question_answer

                            [CBSE Delhi 2008]  (a) Name an instrument that measures electric current in a circuit. Define the unit of electric current. (b) What do the following symbols represent in a circuit diagram? (i)       (ii) (c) An electric circuit consisting of a 0.5 m long nichrome wire XY, an ammeter, a voltmeter, four cells of 1.5 V each and a plug key was set up. (i) Draw the electric circuit diagram to study the relation between the potential difference maintained between the points 'X' and 'Y' and the electric current flowing through XY. (ii) Following graph was plotted between V and I values using above circuit: What would be the values of? ratios when the potential difference is 0.8 V, 1.2 V and 1.6 V, respectively? What conclusion do you draw from these values?   [CBSE Delhi 2008]

Answer:

                  (a) An instrument that measures electric current in a circuit is called "ammeter". The unit of electric current is ampere (A). 1 ampere is constituted by the flow of 1 coulomb of charge through any point in an electric circuit in 1 second. (b) (i)      (ii) Variable resistance          Plug key or switch or rheostat                                   (closes) (c) (i) (ii) Following graph was plotted between V and I Values. At potential difference 0.8V,                 At potential difference 1.2 V,                                                                 Conclusion: If  be the current through XY resistor and V be the potential difference across it, then the ratio constant.         and Ohm's law is oeyed.