Question

Which of the following devices does NOT use magnetic effect of electric current?

• A. Electric bell
• B. Electric motor
• C. Electric generator
• D. Electric heater

Hint:

Always categorize electrical appliances by their primary effect:
- Thermal effect: Heaters, irons, toasters, fuses.
- Magnetic effect: Bells, motors, generators, relays.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the device from the given options that does not operate on the principles of electromagnetism or the magnetic effect of electric current.

Step 2: Key Formula or Approach:
Analyze the working principle of each device:

• Electric Bell: Uses an electromagnet to pull a clapper to strike a gong.

• Electric Motor: Uses the force acting on a current-carrying coil placed in a magnetic field.

• Electric Generator: Uses electromagnetic induction to convert mechanical energy to electrical energy.

• Electric Heater: Uses Joule's heating effect of current (\(H = I^2 R t\)).


Step 3: Detailed Explanation:

• Electric Bell: When current flows, an internal coil acts as a temporary magnet (electromagnet) attracting the armature. Thus, it directly uses the magnetic effect of current.

• Electric Motor: Works on the principle that a current-carrying loop experiences torque in a magnetic field. Hence, it utilizes the magnetic effect of current.

• Electric Generator: Works on Faraday's law of electromagnetic induction, which involves changing magnetic fields. Thus, it is intimately linked to magnetic effects.

• Electric Heater: It consists of a high-resistance coil (like Nichrome) which produces heat purely due to the collision of moving electrons with the atoms of the conductor. This is the heating effect of current, not the magnetic effect.


Step 4: Final Answer:
The electric heater does not use the magnetic effect of electric current.