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# Science P1 Topic 4

### GCSE edexcel core science physics: waves and the earth

What range of frequency is infrasound? Frequencies less than 20 Hz
What are the uses of infrasound? * Communication between animals * Biologists can use microphones that detect infrasound to study the movement of those animals in remote locations * The detection of volcanic eruptions in remote areas * Studying the passage of meteors in the atmosphere
What are the two equations for the speed of a wave? 1. wave speed(m/s)=distance(m)/time(s) 2. wave speed(m/s)=frequency(Hz)x wavelength(m)
What range of frequency is ultrasound? Frequences more than 20000 Hz- above the audible range
What are the uses of ultrasound? * Sonar (animals making ultrasound waves and waiting for them to be reflected to detect obstacles in their path) * Sonar for humans- detecting how far a boat is from the sea bed, etc. * Foetal scanning * Communication between animals
How do you calculate depth/distance with ultrasound? distance(m) = speed(m/s) x time (s) then divide the distance by two
How far is a boat from the sea bed if the sound wave travels at 1000 m/s and takes 3.5 seconds? distance(m) = 1000m/s x 3.5s = 3500 3500/2 = 1750m
How are seismic waves produced? By earthquakes or explosions
What is the difference between the focus and epicentre? The focus is the centre of the earthquake- where the the rock suddenly moves or fractures, causing the earthquake. The epicentre is the point on the earth's surface above the focus.
What are some features of P waves? (wave type, what they can travel through, speed, amplitude etc) WAVE TYPE: longitudinal WHAT THEY CAN TRAVEL THROUGH: solids and liquids (crust, mantle and core) SPEED: faster than s waves AMPLITUDE: smaller than s waves
What are some features of S waves? (wave type, what they can travel through, speed, amplitude etc) WAVE TYPE: transverse WHAT THEY CAN TRAVEL THROUGH: solids only SPEED: slower than p waves AMPLITUDE: larger than p waves
What causes refraction of seismic waves? - The properties of rock change with depth, so the path of the wave bends gradually - When the wave suddenly travels into a new type of rock, refraction occurs and send the wave in a completely different direction
What causes reflection of seismic waves? Some energy is reflected when a wave reaches a boundary between different types of rock.
How are earthquakes caused? Convection currents in the mantle cause the tectonic plates move. If the currents push two plates right past each other, friction builds up & stops the plates moving. When enough pressure builds to overcome the friction, the plates move with a sudden jerk
Why is it difficult to predict earthquakes and tsunamis? Because although scientists can work out where earthquakes may occur (at plate boundaries), they can't measure the forces or friction between the plates- meaning its difficult to predict when movement will happen
What is a seismometre? An instrument that can detect seismic waves
How can you work out how far away the earthquake has happened using the seismometre? By measuring the time difference bweten the arrival of the faster P waves and slower S waves
What is triangulation? Where you use at least three seismometres in different areas to pick up the seismic waves- then work out the difference in the arrival of the P and S waves for all of them. Draw circles, and where they all overlap is where the epicentre is.
Why do scientists not know whether a tsunami will happen by looking at seismometre traces? Because they don't show the pressure of the oceans- whereas tsunami detectors do.
Created by: 11043

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