# Electromagnetic radiation (UV, X-rays, gamma)

> The family of light, and why UV harms the skin


## Objectives

- Name the members of the electromagnetic spectrum in order: radio, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays.
- State that energy increases from radio waves to gamma rays, as the wavelength gets shorter.
- Explain why UV rays can damage the skin although we cannot see them.

## 1. Electromagnetic radiation (UV, X-rays, gamma): from zero




## 2. Burnt, but not hot

Predict: what burns the skin?

- Bright visible light
- Heat (infrared) from the Sun
- Ultraviolet (UV) rays from the Sun ✓

Sunburn comes from ultraviolet (UV) rays from the Sun: they are invisible and carry more energy than visible light, and they still reach you on a cloudy day.

[ar-EG] حرق الشمس سببه الـ ultraviolet (UV) rays اللي جاية من الشمس: مش بتتشاف، وفيها energy أكتر من الـ visible light، وبتوصلك حتى في يوم غيم.
## 3. A family of waves

Electromagnetic radiation Waves that carry energy at the speed of light, even through empty space. The electromagnetic spectrum: radio, microwaves, infrared, visible, UV, X-rays, gamma rays Light is not the only electromagnetic radiation: radio waves, X-rays and gamma rays are too. Our eyes see only the visible part. In empty space, all of them travel at the same speed. They differ in wavelength. Shorter wavelength means higher frequency and more energy.


## 4. Walk along the spectrum

Slide from radio waves to gamma rays. Read what each one does. Position in the spectrum (1 = radio, 7 = gamma) Energy rank (1 = lowest) Radio waves Longest wavelength, lowest energy. They carry radio and TV signals. Microwaves Shorter waves than radio. Used in microwave ovens and mobile phone signals. Infrared Less energy than visible light. We feel it as heat, from the Sun or a hot stove. Visible light The only part our eyes can see, from red to violet. Ultraviolet (UV) More energy than visible light. It can burn and damage the skin. Sunscreens are made to block it. X-rays More energy than UV. They pass through skin, but less through bone, so they give X-ray images. Gamma rays The shortest wavelength: the highest energy and the highest penetrating power. Gamma rays are tiny particles.


## 5. Invisible is not weak

UV is invisible, so it must be weak. Infrared Invisible. **Less** energy than visible light. We feel it only as warmth. Ultraviolet (UV) Invisible. **More** energy than visible light. It can burn the skin.


## 6. Sort and apply

A hospital image shows bones through the skin. Compared with UV, the rays used have:

- a longer wavelength and more energy
- the same energy, because all these rays have the same speed
- less energy, because they pass through gently
- more energy and a shorter wavelength ✓

Rays that show bones through the skin are X-rays. They have a shorter wavelength than UV, so they carry more energy and pass through the body more easily.

[ar-EG] الأشعة اللي بتورّي العضم من خلال الجلد هي الـ X-rays. الـ wavelength بتاعتها أقصر من الـ UV، فالـ energy بتاعتها أكتر وبتعدّي من الجسم أسهل.
## 7. Summary

Electromagnetic radiation: radio, microwaves, infrared, visible, ultraviolet (UV), X-rays, gamma rays. Light is only one member. From radio to gamma: the wavelength gets shorter and the energy gets higher. UV has more energy than visible light, so it can damage the skin. Gamma rays are electromagnetic waves with the highest energy and the highest penetrating power. Key words: **UV**, **X-rays**, **gamma rays**, **more energy**, **high penetrating power**. Next: which compound of titanium protects the skin from UV? Can you explain why UV burns the skin, although infrared feels warmer? UV has a shorter wavelength than visible light, so it carries more energy and can damage the skin. Infrared has less energy than visible light: we feel it only as warmth.



Chapter: Transition Elements (https://yaani.ai/ar/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/ar/lesson/chem-s3-en.lesson-phys.em-spectrum