AQA GCSE Combined Science Waves PDF

# AQA GCSE Combined Science Waves Knowledge Organiser ## Transverse and Longitudinal Waves ### Wave Properties Waves can be either transverse or longitudinal. * **Transverse wave:** the vibrations of the particles are perpendicular to the direction of energy transfer. The wave has peaks (or cr...

# AQA GCSE Combined Science Waves Knowledge Organiser ## Transverse and Longitudinal Waves ### Wave Properties Waves can be either transverse or longitudinal. * **Transverse wave:** the vibrations of the particles are perpendicular to the direction of energy transfer. The wave has peaks (or crests) and troughs. Examples of transverse waves include water waves and electromagnetic waves. * **Longitudinal wave:** the vibrations of the particles are parallel to (in the same direction as) the direction of energy transfer. A longitudinal wave has areas of compression and rarefaction. Sound waves travelling through air are an example of this type of wave. **Diagram:** * **Peak:** the highest point of a transverse wave. * **Trough:** the lowest point of a transverse wave. * **Amplitude:** the distance from the undisturbed position to the peak or trough of a wave. * **Wavelength:** the distance from a point on one wave to the same point on the next wave. * **Frequency:** the number of waves that pass a given point every second. * **Period:** the time taken for a full wave to pass a given point. **Formulas:** * **Period (T) = 1/frequency (f)** * **Wave speed (v) = frequency (f) * wavelength (λ)** **Explanation:** * When a wave travels through a medium, energy is transferred by the particles but the matter itself does not move. * The speed of a sound wave travelling through the air can be measured using a simple method: A person stands a measured distance from a large flat wall, the person then claps their hands and the time taken to hear the echo is measured. **Remember:** * The distance that the sound wave has travelled will be double the distance between the person and the wall because the wave has travelled to the wall and back again. * It is important to take several measurements and calculate the mean to reduce the effect of human error in your measurements. ### Required Practical: Observing Waves **Aim:** * Identify the suitability of apparatus to measure the frequency, wavelength and speed of waves. **Apparatus:** * Ripple tank * Stroboscope * Metre ruler * White paper **Method:** 1. Set up the apparatus as shown in the diagram. 2. Turn on the power supply and observe the waves produced in the water. 3. To measure the wavelength, use a metre ruler to measure the length of 10 waves and divide this value by 10 to find one wavelength. 4. To measure the frequency, mark a point on the white paper and count the number of waves that pass this point in 10 seconds. 5. To calculate wave speed, use the equation: **Wave speed = frequency * wavelength**. **Waves in a Solid:** * A signal generator can be used to vibrate a string. * The frequency of the signal generator can be adjusted to produce a clear wave pattern. * The wavelength can be measured by counting the number of half wavelengths in a given length of the string. * The wave speed can be calculated using the equation: **Wave speed = frequency * wavelength**. ## The Electromagnetic Spectrum ### Properties of Electromagnetic Waves * Electromagnetic waves are transverse waves. * They transfer energy from a source to an absorber. * All electromagnetic waves travel at the same speed through a vacuum or air. * They are grouped by their wavelength and frequency to form a continuous spectrum. Electromagnetic waves can be reflected, refracted or transmitted through different media. This may change depending on the wavelength, the medium, and the angle of incidence. **Diagram:** * A wave front diagram can be used to show how the wave changes direction as it moves from one medium to another. * The wavelength can be represented by the distance between two peaks or two troughs of the wave. * The frequency can be represented by the number of waves passing a point in a given time. **Explanation:** * When a wave moves from a less dense medium to a more dense medium, it slows down and its wavelength decreases. * The frequency of the wave remains the same. * When a wave moves from a more dense medium to a less dense medium, it speeds up and its wavelength increases. * The frequency of the wave remains the same. ## Required Practical: Radiation and Absorption * Investigate how the nature of a surface affects the amount of infrared radiation absorbed or radiated by that surface. **Aim:** * To find out which type of surface emits the most infrared radiation: * Dark and matt * Dark and shiny * Light and matt * Light and shiny **Apparatus:** * Leslie cube * Infrared detector * Thermometer * Kettle * Heatproof mat **Method:** 1. Place the Leslie cube on a heatproof mat. 2. Boil some water in a kettle, fill the Leslie cube with hot water and put the lid on. 3. Use a thermometer or infrared detector to measure the amount of infrared radiation emitted from one of the surfaces of the Leslie cube. 4. Repeat the experiment for each surface of the Leslie cube, ensuring that the infrared detector is an equal distance from each surface. **Results:** * You should find that a dark, matt surface emits much more infrared radiation than a light, shiny surface. **Explanation:** * Dark, matt surfaces absorb more radiation than light, shiny surfaces, which is why they get hotter in the sun. * Dark, matt surfaces also emit more radiation than light, shiny surfaces, which is why they feel warmer to the touch.