Question

A certain household has consumed 250 units of energy during a month. This energy in joules is .

• A. $8\times {10}^{8}J$
• B. $8\times {10}^{9}J$
• C. $9\times {10}^{9}J$
• D. $9\times {10}^{8}J$

Answer 1

The correct option is D $9\times {10}^{8}J$

Units of energy consumed = 250 units
This ‘unit’ term means a commercial unit of power which is actually kilowatt-hour (kWh).
Therefore,
Energy $=250kWh=250\times 1000Wh(k=kilo=1000)$
$\Rightarrow Energy=250\times 1000\times 60\times 60Ws(h=hour=60\times 60s)$
$\Rightarrow Energy=9\times {10}^{8}J(Ws=J)$