Question

fifty lamps each of resistance 100 ohm are connected in parallel across a 220V main. find the (a) power consumed in watts and (b) the cost of operating the lamps for 20 hours at 10 paise per K Wh​

Answer 1

Answer:-

• Resistance of each lamp=R=100ohm

Resistance of 50 lamps:-

$\\ \sf{:}\longrightarrow 50\times 100$

$\\ \sf{:}\longrightarrow 5000\Omega$

• Voltage=V=220V

We know that

$\boxed{\sf Power=\dfrac{V^2}{R}}$

$\\ \sf{:}\longrightarrow Power=\dfrac{(220)^2}{5000}$

$\\ \sf{:}\longrightarrow Power=\dfrac{48400}{5000}$

$\\ \sf{:}\longrightarrow Power=9.6watts$

Finding Work done

$\\ \sf{:}\longrightarrow W=Pt$

$\\ \sf{:}\longrightarrow Work\:done=9.6\times 20$

$\\ \sf{:}\longrightarrow Work\:done=192Wh$

• Bill per kwh=10paise
• Bill per wh=10/1000=0.1paise

$\\ \sf{:}\longrightarrow Bill\:per\:192wh=192\times 0.1$

$\\ \sf{:}\longrightarrow Bill\:per\:192wh=19.2paise$