1 Degree Celsius on the Scale of Platinum Resistance Thermometer:
A Platinum Resistance Thermometer (PRT) is a type of temperature sensor that utilizes the change in electrical resistance of platinum wire with temperature. The International Temperature Scale of 1990 (ITS-90) defines the standard platinum resistance thermometer, which is commonly used for precise temperature measurements.

Explanation:
- The Celsius scale is divided into degrees, with each degree representing a specific change in temperature. In the case of a PRT, 1 degree Celsius refers to a change in temperature that causes a corresponding change in the resistance of the platinum wire within the thermometer.

Unsuitability for Measuring Varying Temperature:
While a PRT is highly accurate and provides precise temperature measurements, it is not suitable for measuring rapidly varying temperature. This is due to several reasons:

1. Thermal Inertia:
- The platinum wire used in a PRT has a relatively high thermal inertia, meaning it takes time to respond to changes in temperature.
- This results in a delay between the actual temperature change and the corresponding change in resistance.
- Therefore, the PRT is unsuited for measuring rapid temperature fluctuations as it cannot provide real-time temperature data.

2. Heat Transfer Mechanism:
- The PRT relies on heat transfer mechanisms to measure temperature accurately.
- The time required for heat to transfer from the object being measured to the platinum wire can introduce delays in temperature readings.
- This delay becomes significant when measuring rapidly changing temperatures, leading to inaccurate results.

3. Self-Heating Effect:
- The electrical current passing through the platinum wire generates heat due to its electrical resistance.
- This self-heating effect can cause a temperature rise in the wire, leading to inaccurate temperature measurements.
- When measuring varying temperatures, the self-heating effect becomes more pronounced, making the PRT unsuitable for such applications.

Conclusion:
While a Platinum Resistance Thermometer is highly accurate and precise for measuring temperature, it is not suitable for measuring rapidly varying temperatures due to its thermal inertia, heat transfer mechanisms, and self-heating effects. Other types of thermometers, such as thermocouples or infrared thermometers, are better suited for measuring rapidly changing temperatures in real-time.