Credit cardMagnetic strip contains iron-based domains that can be aligned by a magnetic eldEach magnetic particle in the stripe is a tiny bar magnet about 20-millionths of an inch longTo encode information on to the magnetic strip, the domains can be polarised in either north or south, representing a two-state system much like binaryThis process is called ux reversalMagnetic elds:!Flemings left hand rule!F = BIL!When a current ows through a wire a magnetic eld is produced around the wireCard readerThe magnetic stripe reader reads the information by detecting the changes in the magnetic eld caused by the ux reversals on the cards magnetic stripeScreen generated by photons of light!Light is refracted as it changes medium from air to plastic screen back into air againSpring system in the buttons obeying Hookes law: F=keOn a table - obeying Newtons Third Law. Card reader exerts forces on table so table exerts equal and opposite (in direction) force on the card readerQuestion