Which device in electrical systems uses a small current to control a larger current?

Which device in electrical systems uses a small current to control a larger current?

• A. In automotive circuits, a relay converts high voltage to low voltage
• B. A relay uses a small current to control a larger current
• C. A relay stores electrical energy
• D. A relay measures voltage drop

Answer: (B)

Relays work by using a small control current to energize a coil, which creates a magnetic field that pulls the switch contacts to open or close. This allows a high-current circuit to be controlled by a much smaller current in a separate circuit, keeping the two circuits isolated. In automotive wiring, that means a tiny signal from a switch or computer can control a powerful device like a motor, lamp, or fuel pump without running the high current through the control line. The other ideas don’t fit the same role: storing energy is done by components like capacitors or batteries, not by a relay; measuring voltage drop is the job of a meter or sensor, not a switching device; and while transformers handle changing voltage levels, a relay doesn’t inherently convert voltage—it simply connects or disconnects a high-current path as controlled by a low-current coil.

Relays work by using a small control current to energize a coil, which creates a magnetic field that pulls the switch contacts to open or close. This allows a high-current circuit to be controlled by a much smaller current in a separate circuit, keeping the two circuits isolated. In automotive wiring, that means a tiny signal from a switch or computer can control a powerful device like a motor, lamp, or fuel pump without running the high current through the control line.

The other ideas don’t fit the same role: storing energy is done by components like capacitors or batteries, not by a relay; measuring voltage drop is the job of a meter or sensor, not a switching device; and while transformers handle changing voltage levels, a relay doesn’t inherently convert voltage—it simply connects or disconnects a high-current path as controlled by a low-current coil.