What are ultraviolet radiations ? How are they detected ? State one use of these radiations

Explanation

### Step-by-Step Solution

1. **Definition of Ultraviolet Radiations:**
- Ultraviolet radiations, commonly known as UV rays, are a type of electromagnetic radiation. They have wavelengths ranging from 100 angstroms (10^-9 meters) to 4000 angstroms (4 x 10^-7 meters). This range places them between visible light and X-rays on the electromagnetic spectrum.

2. **Detection of Ultraviolet Radiations:**
- UV rays are not detectable by the human eye, meaning we cannot see them directly. However, they can be detected through their interaction with certain materials. When UV rays strike specific substances, they can cause fluorescence, which is the emission of light at a longer wavelength (lower energy) than the original UV radiation. This emitted light is often in the violet region of the visible spectrum, which can be seen by the human eye.

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