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15 Question-and-Answer flashcards covering properties, spectrum order, wave behaviour in media, ionising effects, communications, microwave heating, infrared, fibre optics, X-ray and gamma-ray applications, UV uses, and radiation hazards.
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What type of wave are all electromagnetic waves, and what common speed do they share in a vacuum?
All electromagnetic waves are transverse waves that travel at 3 × 10^8 m s⁻¹ in a vacuum.
List the main regions of the electromagnetic spectrum in order from longest wavelength (lowest frequency) to shortest wavelength (highest frequency).
Radio waves → Microwaves → Infrared → Visible light → Ultraviolet → X-rays → Gamma rays.
What two physical fields oscillate perpendicular to each other in an electromagnetic wave?
Oscillating electric fields and magnetic fields.
When an electromagnetic wave passes from a vacuum into a denser medium, how do its speed, wavelength, and frequency change?
Speed and wavelength decrease, but frequency remains the same as at the source.
Why are higher-frequency electromagnetic waves classified as ionising radiation?
Their photons carry enough energy to eject electrons from atoms and molecules, creating ions that can damage living tissue.
Which part of the spectrum is most useful for long-distance radio communication by reflecting off the ionosphere?
Medium/high-frequency radio waves in the 3 – 30 MHz band.
Name two everyday technologies (other than microwave ovens) that use microwaves.
Examples include mobile-phone communication (cellular), Wi-Fi signals, satellite links, radar, and GPS (any two).
Why does food heat up inside a microwave oven?
The oven emits microwaves at a frequency that is readily absorbed by water molecules, increasing their internal energy and thus the food’s temperature.
What property of infrared radiation makes it suitable for remote controls and thermal imaging?
Infrared can be emitted and detected as heat without visible light, allowing contact-less signalling and temperature sensing.
How is visible light employed in fibre-optic telecommunication?
Pulses of light undergo total internal reflection inside optical fibres, carrying large amounts of data over long distances with minimal loss.
State two medical imaging uses of X-rays.
Conventional radiography for detecting fractures or tumours, and Computed Tomography (CT) scans that build detailed cross-sectional and 3-D images.
Give two beneficial applications of ultraviolet (UV) radiation.
Disinfection/sterilisation of water or surfaces, production of vitamin D in the skin, and anti-forgery security features on banknotes (any two).
What is the most common health hazard from over-exposure to ultraviolet radiation?
Sunburn, which can lead to premature skin ageing and an increased risk of skin cancer.
How does ionising electromagnetic radiation damage living cells?
It knocks electrons out of atoms, creating ions that disrupt molecular processes, potentially killing cells or causing mutations and disease.
Which electromagnetic waves are commonly used in radiotherapy to destroy cancer cells, such as in Gamma Knife surgery?
Gamma rays (high-energy X-rays are also sometimes used).