GCSE›Edexcel GCSE Physics›Mind mapsSoundEdexcel GCSE Physics: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsThe earSound is a longitudinal wave in airAir vibrations make the eardrum vibrateVibrations pass through tiny bonesWorks over a limited frequency rangeHearing rangeHumans hear about 20 Hz to 20 000 HzUltrasound: above 20 000 HzInfrasound: below 20 HzUsesSonar times reflected ultrasound pulsesFoetal scanning avoids ionising radiationInfrasound explores Earth's coreSonar: 0.4 s at 1500 m/s gives 300 m deepSoundhearing and ultrasoundHzm/sNew mediumSpeed and wavelength changeFrequency stays the sameFrequency is set by the sourceSpeeds up: wavelength increasesSlows down: wavelength decreasesCore practicalSolid: standing wave, ruler between nodesRead frequency from signal generatorFluid: time a known distance, v=xtv = \frac{x}{t}v=txRepeat and average to cut random errorExam tipsUltrasound is above, infrasound belowHalve the distance for an echoMention repeating and averaging