Q: Who discovered infrared (IR) radiation? Q: How did Herschel discover IR radiation? Q: Who discovered ultraviolet (UV) radiation? Q: How did Ritter discover UV radiation? Q: Describe the features of electromagnetic waves. Q: List in order the regions of the continuous electromagnetic spectrum. Q: List in order the colours of the visible light spectrum. Q: Describe how frequency and wavelength changes in the EM spectrum as we move from radio waves to gamma rays.

A: William Herschel (1738-1822). A: In 1800 he was using thermometers to investigate the temperature of the different colours of the visible spectrum (split up using a triangular prism and projected on a sccreen). He found that the temperature increased towards the red end of the spectrum. To his surprise, the hottest part was beyond the red end where there was no visible colour at all. This invisible region is known as the infrared region. A: William Herschel (1738-1822). A: In 1801 he was experimenting with silver chloride (AgCl), which turns black when exposed to sunlight. He placed AgCl in each colour of the visible spectrum. The rate of reaction of AgCl increased from red to violet. He then decided to see what would happen just beyond the violet end of the visible spectrum. The rate of reaction of AgCl was greatest in this invisible region. We know this region as the ultraviolet region. A: Johann Ritter (1776-1810). A: Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. A: All EM waves: are transverse waves; can travel through a vacuum; travel at the same speed of 3 x 108 m/s in air or vacuum; transfer energy; can be reflected, refracted and diffracted; obey the wave equation (v = f x λ). A: Frequency increases and wavelength decreases. A: Red, orange, yellow, green, blue, indigo, violet.

Q: How does the potential danger of EM radiation vary with frequency? Q: What are the harmful effects of microwaves? Q: What are the harmful effects of IR radiation? Q: What are the harmful effects of visible light? Q: What are the harmful effects of UV-A radiation (3.2-4.0 x 10-7 m)? Q: What are the harmful effects of UV-B radiation (2.8-3.2 x 10-7 m)? Q: What is the benefit to life of UV-B radiation (2.8-3.2 x 10-7 m)? Q: What are the harmful effects of UV-C radiation (< 2.8 x 10-7 m)?

A: The potential danger increases as the frequency increases. A: Cause internal heating of body cells (similar to cooking food with microwaves). There have been suggested links with brain tumours, but nothing has been proved. A: The potential danger increases as the frequency increases. A: Intense light can cause permanent damage to the retina. A: Can cause skin burns. A: Causes sunburn. Can cause skin cancer and eye conditions such as cataracts. Can also destroy proteins in the eye lens. A: Causes premature wrinkling of the skin. A: This is the most damaging (ionising); fortunately most is stopped by the ozone layer in the atmosphere. A: Produces vitamin D in the body.

Q: What are the harmful effects of X-rays and gamma rays? Q: What are the uses of long-wave radio waves (1-10 km) and why? Q: What are the uses of medium- and short-wave radio waves (sky waves; 10-100 m) and why? Q: What are the uses of very short-wave radio waves (space waves; 0.1-10 m) and why? Q: Why do you need to be in direct sight of a transmitter to receive TV or FM radio transmissions? Q: What are the uses of microwaves? Q: What are the uses of IR radiation? Q: What are the uses of visible light?

A: Vision, photography, illumination. A: Broadcasting and communications. They can be transmitted from, say, London, and received halfway round the world because long wavelengths bend around the curved surface of the Earth. They also get round around hills, into tunnels etc. A: Can damage the DNA of cells. Can cause cell mutation or destruction. Can trigger cancer. A: Broadcasting, communications and satellite transmissions. They travel in straight lines through the ionosphere to geostationary satellites, from which they are re-transmitted back to Earth. A: Broadcasting an communications. Can be received at long distances from the transmitter because they are reflected off the ionosphere – an electrically charged layer in the Earth’s upper atmosphere, depending on atmospheric conditions and time of day. A: Cooking, communications (e.g. mobile phones) and satellite transmissions. A: The signal cannot bend around hills or travel far through buildings. A: Vision, photography, illumination. A: Cooking, thermal imaging (thermographs), short-range communications (e.g. cordless computer mouse), remote controls, optical fibres, security systems.

Q: What are the uses of UV radiation? Q: What are the uses of X-rays? Q: What are the uses of gamma rays? Q: What is ionisation? Q: When do radioactive sources emit ionising radiation? Q: Which are the ionising radiations? Q: What is the nature of alpha and beta radiation? Q: How is ionising radiation detected?

A: Observing the internal structure of objects, airport security scanners, medical X-rays. A: Security marking, fluorescent lamps, detecting forged bank notes, disinfecting water. A: A process in which radiation transfers some or all of its energy to liberate an electron from an atom. A: Sterilising food and medical equipment, the detection and treatment of cancer. A: Ultraviolet, X-rays, gamma rays, beta particles and alpha particles. A: All the time. A: Using a Geiger-Mϋller (GM) tube. A single alpha or beta particle entering the tube causes the gas atoms inside the tube to ionise. This produces a burst of electrical charge, which is detected by the counter connected to the GM tube. Each ‘clicking sound’ or ‘count’ represents the detection of a single particle. A: Alpha particles (identified by Ernest Rutherford in 1907 as high-speed helium nuclei) and beta particles (identified as high speed electrons in 1898 by Fritz Geisel, Henri Becquerel and Marie Curie).