Question

Explain with justification two uses of each of two following as an electrical conductor:
(i) Brass (ii) Silver

Answer 1

(i) Brass

Brass is an alloy primarily made of copper and zinc. While it is a good electrical conductor, it is not as conductive as pure copper. Its usefulness comes from a combination of its conductivity with other superior mechanical and chemical properties.

Use 1: Electrical Plugs, Sockets, and Terminals

• Explanation: The pins of electrical plugs, the contact points inside wall sockets, and the screw terminals used to connect wires are very commonly made of brass.
• Justification:
  1. Durability and Hardness: Pure copper is relatively soft and can easily bend or deform. Plugs and sockets are subjected to repeated insertion and removal, which is significant mechanical stress. Brass is much harder and more durable than pure copper, so it can withstand this wear and tear without deforming, ensuring a safe and reliable connection over time.
  2. Corrosion Resistance: When exposed to air and moisture, copper tarnishes (oxidizes) relatively quickly. This layer of oxide is less conductive and can lead to a poor connection, overheating, and a potential fire hazard. Brass is significantly more resistant to corrosion and tarnishing, maintaining a clean, low-resistance contact surface for much longer. The slight decrease in conductivity compared to pure copper is a worthwhile trade-off for this vast improvement in durability and safety.

Use 2: Lamp Holders and Switch Components

• Explanation: The threaded socket in a standard light bulb holder (e.g., an E27 or B22 base) and the internal moving contacts in many electrical switches are made from brass.
• Justification:
  1. Machinability: Brass is an exceptionally easy metal to machine. This means it can be precisely and economically cut, drilled, and threaded to create the complex shapes required for switch mechanisms and screw-in lamp holders. This property lowers manufacturing costs.
  2. Hardness and Low Friction: In a switch, the contacts must slide or press against each other reliably thousands of times. Brass provides a hard, smooth surface that resists wear from this repeated mechanical action. Its properties ensure the switch operates smoothly and maintains good electrical contact throughout its lifespan.

---

(ii) Silver

Silver (Ag) is a precious metal that has the highest electrical conductivity of all metals, even higher than copper. Its use is limited by its high cost, but it is essential in applications where performance is critical.

Use 1: High-Quality Electrical Contacts and Relay Points

• Explanation: Silver is used for the contact points in high-performance switches, circuit breakers, and electromagnetic relays (devices that use an electromagnet to operate a switch).
• Justification:
  1. Highest Electrical Conductivity: When a switch or relay closes, the current must pass through a very small point of contact. Any resistance at this point (contact resistance) will cause heat generation and a voltage drop. Silver's supreme conductivity minimizes this resistance, allowing for maximum current flow with minimal heat loss. This is critical in high-power or sensitive electronic circuits where efficiency and reliability are paramount.
  2. Resistance to Oxidation: While silver does tarnish by reacting with sulfur in the air (forming silver sulfide), it is highly resistant to normal oxidation (forming an oxide layer). Importantly, silver oxide is still electrically conductive, unlike the insulating copper oxide. This means that even with some surface degradation, a silver contact will continue to function reliably as a conductor.

Use 2: Plating for High-Frequency Conductors (Skin Effect)

• Explanation: In very high-frequency applications, such as in radio frequency (RF) circuits, waveguides, and high-end audio/video cables, copper conductors are often plated with a thin layer of silver.
• Justification:
  1. The Skin Effect: At high frequencies, electrical current does not flow through the entire volume of a conductor. Instead, it concentrates on the outer surface or "skin." The higher the frequency, the thinner this skin becomes.
  2. Optimizing Performance and Cost: Since the current is only flowing on the surface, the conductivity of the core material (like copper) becomes irrelevant. By plating the copper with a thin layer of silver, the conductor behaves as if it were made of solid silver from the perspective of the high-frequency current. This provides the ultimate performance of silver (lowest possible signal loss) while keeping the cost much lower than using a solid silver conductor.