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O-Level Electromagnetic Spectrum
What the O-Level syllabus expects for Electromagnetic Spectrum, and how to practise it.
What the syllabus expects
- State that every electromagnetic wave is transverse and travels through a vacuum at the same speed.
- Describe the spectrum's main regions arranged by wavelength and frequency.
- Give typical uses for each spectrum region: radio waves (such as radio and TV communications, astronomy, and RFID tags); microwaves (such as mobile phones, microwave ovens and satellite television); infrared (such as remote controllers, intruder alarms and thermal imaging); visible light (such as photography, and optical fibres in medicine and telecommunications); ultraviolet (such as sunbeds, bank note authentication and disinfecting water); X-rays (such as medical radiology, security screening, and spotting defects in industry); gamma rays (such as sterilising food, and detecting and treating cancer).
- Describe the hazardous effects that over-exposure to electromagnetic waves, such as heating and ionising effects, can have on living cells and tissue.
How it's examined
Questions on this topic most often ask you to state. About 2% of the past-paper style questions in Rae's bank for this subject sit in this topic.
Worked examples
Example 1 (4 marks)
A transmitter on Earth broadcasts television signals whose frequency is 6000 MHz. Give the speed of electromagnetic waves through a vacuum, then work out the signal's wavelength.
Show the worked answer
Step 1 - state the speed. All electromagnetic waves travel through a vacuum at the same speed, the speed of light: c = 3 × 10⁸ m/s (300 000 000 m/s). Step 2 - convert the frequency into hertz, the SI unit, before using it in any formula. 1 MHz (megahertz) = 1 × 10⁶ Hz, so f = 6000 MHz f = 6000 × 10⁶ Hz f = 6 × 10³ × 10⁶ Hz f = 6 × 10⁹ Hz Step 3 - state the wave equation, which links speed, frequency and wavelength for ANY wave. v = fλ where v is the wave speed (m/s), f the frequency (Hz) and λ the wavelength (m). Step 4 - rearrange it to make λ the subject. Divide both sides by f: λ = v/f Step 5 - substitute the values, keeping the powers of ten separate from the digits. λ = (3 × 10⁸ m/s) / (6 × 10⁹ Hz) λ = (3/6) × 10⁸⁻⁹ m λ = 0.5 × 10⁻¹ m λ = 0.05 m So the wavelength of the television signal is 0.05 m, that is 5 cm.
More O-Level Pure Physics topics
Physical Quantities, Units and Measurement · Kinematics · Dynamics · Turning Effects of Forces · Pressure · Energy · all of O-Level Pure Physics