Answer to Question #115214 in Optics for Vidurjah Perananthan

Question

Many years ago, in the public grid, there was an alternating voltage of the effective value 127
1.On an old lamp from that time is 127 V; 40 W. Today is the mains voltage
effective value 230
2. What would happen if this lamp were used today?

Answer 1

As per the question,

The initial effective value of the voltage =127V and 40W

The resistance of the lamp $(R)=\dfrac{V^2}{P}=\dfrac{127^2}{40}$

When the effective voltage is changed to 230V, then the power of the lamp

$P=\dfrac{V^2}{R}$

Now substituting the values,

$P=\dfrac{230^2\times 40}{127^2}=131.2W$