Cie igcse 0625 physics revision 2017 and 2018

A.C generator In  direct current  ( DC ), the electric charge ( current ) only flows in one direction. Electric charge in alternating  current  ( AC ), on the other hand, changes direction periodically. The voltage in  AC  circuits also periodically reverses because the  current  changes direction. • The coil is made of insulated copper wire and is rotated by turning the shaft. The slip rings are fixed to the coil and rotate with it. The brushes are 2 contacts which rub against the slip rings and keep the coil connected to the outside part of the circuit, usually made of carbon. When the coil is rotated, it cuts magnetic field lines, so an EMF is generated, which makes a current flow. Each side of the coil travels upwards then downwards then upwards etc. so the current flows backwards then forwards then backwards etc. so it is an alternating current. The current is maximum when the coil is horizontal since field ...

The magnetic effect of a current  Magnetic field around a current carrying wire and a solenoid:

D.C motor When a current-carrying coil is in a magnetic field, it experiences a turning effect. A DC motor runs on a direct current. The coil is made of insulated copper wire. It is free to rotate between the poles of the magnet. The commutator , or split-ring, is fixed to the coil and rotates with it. When the coil overshoots the vertical, the commutator changes the direction of the current through it, so the forces change direction and keep the coil turning. The brushes are two contacts which rub against the commutator and keep the coil connected to the battery. They are usually made of carbon. The maximum turning effect if when the coil is horizontal. There is no force when the coil is vertical (but luckily it always overshoots this position). The turning effect can be increased by: -increasing the current -using a stronger magnet -increasing the number of coils (increases the length of coil) -increasing the area of th...

The nuclear atom Atomic model 

Detection of radioactivity  Background radiation : the small amount of radiation around us all the time because of radioactive materials in the environment. It mainly comes from natural sources such as soil, rocks, air, building materials, food and drink – and even space. • Detection: Alpha particles – the cloud chamber : A chamber has cold alcohol vapour inside it. The alpha particles make the vapour condense, so you see a trail of tiny droplets. It is useful because it makes the tracks visible. Alpha, Beta and Gamma – the Geiger-Müller (GM) tube The “window” end is thin enough for alpha particl es to pass through. If an alpha particle enters the tube, it ionizes the gas inside. This sets off a high-voltage spark across the gas and a pulse of current in the circuit. A beta particle or gamma radiation has the same effect. It can be connected to a ratemeter (tells the counts per seconds), a scaler (tells the total num...