Flashcards · 4PH1 · Topic 3

Waves flashcards

25 cards on Topic 3, subtopics 3a to 3d. Pick a subtopic or study them all.

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Unit of frequency: Hertz (Hz): one wave (oscillation) per second.
Units of wavelength, wave speed and period: Wavelength: metre (m). Wave speed: metre/second (m/s). Period: second (s).
Unit of the angles of incidence, reflection and refraction: Degrees (°), measured from the normal.

Transverse vs longitudinal waves: Transverse: oscillations perpendicular to the direction of travel (light, water waves). Longitudinal: oscillations parallel to the direction of travel (sound).
What do waves transfer?: Energy and information, without transferring matter.
Amplitude and wavefront: Amplitude: the maximum displacement from the equilibrium position. Wavefront: a line joining points on a wave that are in phase.
Wavelength, frequency and period: Wavelength: distance between successive identical points. Frequency: number of waves per second. Period: time for one full oscillation.
A 500 Hz sound wave travels at 340 m/s. Wavelength?: v = fλ, so λ = v/f = 340 ÷ 500 = 0.68 m.
A wave has a period of 0.02 s. Frequency?: f = 1/T = 1 ÷ 0.02 = 50 Hz.
The Doppler effect: Source moving towards you: wavefronts bunch up, wavelength shortens, observed frequency rises. Moving away: wavelength lengthens, frequency falls. A siren sounds higher approaching and lower receding.

Electromagnetic spectrum in order of decreasing wavelength: Radio, microwave, infrared, visible, ultraviolet, x-ray, gamma. Frequency increases along this order.
What do all electromagnetic waves have in common in free space?: They all travel at the same speed (3.0 × 10⁸ m/s). Only frequency and wavelength differ.
Colours of visible light in order of increasing frequency: Red, orange, yellow, green, blue, indigo, violet.
Uses of radio waves, microwaves and infrared: Radio: broadcasting. Microwaves: cooking, communications. Infrared: thermal imaging, remote controls.
Uses of visible light, ultraviolet, x-rays and gamma rays: Visible: photography, optical fibres. Ultraviolet: fluorescent lamps, sterilising. X-rays: medical imaging. Gamma: sterilisation, medical treatment.
Harmful effects of excessive exposure to electromagnetic waves: Microwaves: internal heating of body tissue. Infrared: skin burns. Ultraviolet: damage to surface cells, blindness. Gamma: cancer, mutation.

Law of reflection: Angle of incidence = angle of reflection, both measured from the normal.
Light enters glass from air at an angle. What happens?: It refracts: it slows down and bends towards the normal, so the angle of refraction is smaller than the angle of incidence.
A ray in air meets glass at i = 40° and refracts to r = 25°. Refractive index?: n = sin i / sin r = sin 40° ÷ sin 25° = 0.643 ÷ 0.423 = 1.52.
Critical angle of a material with n = 1.5: sin c = 1/n = 1 ÷ 1.5 = 0.667, so c = 41.8°.
Total internal reflection: when it happens, and two uses: Light travels from a denser to a less dense medium and meets the boundary above the critical angle. Uses: optical fibres; prisms in periscopes and binoculars.
Sound waves: type, and two wave behaviours: Sound waves are longitudinal. They can be reflected and refracted.
Range of human hearing: 20 Hz to 20 000 Hz. (Paper 2 only)
What sets the pitch and the loudness of a sound?: Pitch: frequency (higher frequency, higher pitch). Loudness: amplitude (greater amplitude, louder). (Paper 2 only)
How can a sound wave be displayed and its frequency investigated?: A microphone connected to an oscilloscope displays the waveform; the frequency can be found from the trace. (Paper 2 only)