Page 36 - Physics - XII
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VIVA VOCE



               Q1.  What type of galvanometer is used in laboratories?
              Ans.  Weston type galvanometer is used in the laboratory.

               Q2.  What is the principle of the galvanometer?
              Ans.  The  defl ection  produced  in  the  galvanometer  is  directly  proportional  to  the  current  passing
                     through its coil.
               Q3.  How do you determine the resistance of the galvanometer?
              Ans.  By half-defl ection method.

               Q4.  Why this method is called half-defl ection method?
              Ans.  It is so called because the defl ection is made half by using a shunt resistance.

               Q5.  Why should an ammeter have a very small resistance?
              Ans.  So that when an ammeter is connected in series in a circuit, it should not reduce much of the original
                     current which is to be measured.

               Q6.  Give the formula for the calculation of the shunt resistance, so that a galvanometer can be
                     converted into an ammeter by connecting it in parallel to the galvanometer.

              Ans.   S    I g    G  , where G is the galvanometer resistance, I is the range of the ammeter, and Ig is the
                          I    I g
                     amount of current which gives the full scale defl ection in the galvanometer.
               Q7.  What is a galvanometer?
              Ans.  It is a device which is used to detect the feeble electric currents.

               Q8.  What is the resistance of a galvanometer?
              Ans.  It is the resistance off ered by the coil of the galvanometer to fl ow the current through it.
               Q9.  What is meant by range of an ammeter?
              Ans.  It is the maximum value of the current which the ammeter can measure.

               Q10.  What is a voltmeter?
              Ans.  It is an instrument which is used to measure the potential diff erence between two points in an
                     electric circuit.

               Q11.  How is a galvanometer converted into a voltmeter?
              Ans.  A galvanometer is converted into a voltmeter by connecting a high resistance in series with the
                     galvanometer coil.

               Q12.  Why is it necessary for a voltmeter to have a high resistance?
              Ans.  A voltmeter is connected in parallel across two points in a circuit. If it has a low resistance, it will
                     decrease the value of actual potential diff erence to be measured between these two points.
               Q13.  How do you compute the resistance which is to be connected in series with the galvanometer

                     to convert it into a voltmeter of desired range?
              Ans.  It is computed by the following relation
                          V
                     R         G , where the symbols have their usual meanings.
                          I g

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