Explain, with the help of a circuit diagram, the working of a photo diaode. Write briefly how it is used to detect the optical signals.

Explain with the help of a circuit diagram, the working of a p-n junction diode as a half wave rectifier.

Write the principle of working of a potentiometer. Describe briefly, with the help of a circuit diagram, how a potentiometer is used to determine the internal resistance of a given cell.

State the working principle of potentiometer. With the help of the circuit diagram, explain how a potentiometer is used to compare the emf's of two primay cells. Obtain the required expression used for comparing the emfs. Write two possible causes for one sided deflection in a potentiometer experiment.

State the underlying principle of a cyclotron. Write briefly how this machine is used to accelerate charged particles to high energies.

(i) Draw a circuit diagram to study the input and output characteristics of an n-p-n transistor in its common emitter configuration. Draw the typical input and output characteristics. (ii) Explain, with the hepl of a circuit diagram, the working of n-p-n transistor as a common emitter amplifier.

Describe briefly with the help of a circuit diagram, how the flow of current carriers in a p-n-p transistor is regulated with emitter-base junction forward biased and base-collector junction reverse biased.

(a) Explain with the help of suitable diagram , the two processes which occur during the formations of a p -n junction diode . Hence , define the terms : (i) depletion region and (ii) potential barrier : (b) Draw a circuit diagram of a p - n junction diode under forward bias and explain its working .

(a) For a ray of light travelling from a denser medium of refractive index n_(1) to a rarer medium of refractive index n_(2) , prove that (n_(2))/(n_(1)) = sin i_(c) , where i_(c) is the critical angle of incidence for the media. (b) Explain with the help of a diagram, how the above principle is used for transmission of video signals using optical fibers.

(a) Derive the relationship between the peak and the rms value of current in an a.c. circuit. (b) Describe briefly, with the help of a labelled diagram, working of a step-up transformer. A step-up transformer converts a low voltage into high voltage. Does it not violate the principal of conservation of energy? Explain.

Answer the following: (a) With the help of a diagram , explain the principle and working of a moving coil galvanometer . (b) What is the importance of a radial magnetic field and how is it produced ? (c) Why is it while using a moving coil galvometer as a voltmeter a high resistance in series is required whereas in an ammeter a shunt is used ?