Thermometers which are not kept in touch with the body to measure temperatures are

Options

A. pyrometers
B. thermocouples
C. gas thermometers
D. platinum resistance thermometers

Answer

To solve the question regarding thermometers that do not need to be in contact with the body to measure temperature, we can follow these steps:

### Step 1: Understand the Types of Thermometers
We need to identify different types of thermometers and their working principles. The question provides us with four options:
1. Pyrometers
2. Thermocouples
3. Gas thermometers
4. Platinum resistance thermometers

### Step 2: Analyze Each Option
- **Pyrometers**: These are non-contact thermometers that measure temperature from a distance by detecting the infrared radiation emitted by an object. They are commonly used for measuring high temperatures.

- **Thermocouples**: These require contact with the object to measure temperature. They work based on the thermoelectric effect, where two different metals joined at one end produce a voltage related to temperature difference.

- **Gas Thermometers**: These also require contact with the substance whose temperature is being measured. They operate based on the expansion of gas with temperature changes.

- **Platinum Resistance Thermometers**: These thermometers measure temperature based on the resistance change of platinum with temperature. They also require contact with the object.

### Step 3: Identify the Correct Answer
From the analysis, we see that the only thermometer that does not require contact with the body to measure temperature is the **pyrometer**.

### Conclusion
Thus, the answer to the question is **Pyrometers**.

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