Flashcards in Waves Deck (53):
What do waves do?
Transfer energy in the direction they are travelling
When waves travel through a medium the particles of the medium oscillate and transfer energy between each other but the particles stay in the same place. Only energy is transfered
Waves have 3 things. What are they?
Amplitude- maximum displacement of a point on a wave from its undisturbed position
Wavelength- distance between the same point on two adjacent waves
Frequency- number of waves passing a certain point per second
(See annotated diagram on page 105 of revision guide for more)
What is the formula for frequency of a wave?
Period (T) = 1/ frequency (f)
Frequency measured in hertz Hz
Period measured in seconds s
What kinds of vibrations do transverse waves have?
Transverse waves have perpendicular vibrations to the direction of energy transfer.
What waves are transverse?
All waves on the electromagnetic spectrum
Ripples and waves in water
A wave on a string
What kind of vibrations do longitudinal waves have?
Oscillations are parallel to the direction of energy transferred
What are examples of longitudinal waves?
Sound waves in air, ultra sound
Shockwaves eg some seismic waves
What is the wave speed equation?
Wave speed (m/s) = frequency (Hz) x wavelength (m)
v=f x (that landa sign thingy)
What is wave speed?
The speed at which energy is being transferred.
How to use an oscilloscope to measure the speed of sound and speed of water ripples?
See page 107 of revision guide
(Don’t think we have covered this)
How to find wave speed of wave on a spring?
Set up signal generator, vibration transducer, string, pulley and mass (as shown on of 108 of revision guide).
Turn on signal generator and vibration transducer. The string will start to vibrate
You can adjust frequency to change wave length . Adjust until there’s a clear wave (happens when whole number of half waves fit on a string), depends on length of string and masses
Measure wavelength using ruler
Frequency of wave is whatever signal generator is set too
Use wave length equation to find wave speed
(For more clarity see 108 in revision guide)
What is refraction?
When light waves are bent when they enter a new media
When wave arrives at a boundary between 2 different materials, what are the 3 things that can happen?
Wave is ABSORBED by second material- transfers energy to materials energy store. This often leads to heating. Can be used in microwaves
Wave is TRANSMITTED through the second material- waves carry on travelling through the new material. This often leads the refraction. Used in glasses lenses and cameras and communication
Wave is REFLECTED- it’s sent back away from second material
Which of these happens depends on wavelength and properties of materials
When a wave crosses a boundary between 2 materials it changes speed
If a wave is travelling along the normal it will change speed but not refracted, If hit at an angle is changes direction and is refracted
Waves bends towards normal if it slows down and away from it if it speeds up- how much it’s refracted depends on change in speed which depends on density of material, higher density slower wave
When a wave is refracted what changes and what stays the same?
Wave length changes but frequency stays the same
What is optical density?
A measure of how quickly light can travel through it, higher optical density, slower light travels through it
How do you construct a ray diagram to show refraction?
Draw boundary between two materials
Draw normal line perpendicular to boundary
Draw incident ray that meets normal at the boundary. Angle between ray and normal is angle of incidence
Draw refracted ray in other side. Angles between refracted ray and normal is small than angle of incidence unless second material is less optically dense.
What type of waves are those on the electromagnetic spectrum?
Transverse waves that’s transfer energy from a source to an absorber
What speed do different EM waves travel at?
All Em waves travel at the same speed through air or a vacuum
Finish the blanks. Electromagnetic waves form a _________ over a range of ___________. They are grouped into 7 basic types based on their ______ and _________
What are the 7 wave types on the EM spectrum?
Infra red radiation
What part of the EM spectrum can our eyes detect?
Why is their such a large range of frequencies in the EM spectrum?
Because EM waves are generated by a variety of changes in atoms and their nuclei.
This also explains why atoms can absorb a range of frequencies- each one causes a different change
Why are EM waves used for different purposes?
They have different properties
How are radio waves made?
By oscillating charges
EM waves are made up of electric and magnetic fields AC made up of oscillating charges, as charges oscillate they produce oscillating electric and magnetic fields
Frequency of waves produced is equal to frequency of alternating current.
