3.3 Electromagnetic Spectrum (Cambridge (CIE) IGCSE Physics)

One possible mnemonic for remembering the electromagnetic spectrum is:

Raging Martians Invaded Venus Using X-ray Guns.

True.

Microwave ovens emit very large amounts of energy, but the energy is prevented from escaping the oven by the metal walls and metal grid in the glass door.

Fluorescence is the process where certain substances absorb ultraviolet light and re-emit it as visible light, causing them to glow.

The main application of radio waves is in wireless communications.

The two main applications of microwaves are:

• heating food

• wireless communications

True.

One application of infrared radiation is night vision cameras.

False.

Infrared and visible light are used in optic fibre communications. Gamma rays are used for sterilising medical equipment and treating cancer.

False.

Sterilising water and detecting fake bank notes are two applications of ultraviolet radiation (UV). X-rays are used for imaging in medicine, dentistry, airport security and industry.

True.

Human eyes can only detect wavelengths of electromagnetic radiation in the visible light section of the electromagnetic spectrum.

False.

Ultraviolet radiation carries too much energy and would be harmful if used for this purpose. Remote controls are one application of infrared radiation.

True.

As the frequency of electromagnetic waves increases, the energy they transfer increases, and therefore so does the danger associated with them.

Ultraviolet, X-rays, and gamma rays can all ionise atoms, which can damage cells and cause mutations, which can lead to cancer.

False.

There are no known harmful effects of radio waves.

True.

Microwaves can be harmful to humans in high levels of exposure, because higher-frequency microwaves cause internal heating.

True.

Mobile phones do emit microwave radiation, but only at low energies which are not known to cause any harm.

True.

Ultraviolet radiation can cause sunburn, eye damage and skin cancer.

True.

X-rays and gamma rays (and UV) are ionising radiation which can remove electrons from atoms, causing damage to DNA which can lead to cell and tissue damage, mutations and cancer.

True.

Sunscreen absorbs ultraviolet light, preventing it from damaging the skin.

True.

The ionising forms of electromagnetic radiation are ultraviolet, X-rays and gamma rays, all of which have higher frequencies than visible light.

False.

The shorter the wavelength (and therefore, the higher the frequency), the more ionising the electromagnetic radiation.

A geostationary satellite is a satellite that orbits above the Earth's equator.

The orbital period of a geostationary satellite is 24 hours.

False.

Geostationary satellites orbit much higher above the Earth's surface than polar satellites do.

The high orbit of geostationary satellites makes them useful for radio and telecommunications broadcasting around the world.

A polar satellite is a satellite that orbits around the Earth's north and south poles.

True.

Polar satellites are also known as low-orbit satellites because they orbit much closer to the Earth's surface than geostationary satellites.

Polar satellites are used for:

• monitoring the weather

• military applications

• taking images of the Earth's surface

Polar satellites have a lower orbit, therefore there is a much shorter time delay between sending and receiving signals, and the images are much clearer. This makes polar satellites more suitable for certain applications including military use.

Microwaves are used for wireless internet (WiFi) because microwaves can penetrate some walls and only require a short ariel for transmission and reception.

Radio waves can pass through walls but the signal is weakened by doing so, therefore radio waves are useful for very short-range communications such as Bluetooth.

True.

The value of analogue signals can vary continuously. They can take any value.

Digital signals can only take discrete states such as:

• 1 and 0

• high and low

• on and off

True.

A digital signal can be regenerated (restored to its original characteristics) so there is minimal noise (unwanted disturbance in the signal). This increases the range of the signal so it can be transmitted over larger distances.