How does a switchmode voltage regulator work?

A switchmode voltage regulator operates by rapidly turning a series control element fully on and fully off, creating a train of voltage pulses. Instead of absorbing excess power as heat like a linear regulator, it efficiently chops the input DC voltage into high-frequency pulses. The regulator maintains a constant output voltage by varying the duty cycle of these pulses—that is, the ratio of the "on" time to the "off" time. A longer "on" time results in a higher average voltage, while a shorter "on" time reduces it. These pulses are then fed into an LC (inductor-capacitor) filter, which smooths the rapidly switching pulses back into a steady DC output. The option regarding "varying the conductivity of a pass element" perfectly describes a linear regulator, which is the exact opposite of switchmode operation.