12. The circuit diagram shown in Fig. 8.34 includes a 6 V battery, an ammeter A, a fixed resistor R

12. The circuit diagram shown in Fig. 8.34 includes a 6 V battery, an ammeter A, a fixed resistor R_{I} of 2 2 and a resistance wire R_{2} connected between the terminals A and B. The resistance of the battery and ammeter may be neglected. Calculate the ammeter readings when the wire R_{2} is of

(a) 0-20 m length and of resistance 4 Ω.

(b) 0-40 m length and of the same thickness and material as in case (a).

(c) 0.20 m length and of area of cross section double than that in case (a).