Chapter 11 – Electromagnetic Waves (Lessons 11.1 & 11.2)

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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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15 Terms

1
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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.

2
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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.

3
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What two physical fields oscillate perpendicular to each other in an electromagnetic wave?

Oscillating electric fields and magnetic fields.

4
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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.

5
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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.

6
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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.

7
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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).

8
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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.

9
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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.

10
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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.

11
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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.

12
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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).

13
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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.

14
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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.

15
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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).