Understanding Magnets for Lifting Heavy Loads

The question asks about the type of magnet used specifically for lifting and transporting heavy metallic objects like big metals, steel girders, and scrap iron. This requires a magnet that can be very strong when needed and can also release the load when required. Let's look at the types of magnets mentioned in the options.

We are given the following options:

• Electromagnet
• Diamagnet
• Permanent magnet
• Paramagnet

Properties of Different Magnet Types

Let's briefly examine the properties of each type of magnet:

Electromagnet:

• An electromagnet is a type of magnet where the magnetic field is produced by an electric current.
• It is usually made by coiling wire around a ferromagnetic core (like iron).
• The magnetism is present only when the electric current flows through the coil.
• The strength of the magnetic field can be controlled by varying the current or the number of turns in the coil.
• Crucially, the magnetism can be switched on and off by controlling the electric current.

Permanent magnet:

• A permanent magnet is a material that retains its magnetic properties even after the external magnetic field is removed.
• These magnets always have a magnetic field around them.
• Their magnetic strength is generally fixed (unless subjected to extreme conditions).
• They cannot be easily switched on or off.

Diamagnet:

• Diamagnetic materials create an induced magnetic field in opposition to an externally applied magnetic field.
• They are weakly repelled by strong magnets.
• They are not used for attracting ferromagnetic materials like iron for lifting.

Paramagnet:

• Paramagnetic materials are weakly attracted by an externally applied magnetic field.
• They do not retain their magnetic properties when the external field is removed.
• Their magnetic effect is much weaker than that of ferromagnetic materials used in electromagnets.

Why Electromagnets are Used for Lifting Heavy Loads

For lifting heavy loads of metal like steel girders and scrap iron, two main features are essential:

1. The magnet must be strong enough to lift very heavy weights.
2. The magnet must be able to release the load at the desired location.

Electromagnets can be designed to produce extremely strong magnetic fields, far stronger than typical permanent magnets, making them capable of lifting heavy industrial loads. More importantly, because their magnetism is controlled by an electric current, the magnetic field can be turned off simply by switching off the power supply. This allows the lifted objects to be released easily and precisely.

Permanent magnets are always magnetic and cannot release the load on demand. Diamagnetic and paramagnetic materials are weakly magnetic (diamagnetic repel, paramagnetic weakly attract) and are not suitable for lifting heavy ferromagnetic materials.

Therefore, the ability to generate strong magnetic fields and the crucial feature of being able to switch the magnetism on and off makes the electromagnet the ideal choice for lifting and transporting heavy loads like big metals, steel girders, and scrap iron objects in industrial applications.