what is meant by a change in temp of 1 degree celcius on the scale of a platinum resistance thermometer
A change in temperature of 1 degree Celsius on the scale of a platinum resistance thermometer refers to the sensitivity of the thermometer. This means that when the temperature increases or decreases by 1 degree Celsius, the resistance of the platinum wire in the thermometer changes by a specific amount.
To understand how this works, it's important to know that platinum has a predictable resistance-temperature relationship. The resistance of a platinum wire changes in a linear manner with temperature. This characteristic is exploited in the design of a platinum resistance thermometer.
To measure temperature using a platinum resistance thermometer, we typically use a Wheatstone bridge circuit. In this circuit, the resistance of the platinum wire is one of the arms of the bridge. As the temperature changes, the resistance of the platinum wire changes as well, causing an imbalance in the bridge circuit. This imbalance can be measured and calibrated to determine the temperature.
Now, coming back to your question, a change in temperature of 1 degree Celsius on the scale of a platinum resistance thermometer means that the resistance of the platinum wire changes by a specific amount for every 1-degree change in temperature. This sensitivity value is typically given by the manufacturer and expressed as "resistance per degree Celsius" or "temperature coefficient." For example, if the temperature coefficient is 0.00385 Ω/°C, it means that the resistance changes by 0.00385 ohms for every 1 degree Celsius change in temperature.
By knowing the temperature coefficient, the change in resistance, and using the Wheatstone bridge circuit, we can calculate the change in temperature based on the change in resistance measured by the thermometer.