A school’s physics laboratory uses the following electrical equipment

PHYSICS · Multi-part · CBSE · Physics · Current Electricity · Current Electricity

Problem

A school’s physics laboratory uses the following electrical equipment. •

40

fluorescent lamps of

40\,\text{W}

each, switched on for

6\,\text{h}

daily. •

10

desktop computers of

120\,\text{W}

each, operated for

5\,\text{h}

daily. •

20

ceiling fans of

60\,\text{W}

each, running for

7\,\text{h}

daily. The cost of electrical energy is Rs

5.50

per kWh. (i) Show that

1\,\text{kWh}

of electrical energy is equal to

3.6\times10^{6}\,\text{J}

. (ii) Calculate the total electrical energy consumed by the laboratory in one day, expressed in kWh. (iii) Determine the electricity cost for a

30

-day month. (iv) The school plans to replace all the fluorescent lamps with

18\,\text{W}

LED lamps of the same number and usage time. Calculate the percentage reduction in the monthly electricity cost after replacement.