c What values of the boy reflect from the conversation SECTION E 24 State the

# C what values of the boy reflect from the

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(c) What values of the boy reflect from the conversation? 24. State the working principle of a potentiometer. Draw a circuit diagram (a) to compare the emfs of two primary cells. (b) to find the internal resistance of a cell. Derivethe formula used.How can the sensitivity of a potentiometer be increased? 25. Draw the circuit diagram of an n - p - n transistor in common emitter configuration to study its (a) input and (b) output characteristics. Draw approximate shapes of these characteristics. Using these characteristics, explain how you would find the input and output resistance of the transistor. 18. A spherical capacitor consists of two concentric spherical conductors held in position by a suitable insulating support. Show that the capacitance of a spherical capacitor is given by C = 4 0 1 2 1 2 πe r r r r . Where r 1 and r 2 are the radii of outer and inner spheres, respectively. 19. The total energy of an electron in the first excited state of the hydrogen atom is about – 3.4 eV. (a) What is the kinetic energy of the electron inthis state? (b) What is the potential energy of the electron in this state? (c) Which of the answers above would change if the choice of the zero of potential energy is changed? 20.What is photoelectric effect? Write Einstein'sphotoelectric equation. Explain how it enables us tounderstand the (a) linear dependence of the maximum kinetic energy of the emitted electrons, on the frequency of the incident radiation. (b) existence of a threshold frequency for a given photoemitter. (c) independence of the maximum energy of emitted photoelectrons from the intensity of incident light. 21. Answer the following questions: (a) Why does a paramagnetic sample displaygreater magnetisation for the same magnetising field when cooled? (b) Why is diamagnetism, in contrast, almost independent of temperature? (c) Is the permeability of a ferromagnetic material independent of the magnetic field? If not, is it more for lower or higher fields? 22. (a) In what way is diffraction from each slit related to the interference pattern in a double slit experiment?
OR (a) State briefly the processes involved in the formation of p - n junction explaining clearly how the depletion region is formed.

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