The two basic forms of moving-iron type voltmeters and ammeters are:

Explanation:

Moving-Iron Type Voltmeters and Ammeters

Definition: Moving-iron instruments are a class of electrical measuring devices used to measure voltages (voltmeters) and currents (ammeters). These instruments operate on the principle of electromagnetic force acting on a soft iron piece that moves when subjected to a magnetic field generated by the current or voltage.

Types: The two basic forms of moving-iron type instruments are:

• Attraction Type: In this type, a piece of soft iron is attracted towards a coil carrying the current or voltage, causing a deflection of the pointer on the calibrated scale. The amount of deflection is proportional to the current or voltage being measured.
• Repulsion Type: This type involves two pieces of soft iron placed near a coil. When current flows through the coil, both pieces of iron become magnetized with like polarities, resulting in a repulsive force between them. This force moves one of the iron pieces, which is connected to the pointer, causing a deflection on the scale proportional to the measured quantity.

Working Principle:

The working of moving-iron instruments is based on the magnetic field produced by the current or voltage in a coil. When a soft iron piece is placed in the vicinity of this magnetic field, it experiences either an attractive or repulsive force, depending on the type of moving-iron instrument. The resulting mechanical motion is converted into an angular deflection of the pointer over a calibrated scale.

Advantages:

• Moving-iron instruments can measure both AC and DC quantities, making them versatile for various applications.
• They are robust and can withstand overloads to a certain extent.
• They are relatively simple in construction and cost-effective.

Disadvantages:

• The scale of moving-iron instruments is non-linear, especially at lower ranges, making precise readings difficult in some cases.
• They are prone to errors caused by stray magnetic fields and temperature variations.
• Friction in the moving parts can affect the accuracy of the readings.

Applications:

• Used in power systems for monitoring current and voltage levels.
• Suitable for general-purpose measurements in laboratories and industries.
• Commonly employed in switchboards and distribution panels.

Correct Option Analysis:

The correct option is:

Option 2: Attraction type and Repulsion type

This option correctly identifies the two basic forms of moving-iron instruments. The attraction type involves the movement of a soft iron piece towards the coil due to magnetic attraction, while the repulsion type involves the repulsive force generated between two magnetized soft iron pieces. Both these types are widely used in the design of moving-iron voltmeters and ammeters, leveraging their simplicity and robustness for measuring electrical quantities.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Permanent magnet type and electrodynamic type

This option is incorrect because permanent magnet and electrodynamic types are not related to moving-iron instruments. Permanent magnet instruments (e.g., PMMC) use a permanent magnet and are primarily used for DC measurements. Electrodynamic instruments, on the other hand, use two coils (fixed and moving) and are suitable for AC and DC measurements, but they do not fall under the category of moving-iron instruments.

Option 3: Induction type and electrostatic type

This option is also incorrect. Induction type instruments work on the principle of electromagnetic induction and are typically used for measuring AC quantities, such as in energy meters. Electrostatic type instruments, on the other hand, measure voltage using the electrostatic force between two plates. Neither of these types is related to moving-iron instruments.

Option 4: Split-phase type and shaded-pole type

This option is incorrect as it refers to types of single-phase AC motors, not electrical measuring instruments. Split-phase and shaded-pole designs are used in small electric motors, such as those found in household fans or appliances, and have no connection to moving-iron voltmeters or ammeters.

Option 5:

There is no option 5 provided in the question, so it does not apply to the evaluation.

Conclusion:

The moving-iron type instruments are widely used for their versatility and simplicity. Understanding their two basic forms, attraction type and repulsion type, is crucial for their application in various electrical measurement tasks. While the other options describe different types of instruments or devices, they are not related to the moving-iron type voltmeters and ammeters. By leveraging the principles of electromagnetic force, these instruments provide reliable and robust solutions for measuring both AC and DC electrical quantities.