The device in which one circuit controls another, especially if the current in the second circuit is large or dangerous is known as

1. Analyze the question

The question asks for the name of a specific electrical device that acts as a switch. Its primary function is to allow a low-power or safe circuit to control a separate circuit that might carry a high voltage or a large, dangerous current.

2. Explain the concept

This device is based on the principle of electromagnetism.

• How it works: When a small current flows through the coil of the device, it creates a magnetic field. This magnetic field attracts a metal armature (a switch), which then closes or opens the contacts of the second, high-power circuit.
• Why use it? It provides electrical isolation. By using a relay, the person operating the switch (e.g., a light switch or a remote control) is physically separated from the high-voltage circuit, preventing electric shocks and allowing for automation.

3. Show the solution

• Option A (Electromagnetic devices): This is a broad category. While a relay is an electromagnetic device, the term is too general; it could refer to motors, generators, or speakers.
• Option B (Magnetic relay device): This is the specific name for the switch described. It uses an electromagnet to operate a mechanical switch, making it the perfect answer for controlling high-current circuits safely.
• Option C (None at all): Incorrect, as the device described exists.
• Option D (Sextant): This is a navigational instrument used to measure the angle between two visible objects; it has nothing to do with electrical circuits.

4. Identify the answer

The correct device is a Magnetic relay. It is specifically designed to isolate control circuits from high-power load circuits.

5. Exam Tip

When you see the word "control" and "dangerous/large current" in a Physics question, immediately look for the word "Relay." Think of a relay as a "middleman" that does the dangerous work so you don't have to touch the high-voltage wires directly!