Question

A electric bulb is rated 240v,40w.calculate 1-the electric current through it .2-the resistance of filament.3-energy consumed by it in kw when it is used for 5 hours

Answer 1

power (P) = voltage (V) x current (I)
=> I = P/V (given P=40W, V = 240V)
=> I = 40/240 = 1/6 Amperes

now, votlage(V) = ccurrent(I) x resistance (R)
=>                R= V/I
                       = 240x6 = 1440ohms

energy consumed = power x time 
                               =40 x 5 = 200W-h = 0.2kwh

Answer 2

Voltage Rating = V = 240 Volts        power = 40 Watts 
Power P = V * I
current I = P / V = 40/240 = 0.167 Amp

Resistance R = V / I   or  V² / P = 240² / 40 = 1440 Ω

Energy consumed in 5 hours
  = P * t =  40 * 5 * 3600 = 720 kJ

Energy consumed in kWh kilo watt hours: = 40 W * 5 hrs = 200 Wh
          = 0.200 kWh