Read Aloud the Text Content

This audio was created by Woord's Text to Speech service by content creators from all around the world.

Text Content or SSML code:

Physics. Topic 5: waves. Wave speed = frequency x wavelength. V=fλ Waves transfer energy in the same direction that they travel. Transverse waves oscillate at right angles to the direction they travel in. they go up and down like curvy line. Longitudinal waves have oscillations along the same line they travel but they have areas of compression where particles are collected together and pushed along the wave. When waves travel through a medium such as air or water, the particles of the medium vibrate and transfer energy between each other, but the overall particles stay in the same place. Representing a wave: A wave can be represented by a set of axis. X-axis is the wavelength, and the y-axis is the amplitude. Wavelength is the distance from the same point on one wave to the next and amplitude is the height from rest point to highest point of the wave. Frequency of the wave is the number of times the wave passes a certain point per second and is measured in hertz. 1 hertz is 1 wave per second. The period of the wave is the amount of time for a full cycle of the wave to be completed, it’s the length of time between one crest passing a point and the next crest passing the same point. Period = 1/frequency. T=1/f. Core practical: measuring speed of water ripples. 1) Set up ripple tank by filling a tray with water and connect dipper to signal generator with a specific frequency. 2) Adjust the height of the wooden rod so that it just touches the surface of the water. 3) Switch on the lamp and motor and adjust until low frequency waves can be clearly observed. 4) Measure the length of a number of waves then divide by the number of waves to record wavelength. It may be more practical to take a photograph of the card with the ruler and take measurements from the still picture. 5) Count the number of waves passing a point in ten seconds then divide by ten to record frequency. 6) Calculate the speed of the waves using: wave speed = frequency × wavelength. Core practical: waves on a string. 1) Attach a string or cord to a vibration generator and use a 200 gram hanging mass and pulley to pull the string taut as shown in the diagram. Place a wooden bridge under the string near the pulley. 2) Switch on the vibration generator and adjust the wooden bridge until stationary waves can be clearly observed. 3) Measure the length of as many half wavelengths as possible, divide by the number of half wavelengths. This is half the wavelength, doubling this gives the wavelength. The frequency is the frequency of the power supply. 4) Calculate the speed of the waves Refraction of waves: Waves travel through different materials and when they arrive, three things can happen. Absorption is where the waves are absorbed by the material which is transferred into the materials energy stores. Reflection is where the waves are bounced back from the material. Transmission is where the waves carry on through the material, but only if it hits straight on. If the wave is at an angle, instead of transmitting it will refract. Core practical: investigating reflection. Get a ray box and shine a ray into a mirror at a measured angle. Mark where the light reflects, and it should equal the angle it was reflected at. Electromagnetic spectrum: The EM spectrum is a continuous spectrum of all possible wavelengths of EM waves. GATE-X USAULLY LETS IN MOST RADIATION is an acronym for the spectrum from highest to lowest frequency. Gamma, x-ray, UV, light, infrared, microwave, radio. Properties of waves: Radio waves use AC current in a circuit which is made up of electrons which produce magnetic and electric fields. Mostly used for communication. Microwaves are used for satellite communication and in microwaves. Infrared is used for heat detection in cameras. Visible light is used in fibre optic cables to send signals via white light. UV is used in sun tanning and can be harmful if exposed to it for long enough which causes cancer. X-rays are used in medical scans by sending the waves through the skin. It works like echolocation by bouncing off of solid objects which can detect breaks or organ damage in the body. Gamma rays are used as tracers since they can be easily tracked it allows for an isotope to be put into the body. Both x-ray and gamma rays cause ionising radiation which is extremely harmful because it can remove electrons from atoms. Visible light is what allows us to see every colour from red to purple. We see colour because the object absorbs the other colour colours so only the reflected ones go into our eyes, and so we register those objects as that colour. Black body radiation: A perfect black body absorbs all forms of EM waves. No radiation is reflected or transmitted but a good absorber is also a good emitter, so black bodies are perfect for emitting radiation. There are no current perfect black bodies, but some are very close to perfect. As the temperature of objects increase, the intensity of wavelengths emitted increases and also the peak wavelength increases. Other waves: Sound waves are longitudinal waves. Sound waves refract as they enter materials however, sound spreads a lot. When sound hits a dense medium, it has to speed up, but its frequency doesn’t change only the wavelength. If speed decreases, wavelength decreases. Ultrasound waves are outside of the human hearing range of 20-20,000 hertz. Ultrasound is produced by some sound waves being reflected instead of refracted which is called partial reflection. When the wave hits an object, there is a delay between the original and reflected sound which is what happens with ultrasound. Can be used for imaging the same way that x-ray works but isn’t harmful to the body. Seismic waves occur during tectonic movement which creates p-waves and s-waves. P-waves are longitudinal so they can travel through solid and liquid. S-waves are transverse and can only travel through solids which makes p-waves faster. When there’s an earthquake, the waves can be recorded with a seismometer which allow seismologists to work out the time for shocks to reach the surface and where the earthquake will and won’t affect. When seismic waves reach the boundary between 2 mediums, it can be absorbed, transmitted, reflected or refracted. Most of the time, they change speed gradually as they go deeper because density of the medium increases which causes a curved path. By measuring where the waves originate from, it allows seismologists to predict where an earthquake will strike to alert authorities on the severity and whether or not they need to evacuate.