If a resistance coil is made by joining in parallel two resistances each of 20$\Omega$. An emf of 2V is applied across this coil for 100 seconds. The heat produced in the coil is

(1) 20 J

(2) 10 J

(3) 40 J

(4) 80 J

$\mathrm{In} \mathrm{the} \mathrm{circuit} \mathrm{shown} \mathrm{in} \mathrm{figure} \mathrm{if} \mathrm{power} \mathrm{dissipated} \mathrm{in} 9\mathrm{\Omega } \mathrm{resistor} \mathrm{is} 144\mathrm{W}, \mathrm{then} \mathrm{potential} \mathrm{difference} \mathrm{across} 3.6\mathrm{\Omega } \mathrm{resistor} \mathrm{will} \mathrm{be}$

1.  36V

2.  18V

3.  9V

4.  Zero

For driving a current of 2 A for 6 minutes in a circuit, 1000 J of work is to be done. The e.m.f. of the source in the circuit is 

(1) 1.38 V

(2) 1.68 V

(3) 2.04 V

(4) 3.10 V

Consider four circuits shown in the figure below. In which circuit power dissipated is greatest (Neglect the internal resistance of the power supply)

(1)

(2)

(3)

(4)

A battery is charged at a potential of 15 V for 8 hours when the current flowing is 10 A. The battery on discharge supplies a current of 5 A for 15 hours. The mean terminal voltage during discharge is 14 V. The "Watt-hour" efficiency of the battery is :

(1) 82.5%

(2) 80 %

(3) 90%

(4) 87.5%