How will the current strength in the lamp change if the voltage is reduced by 3 times?

Given:

U2 = U1 / 3 – the voltage of the electrical network was reduced by 3 times.

It is required to determine I2 / I1 – how will the current flowing through the electric lamp change.

Let R be the resistance of an electric lamp.

Then, the current strength in the first case will be equal to:

I1 = U1 / R.

The current strength in the second case will be equal to:

I2 = U2 / R = (U1 / 3) / R = U1 / (3 * R).

From here we find that:

I2 / I1 = (U1 / (3 * R)) / (U1 / R) = 1/3, that is, it will decrease by 3 times.

Answer: when the voltage is reduced by 3 times, the current in the lamp will also decrease by 3 times.