Sebuah lampu pijar 40 W/220 V setiap hari digunakan selama 10 jam. Jika lampu tersebut diganti dengan sebuah lampu hemat energi dengan efisiensi 60 % dari lampu pijar, maka energi yang dapat dihemat sebesar

<p>P = 40 watt</p><p>V = 220 volt</p><p>t = 10 jam = 10 x 3600 sekon = 36.000 sekon</p><p>&nbsp;</p><p>W = P x t</p><p>&nbsp; &nbsp; &nbsp;= 40 x 36.000</p><p>&nbsp; &nbsp; &nbsp;= 1.440.000 Joule</p><p>&nbsp; &nbsp; &nbsp;= 1.440 kJ</p><p>&nbsp;</p><p>Energi yang dihemat = 60% x 1.440.000</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; = 60/100 x 1.440.000</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; = 864.000 Joule</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; = 864 kJ</p><p>&nbsp;&nbsp;</p><p>&nbsp;</p>