How can you produce radio waves?
Using alternating current in an electrical circuit
What is a transmitter?
An object in which charges oscillate to create radio waves.
What happens when transmitted radio waves reach a receiver?
Radio waves are absorbed . The energy transferred by the wave sis transferred to the electrons in the material of the receiver. This energy causes electrons to oscillate and if the receiver is part of compete electrical circuit it generates alternating current. This current has the same frequency as the radio waves that generated it.
What are radio waves?
EM radiation with wavelengths longer than about 10cm
What are the uses of radio waves?
Long wave radio waves (wavelength 1-10km) used for radio signals as can diffract around hills etc
Short wave radio signals (10-100m) used for Bluetooth, tv and fm radio
What the uses of microwaves?
Satellites use them
Microwaves use them
Satellite tv- signs from transmitter transmitted into space where it’s picked up by satellite receiver dish transmitting signal back to earth in different directions where it’s received by a satellite dish in the ground
Uses of infrared radiation?
Used to monitor temperature or increase it (absorbing IR causes objects to get hotter)
Uses of ultraviolet radiation?
Security pens- allows you to read invisible ink
Uses of visible light
Fibre optic cables use it to transmit data
These work via reflection, light rays are bounced back and fourth until they reach the end in the fibre
Uses of X-rays
Uses of gamma rays
Used to treat cancer
Which EM radiation can be harmful to people?
High frequency waves like UV rays , X rays and gamma rays transfer lots of energy so can cause lots of damage.
What is radiation dose?
The Measure of the risk of harm form the body being exposed to radiation.
Risk depends on how much is absorbed and how harmful that radiation is.
It is measure in sieverts but a sievert is very big so often see doses in millisieverts where 1000mSv = 1 Sv
Risk can also vary dependent in different parts of the body
What does every object absorb and emit
Hotter object= more infrared radiation emitted over time. If obejects is hotter than surrounding it emits more than absorbs and cools down
Black matte surface is best at absorbing and emitting radiation
What do magnets produce?
Why are the two poles of a magnet?
North and south
How can you show and magnetic field?
By drawing field lines
Closer together like the stronger the magnetic field is
Means magnetic forces are strongest at poles
What’s is force between magnet and magnetic material?
It is always attractive no matter the poles
What happens if toe poles if a magnet are put near each other.
Is they are the same they repel
How does a compass work?
Inside compass is tiny bar magnet (needle)
North Pole of magnet is attracted to south pole of any other magnet it is near, do compass needle points in direction of magnetic field it is in . When not near a magnet compass needles point north as earth has its own magnetic field, showing earths core is magnetic
What are the two types of magnet?
Permanent- produce their own magnetic field
Induced- magnetic materials that are turned into magnet when put into a magnetic field, take ways magnetic field and lose most of magnetism
Force between permanent and induced magnet is always attractive
What creates a magnetic field?
A moving charge -
When a current flows through a wire a magnetic field is created around the wire. Changing direction of current changes direction of magnetic field , strength of magnetic field changes with current and distance from wire, larger current and closer to wire means stronger field
What’s an electromagnet?
A magnet that can me switched on and off
How do you increase strength of a magnetic field?
Wrapping the wire in a coil called a solenoid
Happens as field lines around each wire line up very close to each other, meaning stronger field
Magnetic field inside solenoid is strong and uniform, outside coil is just the same as the one around a bar magnet
Can increase field strength even more by putting iron in centre, becomes induced magnet when current is flowing
What does a current in a magnetic field experience?
What is the motor effect?
When current carrying wire is put between magnetic poles magnetic field around the wire interacts with the magnetic field it has been placed in. Causes magnet and conductor to exert a force on each other , this can cause the wire to move
To experience full force wire has to be 90 degrees to magnetic field. If wire runs parallel to magnetic field it won’t experience any force at all, at angles between if will experience some
What does the force acting on the conductor in a magnetic field depend on?
Magnetic flux density- how many field lines in a region
Size of current through a conductor
Length of conductor that in the magnetic field