Subject

Physics

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

11.

A circular coil of cross-sectional area 200 cm2 and 20 turns is rotated about the vertical diameter with angular speed of 50 rad s−1 in a uniform magnetic field of magnitude 3.0 × 10−2T. Calculate the maximum value of the current in the coil.

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12.

A wire whose cross-sectional area is increasing linearly from its one end to the other, is connected across a battery of V volts.
Which of the following quantities remain constant in the wire?
(a) drift speed
(b) current density
(c) electric current
(d) electric field

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13.

Name the junction diode whose I-V characteristics are drawn below

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14.

Define the distance of closest approach. A α-particle of kinetic energy 'K' is bombarded on a thin gold foil. The distance of the closest approach is 'r'. What will be the distance of closest approach for a α-particle of double the kinetic energy?   

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15.

Write two important limitations of Rutherford nuclear model of the atom.

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16. Find out the wavelength of the electron orbiting in the ground state of the hydrogen atom.
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17. Define the magnifying power of a compound microscope when the final image is formed at infinity. Why must both the objective and the eyepiece of a compound microscope has short focal lengths? Explain.
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18.

Which basic mode of communication is used in satellite communication? What type of wave propagation is used in this mode? Write, giving a reason, the frequency range used in this mode of propagation.

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19. Write the two processes that take place in the formation of a p-n junction. Explain with the help of a diagram, the formation of the depletion region and barrier potential in a p-n junction.  
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20.

(i) Obtain the expression for the cyclotron frequency.
(ii) A deuteron and a proton are accelerated by the cyclotron. Can both be accelerated with the same oscillator frequency? Give reason to justify your answer.


When a charged particle (q) moves inside a magnetic field B with velocity v, it experiences a force F = q(v xB) when v is perpendicular to B, the force F on the charged acts as the centripetal force and makes it move along a circular path.
Let m be the mass of particle and r is radius  of circular path

straight q space left parenthesis straight v with rightwards arrow on top space straight x straight B with rightwards arrow on top right parenthesis space equals space mv squared over straight r
qvB space equals space mv squared over straight r
rightwards double arrow space straight r space equals space mv over Bq

Time period of the circular motion of a charged particle is given by

straight T space equals space fraction numerator 2 πr over denominator straight v end fraction
space equals fraction numerator 2 πmv over denominator straight v space Bq end fraction
rightwards double arrow space straight T space equals space fraction numerator 2 πm over denominator Bq end fraction
Angular space frequency space comma
straight omega space equals space fraction numerator 2 straight pi over denominator straight T end fraction
therefore space straight omega space equals space Bq over straight m
ii) No, The mass of the two particles, i.e deuteron and proton, is different.Since (cyclotron) frequency depends inversely on the mass, they cannot be accelerated by the same oscillator frequency.

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