Problem 81 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following alloy is used for making magnets for hearing aids? (a) invar (b) german silver (c) monel metal (d) alnico

Step-by-Step Solution

Answer

The alloy used for making magnets in hearing aids is 'alnico'.

Step 1: Understanding the Problem

We need to determine which alloy is used for making magnets in hearing aids. An alloy is a mixture of metals, and different alloys have varying properties, making some more suitable for specific applications than others.

Step 2: Analyzing Each Option

Let's examine the properties of each option: (a) 'Invar' is known for its low coefficient of thermal expansion, primarily used in precision instruments. (b) 'German silver' is a corrosion-resistant alloy but is used in musical instruments and cutlery. (c) 'Monel metal' is strong and corrosion-resistant, often used in marine applications. (d) 'Alnico' is known for its strong magnetic properties, used in magnets.

Step 3: Selecting the Most Suitable Alloy

Based on our analysis, 'alnico' is designed specifically for strong magnetic properties, making it ideal for use in creating magnets. Hearing aids require magnets, which aligns with the use of 'alnico'.

Key Concepts

Alnico

Alnico is a type of alloy containing aluminum (Al), nickel (Ni), and cobalt (Co), along with elements like iron and copper. This combination of metals creates a material that exhibits excellent magnetic properties. Alnico magnets are known for their strength and ability to retain magnetism, making them perfect for applications where consistent magnetic performance is crucial.

Apart from hearing aids, where strong, small magnets are essential, alnico is also utilized in various devices and instruments.

• Guitar pickups
• Microphones
• Motors
• Scientific instruments

The unique blend of metals provides alnico with excellent temperature stability, allowing it to function effectively in environments that undergo temperature fluctuations. This stability is vital in devices that generate heat or operate in variable climate conditions.

Magnetic Properties of Alloys

Alloys like alnico have specific magnetic properties that make them suitable for various technological applications. The primary attribute of magnetic alloys is their ability to be magnetized and to retain this magnetism over time. Alnico stands out due to its:

• Remanence: It refers to the residual magnetism the material can exhibit after the external magnetic field is removed. Alnico has high remanence, allowing it to sustain a magnetic field when needed.
• Coercivity: This property indicates the resistance to demagnetization. Alnico's moderate coercivity means it can resist demagnetization fairly well, though advancements have led to developments of other materials with even higher coercivity.
• Permeability: This is the ease with which a material can be magnetized. Alnico has excellent permeability, which makes it easily magnetizable.

These properties are crucial as they define how an alloy will perform in magnetic applications, such as in hearing aids where maintaining a stable magnetic field is important for performance.

Uses of Alloys in Technology

Alloys play an essential role in modern technology due to their enhanced properties, specifically tailored for particular applications. Alnico is just one example, showcasing the utility of alloys in technological advancements. Here are some common uses of alloys in technology:

• Magnet Production: Alloys like alnico and neodymium are pivotal in producing powerful and efficient magnets used in various electronic devices.
• Construction Materials: Alloys such as steel and duralumin provide strength and durability, essential for buildings, vehicles, and aircraft.
• Electronics: Copper-nickel alloys are extensively used in electronic and thermal devices due to their excellent conductivity and resistance to corrosion.
• Jewelry and Decorations: Alloys like gold-palladium are used in jewelry for their aesthetic value and working properties.

By combining different metals, alloys are engineered to provide customized performance traits such as increased strength, ductility, or corrosion resistance. This makes them indispensable across numerous fields of technology, enhancing both functionality and longevity of products.