Rajasthan Police Constable Model Paper 8

CONCEPT:

• Power: The rate of work done by an electric current is called power. It is denoted by P. The SI unit of power is the watt (W).

Power dissipation is given by:
Power (P) = V I = ${\mathit{V}}^2$ /R = I ${}^2$ R
Where V is the potential difference across resistance, I is current flowing and R is resistance.
Heat dissipation/work done/Electrical energy is given by:
Heat dissipated (H) = Power (P) × Time (t)
CALCULATION:
Given that:
Power (P) = 400 W
Per day working time = 8 hrs
Total days = 30 days
Cost per unit = 2.5 per kWh
Total time (t) = 8 × 30 = 240 hrs
2 2The total energy consumed by the refrigerator in 30 days would be:
Energy (H) = P × t = 400 × 240 hrs = 96000 Wh = 96 kWh
The cost of energy to operate the refrigerator for 30 days = total energy × cost per unit = 96 kW h × Rs 2.50 per kW h = Rs 240.00.
Hence option 4 is correct.