L3 Physical Science Electromagnetic Induction

Lecturer: Semase M.P Physical Science L3 Downloaded Sefikeng Campusfrom hlayiso.com

Subject outcome State, analyse and apply principles of electromagnetism Learning outcomes • Identify and draw diagrams of the magnetic field associated with a current. • Long straight current carrying conductor and in a solenoid. • Identify and describe the use of magnetic field and its application in electromagnets. • Identify the effect of the magnetic field on a charged particle in motion. • Describe and apply electromagnetic induction to produce current by changing magnetic field and how it is applied in dynamos and transformers. Downloaded from hlayiso.com

INTRODUCTION How magnetic field affect conductors • Michael Faraday discovered that if you move a conductor through a magnetic field an electric current will flow through the conductor. This phenomena is known as electromagnetic induction. • When you push the magnet into the solenoid, the galvanometer needle deflects in one direction. When the magnet is stationery, there should be no deflection on the galvanometer • If the poles of the magnet are reversed, all the deflection happen in the opposite direction. Downloaded from hlayiso.com

Dynamos • A dynamo transforms mechanical energy into electrical energy. • The dynamo consists of a large number of coils of wire wound around an armature that rotates in a magnetic field • The axle is driven by some mechanical means such as water or steam • When the arm of the coil moves upward, current is induced in one direction and when it moves downwards current is induced in the opposite direction Downloaded from hlayiso.com Figure 1: Dynamo

Transformers • A transformer is another device that depends on elctromagnetic induction • In the transformer, an alternating current flows in one coil and the changing magnetic field around this coil induces a current in another vicinity • The coil connected to the input voltage is called the primary coil • The output coil is called the secondary coil • A transformer with mire turns on the primary than the secondary is called a step down transformer • A transformer with fewer turns on the primary than on the secondary is called a Figure : transformer step up transformer Downloaded from hlayiso.com

Summary • Electromagnetic induction means causing a current to flow in a conductor by moving it through a magnetic field. • Electromagnetic induction occurs only when there is relative motion of the conductor and the magnetic field. • A dynamo is a device that is used to generate electricity. • Transformers are used to step up or step down voltage. • A transformer has primary and secondary coil. Downloaded from hlayiso.com

Assessment activity • What is electromagnetic induction (2) • Name three factors on which the size of the current induced in a solenoid by a magnet depends (6) • Explain how generator works (5) • Explain in detail how a transformer works (7) Downloaded from hlayiso.com