Question

Which one of the following works only on D.C. supply?

• A. Electric lamp
• B. Refrigerator
• C. Heater
• D. Electroplating

Hint:

DC Only Applications: ELECTROPLATING, Battery Charging, and Electrowinning require strictly DIRECT CURRENT (DC) to maintain unidirectional ion migration.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Electrochemical deposition and unidirectional current physics: Electroplating (Faraday's laws of electrolysis) requires unidirectional Direct Current (DC) to continuously migrate metal cations to the cathode workpiece; AC current would reverse polarity every half-cycle, alternately depositing and stripping metal with net zero plating.
Key Formula or Approach:
\[ \text{Faraday's Law of Electrolysis: } m = Z \cdot I_{\text{DC}} \cdot t \quad \xrightarrow{\text{AC Supply}} \quad m_{\text{net}} = 0 \implies \mathbf{Requires \text{ } Unidirectional \text{ } DC \text{ } Supply} \]

Step 2: Detailed Explanation:
Comparison of AC vs DC electrical equipment:
1. Electric Lamp (Incandescent) Heater (A, C): Operates on Joule heating ($P = I_{\text{rms}}^2 R$), working equally well on both AC and DC supplies.
2. Refrigerator (B): Driven by single-phase AC induction motors operating on AC supply.
3. Electroplating (D): An electrochemical reduction process where metal cations (e.g., nickel, chromium, copper) in an electrolyte solution are permanently deposited onto a cathode:
- Electroplating works ONLY on Direct Current (D.C.) supply.
- If Alternating Current (AC) were applied, during one half-cycle metal would deposit on the cathode, but during the next half-cycle the reversed polarity would dissolve the deposited metal back into solution, resulting in zero net plating.

Step 3: Final Answer:
Hence, Electroplating works only on D.C. supply, matching option (D).