Higher
Answer
Flashcards · J249 · Topic 5
Waves in matter flashcards
34 cards on Topic 5, subtopics P5.1 to P5.3. Pick a subtopic or study them all.
Study mode needs JavaScript. Every card is listed below, so you can still cover the answers and test yourself.
Choose your cards
Session complete
Worth another look:
All 34 cards
For a quick read-through or printing. Cover the right-hand side to test yourself. Cards marked Higher are Higher tier content only.
P5.1 Wave behaviour
- Amplitude and wavelength
- Amplitude: the maximum displacement from the rest position. Wavelength: the length of one complete wave, for example crest to crest.
- Frequency and period
- Frequency: waves passing a point per second (Hz). Period: time for one complete wave (s). T = 1 ÷ f.
- Wave speed equation
- v = f × λ (m/s, Hz, m)
- A note of 850 Hz travels in air at 340 m/s. Its wavelength?
- λ = 340 ÷ 850 = 0.40 m
- Transverse vs longitudinal waves
- Transverse: vibrations at right angles to the direction of travel, with crests and troughs (ripples). Longitudinal: vibrations along it, with compressions and rarefactions (sound in air).
- Evidence that a wave, not the medium, travels
- A floating cork bobs up and down in the same spot as ripples pass. A wave transfers energy, not matter.
- Measuring the speed of sound with an echo
- Time the echo from a wall a distance d away. The sound travels there and back, so v = 2d ÷ t. Use an electronic timer for short times.
- Sound passes from air into water. What happens to its frequency, speed and wavelength?
- Frequency stays the same (set by the source). Speed increases, so wavelength increases in proportion.
- A 640 Hz note passes from air (340 m/s) into water (1480 m/s). Wavelength in each?
- Air: 340 ÷ 640 = 0.53 m Water: 1480 ÷ 640 = 2.3 m
- A sonar echo returns from the seabed after 0.68 s (speed in water 1500 m/s). Depth?
- 1500 × 0.68 = 1020 m there and back, so the depth is 510 m.
- Ultrasound, and how it makes an imageHigher
- Sound above the upper limit of human hearing (above 20 kHz). Pulses are partly reflected at boundaries between tissues, and the echo timing builds an image.
- How the ear converts sound into nerve signalsHigher
- Eardrum vibrates → three small bones pass the vibration on → cochlea (fluid-filled) → hair cells produce electrical signals → auditory nerve to the brain.
- Human hearing range, and why any hearing range is limitedHigher
- Roughly 20 Hz to 20 kHz (the upper limit falls with age). Vibrating parts have mass and stiffness, so outside a range they cannot follow the pressure changes.
P5.2 The electromagnetic spectrum
- Properties shared by all electromagnetic waves
- Transverse; travel through a vacuum; all travel at the same speed in a vacuum (3.0 × 10⁸ m/s); transfer energy from a source to an absorber.
- Order of the electromagnetic spectrum, long wavelength to short
- Radio, microwave, infrared, visible, ultraviolet, X-rays, gamma rays. This is also low frequency to high frequency.
- A microwave signal has frequency 10 GHz. Wavelength? (c = 3.0 × 10⁸ m/s)
- λ = 3.0 × 10⁸ ÷ 1.0 × 10¹⁰ = 0.030 m
- What part of the spectrum can the eye detect?
- Only visible light, about 400 nm (violet) to 700 nm (red). Red has the longest wavelength and lowest frequency of visible light.
- One use each of radio, microwaves, infrared and ultraviolet
- Radio: broadcasting radio and TV. Microwaves: satellite links, mobile phones, cooking. Infrared: remote controls, heaters, thermal imaging. Ultraviolet: security marking, sterilising water.
- One use each of X-rays and gamma rays
- X-rays: imaging bones and teeth, baggage scanners. Gamma rays: sterilising equipment and food, cancer treatment, medical tracers.
- Hazards of ultraviolet, X-rays and gamma rays
- Ultraviolet: sunburn, skin ageing, skin cancer, eye damage. X-rays and gamma: ionising, so they damage cells and DNA and can cause cancer.
- How are radio waves transmitted and received?Higher
- Alternating current makes electrons in the transmitting aerial oscillate, giving radio waves of the same frequency. In a receiving aerial the waves make electrons oscillate, producing an alternating current of the same frequency.
- Three differences between materials that waves use to detect hidden structuresHigher
- Different wave speeds, different amounts of absorption, and reflection at boundaries.
- How does an X-ray image show a broken bone?Higher
- Bone absorbs X-rays more than soft tissue does, so the bone shows as a shadow on the detector.
P5.3 Wave interaction
- Four things that can happen to a wave at a boundaryHigher
- Absorbed, transmitted, reflected or refracted. Which happens depends on the substance and the wavelength.
- What causes refraction?Higher
- A change in wave speed. One end of the wavefront enters the new substance first and changes speed while the other end is still at the old speed, so the wavefront turns.
- Which way does a ray bend entering a medium where it travels more slowly?
- Towards the normal. Entering a faster medium it bends away from the normal; along the normal it does not bend.
- Light enters water. What happens to its frequency and wavelength?Higher
- The frequency stays the same. The speed falls, so the wavelength gets shorter in the same proportion.
- Light through a parallel-sided glass block
- The emergent ray is parallel to the incident ray but shifted sideways.
- Convex vs concave lens
- Convex: thicker in the middle; converges parallel rays to the principal focus; can form a real image. Concave: thinner in the middle; diverges rays; image always virtual, upright and smaller.
- Image formed by a convex lens when the object is beyond 2F, between F and 2F, and inside F
- Beyond 2F: real, inverted, smaller. Between F and 2F: real, inverted, larger. Inside F: virtual, upright, larger.
- Primary and secondary colours of light
- Primary: red, green, blue. Red + green = yellow; green + blue = cyan; red + blue = magenta.
- What do a coloured filter and an opaque coloured object do to light?
- A filter transmits its own colour and absorbs the others. An opaque object reflects its own colour and absorbs the rest. Neither adds colour.
- A green leaf is seen in red light. What colour does it look?
- Black. It reflects only green, and there is no green in red light.
- Specular reflection vs scattering
- Specular: from a smooth surface; parallel rays stay parallel, so you see an image. Scattering: from a rough surface; rays leave in many directions.