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

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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%