6 - Waves

• Amplitude: The maximum displacement of a wave from its undisturbed (equilibrium) position
• Angle of Incidence: The angle between the incident ray and normal
• Angle of Reflection: The angle between the reflected ray and normal
• Black: An object will appear black if it absorbs all wavelengths of radiation incident on it
• Colour Filters: Filters that absorb certain wavelengths (colours) and transmit others
• Colour: Colour is determined by frequency and wavelength
• Constant Temperature: A body remains at a constant temperature if it is absorbing radiation at the same rate that it is emitting it
• Convex Lens: A lens that brings parallel rays to focus at the principal focus.The image formed can be either real or virtual
• Wavelength is the distance between the same points on two consecutive waves.
• Diffuse Reflection: Reflection from a rough surface that results in scattering
• Amplitude is the distance from equilibrium line to the maximum displacement (crest or trough).
• Echo Sounding: A technique that uses high frequency sound waves to detect objects in deep water and to measure the depth of water
• Frequency is the number of waves that pass a single point per second.
• Period is the time taken for a whole wave to completely pass a single point.
• Electromagnetic Waves: Transverse waves that transfer energy from the source of the waves, to an absorber
• Focal Length: The distance between the centre of a lens and its principal focus
• Velocity equals frequency times wavelength, represented as 𝑣𝑣 = 𝑓𝑓𝑓𝑓.
• Frequency: The number of waves passing a given point in a second
• Hertz: The unit of frequency
• Period is inversely proportional to frequency, meaning a smaller period results in a higher frequency and greater velocity.
• Human Hearing: Humans can hear sounds in the frequency range of 20Hz to 20kHz
• Transverse waves, such as light or any electromagnetic wave, have peaks and troughs and vibrations are at right angles to the direction of travel.
• Infrared Radiation: A type of radiation that all objects emit and absorb
• Infrared: Used for cooking food, electrical heaters and infrared imaging
• Longitudinal waves, such as sound waves, have compressions and rarefactions and vibrations are in the same direction as the direction of travel.
• Ionising Radiation: Radiation that can cause the mutation of genes and cause cancer
• The hotter the body, the greater the amount of shorter-wavelength radiation released, which are waves with more energy, like x-rays.
• Sun’s energy is mostly absorbed by the earth’s atmosphere, and some is reflected.
• A black body is an object that absorbs all the radiation it receives, does not transmit or reflect any, and therefore also emits all types of radiation.
• The hotter the body, the greater the amount of radiation released per second, making it more powerful.
• The atmosphere is responsible for keeping the earth at a constant temperature by absorbing IR radiation from the sun and trapping IR re-radiated from the Earth.
• Cooling down means energy is being released at a greater rate than it is being absorbed.
• Increasing temperature means a body is absorbing more energy than it emits.
• The amount of energy re-radiated and absorbed leads to Earth’s temperature.
• A body at constant temperature is still radiating and receiving radiation, but it is absorbing radiation at the same rate as it is emitting it.
• The wave moves and not whatever it passes through, for example, a water wave has a moving wave, but the water doesn’t keep moving with it.
• Lens: An object that forms an image through the refraction of light
• Longitudinal Waves: Waves with oscillations that are parallel to the direction of travel/energy transfer
• To measure velocity in sound in air, make a noise at ~50m from a solid wall and record the time for the echo to be heard, then use speed = distance/time.
• Magnification: The ratio of the image height over the object height for a lens