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

If I be the current limit of a fuse wire of length l and radius r, then select the appropriate relation

1. $I<mspace\; width="1em"></mspace>\alpha <mspace\; width="1em"></mspace>l$

2. $I<mspace\; width="1em"></mspace>\alpha <mspace\; width="1em"></mspace>r^2$

3. $I<mspace\; width="1em"></mspace>\alpha <mspace\; width="1em"></mspace>l^0$

4. $I<mspace\; width="1em"></mspace>\alpha <mspace\; width="1em"></mspace>r^0$

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%

The maximum power drawn out of the cell from a source is given by (where r is internal resistance)  

1. $E^2/2r$

2. $E^2/4r$

3. $E^2/r$

4. $E^2/3r$

In the following circuit, bulb rated as 1.5 V, 0.45 W. If bulbs glows with full intensity then what will be the equivalent resistance between X and Y

1. 0.45 Ω

2. 1 Ω

3. 3 Ω

4. 5 Ω

Two cities are 150 km apart. Electric power is sent from one city to another city through copper wires. The fall of potential per km is 8V and the  average resistance per km is 0.5 Ω. The power loss in the wire is

1. 19.2W
 

2. 19.2kW
 

3. 19.2J
 

4. 12.2kW 

If voltage across a bulb rated 220 V-100 W drops by 2.5% of its rated value, the percentage of the rated value by which the power would decrease is

1. 20%                                             

2. 2.5%

3. 5%                                               

4. 10%