Q20 of 31 Page 1

State the principle of working of a galvanometer.

A galvanometer of resistance G is converted into a voltmeter to measure up to V volts by connecting a resistance in series with the coil. If a resistance is connected in series with it, then it can measure up to V/2 volts. Find the resistance, in terms of and, required to be connected to convert it into a voltmeter that can read up to 2 V. Also find the resistance G of the galvanometer in terms of and.


When a current-carrying coil is placed in a magnetic field, it experiences a torque. From the measurement of the deflection of the coil, the strength of the current can be computed. A high resistance is connected in series with the galvanometer to convert it into voltmeter. The value of the resistance is given by:



Here, V= potential difference across the terminal of the voltmeter


= Current through galvanometer


G= Resistance of the galvanometer


When the resistance is connected in series with the galvanometer.


V=I (G+)


When the resistance is connected in series with the galvanometer.


=I (G+)



G=


Let be the resistance required for conversion into voltmeter of range 2V



Also V=




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18

A cell of emf ‘E’ and internal resistance ‘r’ is connected across a variable load resistor R. Draw the plots of the terminal voltage V versus (i) R and (ii) the current I. It is found that when R = 4 W, the current is 1 A and when R is increased to 9 W, the current reduces to 0.5 A. Find the values of the emf E and internal resistance r.

 19

Two capacitors of unknown capacitances and are connected first in series and then in parallel across a battery of 100 V. If the energy stored in the two combinations is 0.045 J and 0.25 J respectively, determine the value of and. Also calculate the charge on each capacitor in parallel combination.

 21

With what considerations in view, a photodiode is fabricated? State it’s working with the help of a suitable diagram.

Even though the current in the forward bias is known to be more than in the reverse bias, yet the photodiode works in reverse bias. What is the reason?


 22

Draw a circuit diagram of a transistor amplifier in CE configuration.

Define the terms: (i) Input resistance and (ii) Current amplification factor. How are these determined using typical input and output characteristics?