Calculate the resistance of the filament of a lamp rates 240 V, 40 W

  • A 240Ω
  • B 360Ω
  • C 720Ω
  • D 1440Ω
  • E 2880Ω
waec 1990physics

The correct answer is D. 1440Ω

The resistance of the filament of a lamp can be calculated using Ohm’s law and the power formula.

According to Ohm’s law, the voltage (V) across a resistor is equal to the current (I) through it times its resistance or V = IR.

The power (P) consumed by a resistor is given by the formula P = IV.

Substituting Ohm’s law into the power formula gives P = I^2R = V^2/R.

Solving for R gives R = V^2/P.

Given that V = 240 V and P = 40 W, we can substitute these values into the formula:

R = (240 V)^2 / 40 W = 1440 Ω

So, the resistance of the filament of the lamp is 1440 Ω (Option D).

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