Question

An electric lamp is marked 100w, 220v. lt is used for 5hours daily. calculate (I) its resistance while glowing (II) energy consumed in kWh per day

Answer 1

power = voltage ÷ resistance

Answer 2

Given :
power =p=100w
voltage=220V
time=2hrs
Resistance=R=?
Formula to be used :
P=V*I
BUT I=V/R
∴P=V²/R
⇒R=V²/P
      =220x220/100
       =484ohms
To calculate Energy consumed :
Formula : E=Pxt
                  =100x5
                  =500Wh
                  =500/1000 kWh
                  0.5 kWh
    ∴ Resistance while glowing is 484 ohms and  energy consumed in kWh per day ps 0.5