Question

Seeta says that a compact fluorescent lamp uses less energy compared to an incandescent bulb. But Geeta, her friend, does not agree with this. Seeta proves it by calculating the money that can be saved per month by using a compact fluorescent lamp of $15W$ in place of an incandescent lamp of $100W$ if they are used $8hours$ per day for $30days$. How did she prove it? (The cost of one unit of electrical energy is $2rupees$)

Answer 1

Step 1: Given data:

Power of fluorescent lamp $=15W$

Power of incandescent lamp $=100W$

time$=30days$

daily usage $=8hours$

charge of every single unit$=Rs.2$

The formula used is given as,

$Energyconsumed(inkWh)=\frac{power\times time}{1000}$

Step 2: Finding the money saved:

1. : The energy consumed in operating a fluorescent lamp,

$$\begin{gathered} Energy=15\times 8\times 60\times 60\times 30J \\ =\frac{15\times 8\times 36\times 3}{36\times {10}^5}kWh \\ =3.6kWh \end{gathered}$$

The cost will be

$$\begin{gathered} \cos t=3.6\times 2 \\ =7.2rupees \end{gathered}$$

2. Energy consumed in the incandescent bulb is,

$$\begin{gathered} Energy=100\times 8\times 60\times 60\times 30J \\ =\frac{8\times 36\times 3\times {10}^3}{36\times {10}^5}kWh \\ =24kWh \end{gathered}$$

The cost will be

$$\begin{gathered} \cos t=2\times 24 \\ =48rupees \end{gathered}$$

saved money$=48-7.2rupees$

$=40.8rupees$