Long Answer TypeDefine magnifying power of a telescope. Write its expression.
A small telescope has an objective lens of focal length 150 cm and an eye piece of focal length 5 cm. If this telescope is used to view a 100 m high tower 3 km away, find the height of the final image when it is formed 25 cm away from the eye piece.
Draw a simple circuit of a CE transistor amplifier. Explain its working. Show that the voltage gain AV, of the amplifier is given by 
, where 
is the current gain, RL is the load resistance and ri is the input resistance of the transistor. What is the significance of the negative sign in the expression for the voltage gain?
Draw the circuit diagram of a full wave rectifier using p-n junction diode. Explain its working and show the output, input waveforms.
(b) Show the output waveforms (Y) for the following inputs A and B of
(i) OR gate
a)
Working: The AC input voltage across secondary s1 and s2 changes polarity after each half cycle. Suppose during the first half cycle of input AC signal, the terminal s1 is positive relative to centre tap O and s2 is negative relative to O. Then diode D1 is forward biased and diode D2 is reverse biased. Therefore, diode D1 conducts while diode D2 does not. The direction of current (i1) due to diode D1 in load resistance RL is directed from A to B. In next half cycle, the terminal s1 is negative and s2 is positive relative to centre tap O. The diode D1 is reverse biased and diode D2 is forward biased. Therefore, diode D2 conducts while D1does not. The direction of current (i2 ) due to diode D2 in load resistance RL is still from A to B. Thus the current in load resistance RL is in the same direction for both half cycles of input AC voltage. Thus for input AC signal the output current is a continuous series of unidirectional pulses.
In a full wave rectifier, if input frequency is f hertz, then output frequency will be 2f hertz because for each cycle of input, two positive half cycles of output are obtained.
b) Output waveforms for the following inputs A and B of OR gate and NAND gate.
Switch
