Chap 6 - magnetism & electricity Flashcards
properties of magnets
-always strongest at its poles (closer the magnetic lines, stronger the attraction)
-points to North when freely suspended
-attracts magnetic materials by inducing them
note:
temp. temporary
per - permanent
mag - magnet
properties of magnetic field
-lines never cross
-N to S
-closer the lines, stronger the attraction
-Cross North Close, CNC
law of magnetism
-like poles repel
-unlike poles attract
define magnetic field
-a region where a magnetic pole experiences a force
-density of lines = strength of mag
-magnetic lines loop through mag
-need arrows from N to S when drawing
define magnetic material
-materials that can be magnetized
eg. iron, cobalt, nickel
define non- magnetic material
-materials that cannot be magnetized
eg. aluminum, copper, lead, brass, tin
properties of temp mag
-made of soft iron
-loses magnetism unless near a per mag
-dont retain magnetism for a long time
-eg. electromag
properties of a per mag
-made of ferromagnetic material eg. steel, iron, nickel
-retains magnetism
-poles dont change
define electromag
-soft iron turning into a magnet when an electrical current passes through the wire
-direction is current changes poles
-a temporary magnet
-magnetic field can be controlled by turning current on & off
ferrous metals
iron, steel, cobalt, nickel
ferrous magnets
hard - steel, alloys
soft - iron, mumetal
how does electromag work
-current flows through wire & creates a magnetic field
-winding wires in a coil makes magnetic field concentrated & amplifies magnetic field strength so soft iron is magnetized
-temp mag
-mag field: in circles, strongest close to wire, more current = more mag field
-right hand grip rule:
-(wire) thumb = current direction, finger = filed lines
-(solenoid) thumb = N pole
how to increase magnetic field strength in an electromag
-more no. coils
-more current
-use a material with high magnetic permeability
how to demagnetize a mag (temp/ permanent)
-heating
-dropping magnet frequently
-hammering
-alternating direction current
(domains are forced out of alignment)
define magnetic induction
-when a magnetic material is magnetized by the presence of a per mag near it
-the side of material near the magnet is opposite the pole of the per mag
-loses magnetism when per mag is gone
-steel becomes a per. mag, iron becomes a temp. mag
-eg (per)SN SN(mag. material)
what are mag keepers made of & why
-soft iron because it’s highly magnetic
-keepers complete mag circuit to preserving per mag strength - avoid self demagnetization
note: needles in compass are inverted
-S on needles shows N pole of earth
differences btw electromag & per mag
electro:
-made of soft iron
-loses magnetism
-magnetic field can be turned on & off
-poles change depending on current direction
-magnetic field can change
per:
-made of steel
-retains magnetism
-magnetic field cannot be turned off
-fixed poles
-constant magnetic field
ways to magnetize
-induced magnetism (temp.) - temp
-using current (temp.) - temp & per depending on material
-stroking - temp & per depending on material
how does stroking work
-stroke a per. mag to a magnetic material
-pole at end of magnetic material is opp. pole of per mag
diff btw steel & iron
steel:
-hard to magnetize
-retains magnetism for long time
iron:
-easy to magnetize
-retains magnetism for short time
drawing of mag. filed
-like poles: 1 neutral middle point, magnetic fields cancel
-unlike pole: no neutral points, magnetic fields combine
how do magnets work
-electrons spin & orbit nucleus, causing a magnetic effect
-usually the effect cancels but some don’t
-unmagnetized material, electrons/ atomic mag point in random directions
-magnetized material, atomic mag align
how to show magnetic field
-drop iron fillings
-use compass & follow the needle
uses of permanent magnets
-needles of compasses
-fridge door seal
-loudspeaker
uses of electromagnets
-circuit breaker
-relay
-electric bell
uses of temp magnets
-generators
-circuit breaker
define static electricity
-build up of charged particles in 1 place which causes a small shock when discharged
-results from transfer of only electrons by friction
define current
-flow of charges
-driven by a pd
-measures in amperes (A)
relationship btw current & charge
more current, more charge
relationship btw charges
-like charges repel
-unlike charges attract
note: pd = potential difference
difference btw static & current
static - build up of charges in place
current - flow of charges
eg of insulating materials & how to charge them
eg. polythene, perspex
-rubbing it with a dry woolen cloth
-neutral materials gain opp. charge of the charged material
-electrons are transferred = imbalance in charge
-charge is localized (no free electrons to move freely)
relationship btw charge & distance
-closer the charges, the greater the distance btw them
what moves in a current
-electrons only ( - )
uses of static electricity
1)electrostatic smoke precipitators detectors:
-as the smoke particles rise up, they’re attracted to the charges plates on the side of the chimney
2)Spray painting:
-nozzle is connected to + terminal = drops are ( + )
-drop repel each other & spread out evenly
-car is connected to earth (- )
- + drops are attracted to - car
3)photocopiers:
-use static to attract black tonner to paper
is water an electrical conductor
-depends on salinity (minerals containing)
define electricity
flow of electrons around a circuit.
what is needed of electric current to flow
delocalized electrons to move
define conductoers
-material that allows charge to pass through
-has delocalized electron to carry charge
eg. copper, carbon
define insulator
-material that don’t allows charge to pass through
-no delocalized electron to carry charge
-but electrons can be transferred by static electricity/ friction
eg. plastic, glass
what is PVC
-Poly Vinyl Chloride
-insulator around wires