Electromagnetism Flashcards
Radio waves wavelength
1m
Microwaves wav length
1cm
Infared wavelength range
1mm
Visable wavelength range
500nm
Uv wavelength range
100nm
X-rays wavelength range
10nm
Gamma rays wavelength range
Less than 1nm
Radio waves frequency range
3-10Hz^9
Microwaves frequency range
1-300Hz ^9
Infared frequency range
3-4000Hz^11
Visablelight frequency range
4-8Hz^14
Uv frequency range
8-30Hz^16
X-rays frequency
3-3000hz^16
Gamma ray frequency
10^19Hz
Radio waves source
- natural sources-lighting, astronomical phenomena
- artificial sources- broadcast radio towers, sattelite,radar, cell phones
- can be produced by oscillations in electrical circuits when aborbed by a conductor creates ac- has same frquency as radio waves
Uses of radio waves
-telecommunications
Dangers of radio waves
- very high rf intensity- heating and burns of biological tissue
- large does can cause cancer
Microwaves source
-produced inside microwave oven by an electron tube called a magnetron- microwaves are reflected within the oven
Uses of microwaves
- food
- telecommunications - short range
Dangers of microwaves
Burning
Infared radiation sources
-emmitted from heated surfaces
Uses of infared
-heating- toaster
Danegrs of infared
Burns
Visable light source
- the sun
- light bulbs
Uses of visable light
- vision- eye sight
- photography
Dangers of visable light
-blindness if intense in direct source
Uv source
Sun light
Uses uv
Sterilisation
Uv dangrs
Ionising- cancer
X-rays sources
- natural sources- radioactive elements, cosmic rays
- man made- accelerating eletrons through a pd, directing onto target material, electrons release x-rays as slow down in target
X-rays uses
Diagnosis
X-rays dangers
Ionising- cancer
Gamma rays sources
- relased during nuclear fission or radioactive decay
- eg. Nucleur explosions, lightnig, black holes, neutron stars
Gamma rays uses
Radiotherapy
Gamma rays dangers
Ionising- cancer
Magnetic north pole
North seeking pole, region at end of magnet were external magnetic field is strongest
Magnetic field lines
- shows direction felt by N pole
- more dense lines, stronger the force
Current around wire
- right thumb rile
- electric current generates magnetic field
- strength proportional to current
- concentric circles around wire
- field is weaker (less dense) further away from wire
Force on charged particles
- any moving charge produces a magnetic field around it
- in magnetic field- electron passes through uniform magnetic field
- feels force due to interacting fields(lhr)
- cause perpendicular force-circular motion
current direction
Flow of positive charge
Syncotron
- aim electrons pass around large circular building
- uses magnets to bend in certain directions
Mass spectrometer
- find mass of atom
- ionise atom
- propel by passing through magnetic field towards detector
- if accelerate less, larger mass- position on detector determines mass
Solenoid
- coil of wire
- can have holloe or iron/steel core
- current flowing through wire, produces uniform magnetic field through it
Factors which affect strength of solenoid
- no. Turns- more, stronger
- current flowing through it
- shape electromagnet
- presence iron core- increases strength
Motor effect
- two magnetic fields interacting to create force of repulsion
- current carrying wire produces a magntic field, placed inside external magnetic field (two permenant magnets) experiencing a force
Dc motor
- split ring commutator
- current in wire produces magnetic field, interacts w/ uniform field
- causing force LHR- coil rotates
- when coil parallel magnets
- no current flows, still spins due to momentum
- when passes other pole of magnet, reverse current -force felt same direction
Factors affecting motor speed
- higher current- faster rotation
- stronger electromagnetic force
- stronger uniform field, faster rotaion
- more interaction
- more turns-faster rotation
- strongr magnetic force, more field lines cut
Electromagnetic induction
- wire moved through magnetic field produces an emf
- if wire forms a circuit-current is produced
Generator effect
Right hand rule
Lenz law
Induced current flows so as to oppose th motion that made it
Faradays law
EMF enduced proportionally to rate that field lines are cut
Ac generator
- slip ring commutator
- as coil rotates, each side of coil passes diff side magnetic pole
- coil spin magnetic field, current induced
- induced current changes direction- ac
When coil parallel to magnetic field- ac generator
-large current/emf
When coil perpendicular to magnet- ac generator
-no current
Ac electrons
-vibrating back and forth
Voltage mains pd
230V
Frequency mains
50Hz
Ways to increase voltage produced- ac
- turn coil more rapidly
- use coil w/more turns
- coil bigger are
- use stronger magnets
