Edexcel IGCSE Physics 复习笔记 3.1.7 Dangers of EM Waves

• As the frequency of electromagnetic (EM) waves increases, so does the energy
• Beyond the visible part of the spectrum, the energy becomes large enough to ionise atoms
• As a result of this, the danger associated with EM waves increases along with the frequency
  • The shorter the wavelength, the more ionising the radiation
  • Although the intensity of a wave also plays a very important role

   

Ultraviolet, X-rays and gamma rays can all ionise atoms

• In general, electromagnetic waves become more dangerous the shorter their wavelength
  • For example, radio waves have no known harmful effects whilst gamma rays can cause cancer and are regarded as extremely dangerous

   

• Because of ionisation, ultraviolet waves, X-rays and gamma rays can have hazardous effects on human body tissue
  • The effects depend on the type of radiation and the size of the dose

   

• They can damage cells and cause mutations, making them cancerous

• The main risks associated with electromagnetic waves are summarised in the table below:

Dangers of EM Waves Table

Microwaves

• Certain frequencies of microwaves are absorbed by water molecules
• Since humans contain a lot of water, there is a risk of internal heating from microwaves
• This might worry some people, but microwaves used in everyday circumstances are proven to be safe
  • Microwaves used for communications (including mobile phones) emit very small amounts of energy which are not known to cause any harm
  • Microwave ovens, on the other hand, emit very large amounts of energy, however, that energy is prevented from escaping the oven by the metal walls and metal grid in the glass door

   

Ultraviolet

• Ultraviolet is similar to visible light, except it is invisible to the human eye and carries a much higher energy
• If eyes are exposed to high levels of UV it can cause severe eye damage
  • Good quality sunglasses will absorb ultraviolet, preventing it from entering the eyes

   

• Ultraviolet is ionising meaning it can kill cells or cause them to malfunction, resulting in premature ageing, and diseases such as skin cancer
  • Sunscreen absorbs ultraviolet light, preventing it from damaging the skin

   

X-rays & Gamma Rays

• X-rays and gamma rays are the most ionising types of EM waves
  • They are able to penetrate the body and cause internal damage
  • They can cause the mutation of genes and cause cancer

   

• Fortunately, the level of X-rays used in medicine is kept to minimum levels at which the risk is very low
  • Doctors, however, will leave the room when taking X-rays in order to avoid unnecessary exposure to them

   

• People working with gamma rays have to take several precautions to minimise their exposure and are routinely tested to check their radiation dose levels
• For example, radiation badges are worn by medical professionals such as radiographers to measure the amount of radiation exposure in their body

Radiation badges are used by people working closely with radiation to monitor exposure

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