In a domestic electric iron, temperature is controlled by:

Explanation:

Temperature Control in Domestic Electric Iron

Definition: In a domestic electric iron, temperature control is a crucial aspect to ensure safe and efficient operation. The temperature is controlled to prevent overheating and to provide the necessary heat for ironing different types of fabrics.

Working Principle: The electric iron uses an electrical heating element, typically made of a high-resistance material such as nichrome, to convert electrical energy into heat. This heating element is connected to a thermostat, which is the primary component responsible for temperature control.

Correct Option Analysis:

The correct option is:

Option 3: Using Thermostat

How a Thermostat Works: A thermostat is a device that automatically regulates temperature. In the context of an electric iron, the thermostat is designed to maintain the iron's temperature within a specific range. It contains a bimetallic strip, which is made of two different metals bonded together. These metals have different coefficients of thermal expansion, causing the strip to bend when heated.

When the iron reaches the set temperature, the bimetallic strip bends enough to open the electrical contacts, cutting off the power supply to the heating element. As the iron cools down, the strip returns to its original shape, closing the contacts and allowing the power to flow to the heating element again. This cycle repeats to maintain a consistent temperature.

Advantages of Using a Thermostat:

• Provides precise temperature control, ensuring the iron operates within safe and effective temperature ranges.
• Prevents overheating, which can damage fabrics and pose a fire hazard.
• Automatically adjusts the power supply to maintain the desired temperature, enhancing user convenience.
• Improves the efficiency and lifespan of the electric iron by preventing excessive wear and tear on the heating element.

Disadvantages:

• Thermostats can wear out over time, requiring replacement to maintain proper temperature control.
• Initial cost of manufacturing may be slightly higher due to the inclusion of the thermostat component.

Applications: Thermostats are widely used in various domestic and industrial heating appliances, including electric irons, ovens, and heaters, to provide reliable and automatic temperature control.

Additional Information

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

Option 1: Controlling Current

This option suggests that temperature control in an electric iron is achieved by controlling the current. While controlling the current can influence the amount of heat generated by the heating element (as power P = I²R), it is not a practical method for precise temperature control in domestic electric irons. Current control would require complex circuitry and would not provide the automatic regulation needed for safe and efficient operation.

Option 2: Controlling Voltage

Controlling the voltage supplied to the heating element can also affect the temperature, as power P = V²/R. However, similar to current control, voltage control is not a practical or efficient method for maintaining a consistent temperature in an electric iron. It would require continuous manual adjustment or complex electronic controls, which are not feasible for simple domestic appliances.

Option 4: Adding Resistance in Series with Heating Element

Adding resistance in series with the heating element can reduce the overall current flow and, consequently, the heat generated. However, this method is not suitable for precise and automatic temperature control. It would require manual adjustments and could lead to inefficient operation and potential safety hazards due to inconsistent temperature regulation.

Conclusion:

The use of a thermostat in domestic electric irons provides a reliable, efficient, and automatic method for temperature control. The thermostat ensures the iron operates within a safe temperature range, preventing overheating and enhancing user convenience. While other methods such as controlling current, voltage, or adding resistance could theoretically influence the temperature, they are not practical or efficient for the precise and automatic regulation required in domestic electric irons. Therefore, the correct option for temperature control in a domestic electric iron is using a thermostat.