100 counts per second. The counting rate observed as counts per second at t = 6 seconds will be (a) 400 (b) 300 (c) 200 (d) 150 Q06 A potential difference of V is applied at the ends of a copper wire of length l and diameter d. On doubling only d, drift velocity (a) Becomes two times (b) Becomes half (c) Does not change (d) Becomes one fourth Q07 An aluminium rod of length 3.14 m is of square cross-section 3.14 3.14 mm2. What should be the radius of 1 m long another rod of same material to have equal resistance (a) 2 mm (b) 4 mm (c) 1 mm (d) 6 mm Q08 The de-Broglie wavelength of a neutron at 27oC is . What will be its wavelength at 927oC (a) /2 (b) / 3 (c) / 4 (d) / 9 15 Q09 Light of frequency 8X10 is incident on a substance of photoelectric work function 6.125 eV. The maximum kinetic energy of the emitted photoelectrons is (a) 17 eV (b) 22 eV (c) 27 eV (d) 37 eV Q10 A wire of fixed length is turned to form a coil of one turn. It is again turned to form a coil of three turns. If in both cases same amount of current is passed, then the ratio of the intensities of magnetic field produced at the centre of a coil will be (a) 9 times of first case (b) times of first case (c) 3 times of first case (d) times of first case Q11 Two solenoids having lengths L and 2L and the number of loops N and 4N, both have the same current, then the ratio of the magnetic field will be (a) 1:2 (b) 2:1 (c) 1:4 (d) 4:1 Q12 While a collector to emitter voltage is constant in a transistor, the collector current changes by 8.2 mA when the emitter current changes by 8.3 mA. The value of forward current ratio hfe is (a) 82 (b) 83 (c) 8.2 (d) 8.3

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