Waves and the Electromagnetic Spectrum
- Created by: Former Member
- Created on: 19-09-19 07:41
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- Section 18 - Waves and the Electromagnetic Spectrum
- Wave Basics
- Particles vibrate to transfer energy when waves travel through mediums
- Amplitude = distance from rest line to crest/trough
- Wavelength = length of a full cycle
- Frequency = number of complete cycles passing a point in a second
- Period = number of seconds for one full scyle
- tranverse waves have perpendicular vibrations
- longitudinal waves have parallel vibrations
- wave speed is distance divided by time or frequency multiplied by wavelength
- Measuring Waves
- Use an oscilloscope to measure the speed of sound
- set up a speaker and oscilloscope, slowly move microphones apart until one wavelength
- measure for wavelength and use frequency set by signal generator to find speed
- set up a speaker and oscilloscope, slowly move microphones apart until one wavelength
- Measure speed of water ripples with a strobe light
- signal generator attached to a dipper, turn on strobe light and alter frequency until shadows appear to freeze
- measure distance 10 wavelengths apart then find average to calculate speed
- signal generator attached to a dipper, turn on strobe light and alter frequency until shadows appear to freeze
- Use peak frequency to find the speed of waves in solids
- record length of metal rod, tap with a hammer and record peak frequency displayed on computer or phone
- repeat x3 for average and use wavelength (rod length x2) to calculate speed
- record length of metal rod, tap with a hammer and record peak frequency displayed on computer or phone
- Use an oscilloscope to measure the speed of sound
- Wave behaviour at boundaries
- waves are absorbed, transmitted and reflected at boundaries
- Refraction = changing direction
- if wave hits boundary at angle it changes direction
- if wave hits boundary at normal it will continue straight on
- normal is imaginary line perpendicular to boundary
- how much a wave refracts depends on wavelength
- wavefront diagrams show refraction
- part that hits denser material first slows down, causing wave to turn
- car wheel stuck in mud or a puddle would turn
- part that hits denser material first slows down, causing wave to turn
- Investigating refraction
- uses a thin ray of light, so do experiment in a dark room
- light refracted at the boundary between air and glass
- trace incident and emergent rays by shining light from ray box
- remove the glass bock and join them up
- draw normal, measure angles and repeat 3 times to find avergae
- remove the glass bock and join them up
- EM Waves
- tranverse waves that travel at the same speed through a vaccum
- Wavelengths vary from 10^-15m to more than 10^4m
- Our eyes can only detect visible light, but there's infrared, micro waves, radio waves, ultraviolet, x-rays and gamma rays
- Different properties
- Radio waves transmitted through the body without being absorbed
- Some wavelengths of microwaves absorbed
- IR and Visible light are mostly reflected or absorbed
- Ultraviolet has a higher frequency and can cause ionising radiation - skin cancer, blindness
- X-rays and gamma rays have even higher frequencies
- EM Waves for communication
- Radio waves are made by oscillating charges
- Charges oscillate in the transmitter and the radio waves are absorbed by the reciever
- Mainly used for communication and broadcasting
- long wave radio can be recieved halfway round the world from where they started
- Short wave radio signals reflected by the atmosphere
- Bluetooth uses short wave radio waves
- EM waves pass easily through watery atmosphere to satellites
- Radio waves are made by oscillating charges
- Microwaves and Infrared
- Microwaves in ovens have a different wavelength to penetrate a few cm into food and transfer energy to water molecules to heat up
- IR cameras can detect heat sources and turn this into an electrical signal (thermal imaging)
- IR uses include police searches, security systems or alarms, heaters
- IR radiation can be used to transfer information short distances eg. tv remote, phone, laptop
- More uses of EM Waves
- Photography uses Visible Light
- Ultraviolet is used in fluorescent lamps and security pens
- X-ray photographs can be used for medical purposes
- Gamma rays can be used as cancer treatments and to sterilise medical equipment
- Wave Basics
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