Relay basics: A relay is an electromagnetically controlled mechanical device whose contacts open or close when a magnetizing current energizes the coil. True or false?

Introduction / Context:
Relays provide galvanic isolation and allow low-power control circuits to switch higher voltages and currents. Understanding their operating principle helps in designing protection, automation, and control systems.

Given Data / Assumptions:

• An electromagnetic relay contains a coil, armature, spring, and one or more contact sets (NO/NC).
• Applying coil current creates a magnetic field that attracts the armature.
• Contact motion is mechanical and may include bounce and release hysteresis.

Concept / Approach:

When coil current flows, the magnetic field produces an attractive force on the armature, overcoming the return spring and closing or opening contacts depending on configuration. Removing current collapses the field, allowing the spring to restore the original contact state. This electromechanical transduction defines a relay.

Step-by-Step Solution:

Verification / Alternative check:

Measure continuity across NO/NC contacts while toggling coil voltage. The mechanical contact state should follow coil energization, confirming electromagnetic control of contact operation.

Why Other Options Are Wrong:

• “False” would deny the fundamental electromagnetic mechanism that defines classical relays; solid-state relays use different physics but are a distinct category.

Common Pitfalls:

Ignoring coil voltage ratings and contact current limits; miswiring NO vs. NC; underestimating contact bounce and required snubbers for inductive loads.

Final Answer:

True