Question

Why does halving the voltage in a power supply not always halve the current?

Answer 1

Current is not fixed, its dependent on the resistance which is fixed in this question. So a simple reason is that is the voltage is halved the current is also halved (By ohm’s law).

The power is the product of Voltage times current.

If both are halved then the power after that is only 1/4 of the power.

If the voltage was doubled then the power would be quadrupled.

This “squared” relation between power, voltage and resistance is easily derived.

Given Ohm’s law V=I * R which also means I = V/R

and P = I * V

the P = V * V / R = V^2/R

Answer 2

Current is not fixed, its dependent on the resistance which is fixed in this question. So a simple reason is that is the voltage is halved the current is also halved (By Ohm's law).

The power is the product of Voltage times current.

If both are halved then the power after that is only 1/4 of the power.

If the voltage was doubled then the power would be quadrupled.

This “squared” relation between power, voltage, and resistance is easily derived.

Given Ohm’s law V=I * R which also means I = V/R

and P = I * V

the P = V * V / R = V^2/R