question_answer

(a) Name an instrument that measures electric current in a circuit. Define the unit of electric current. (b) What do the following symbols mean in circuit diagrams? (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. (c) Draw a diagram of the electric circuit 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 l values 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? Or In a household electric circuit, different applianes are connected to parallel to one another. Give two reasons. An electrician puts a fuse of rating 5 A in that part of domestic electrical circuit in which an electrical heater of rating 1.5 kW, 220 V is operating. What is likely to happen in this case and why? What changes, if any, needs to be made?  

Answer:

(a) Ammeter is used to measure current. Its unit of current is ampere A. One ampere is defined as the current which will flow in a resistor of  when 1 V potential difference is applied across it ends.            (1) (b) (i) Rheostat                 (ii) Closed key                                             (1) (c) (i) An electric circuit given relation is shown below (ii) From the graph, when potential difference is 1.6 V and current is 0.6 A.   Therefore, value of  ratio for all potential difference 0.8 V, 1.2 V and 1.6 V will be equal to 2.67 .      (1) We conclude that at the given temperature, the resistance of wire is constant and is equal to 2.67 .    (1) Or In a household electric circuit, different appliances are connected in parallel to one another because (i) Each appliance may be independently used. (ii) Each appliance may get the required potential.                              (1 x 2) Given, P = 1.5 kW = 1500 W, V = 220 V Current drawn                                                     (1) The fuse wire will melt and disconnect the electrical heater from the mains since it can bear only 5A. But to run the heater, instead of 5A fuse, one should use a fuse with a slightly higher capacity to handle a current more than 6.82 A, thus a 10 A fuse is required.                                                                                                                   (2)