1. USING ELECTRICITY – Class 7 MAGNETIC EFFECTS OF ELECTRICITY Done by Mrs. Aparna.S

2. MAGNETIC EFFECT OF ELECTRICITY Concept, Application and Uses

3.  Hans Christian Oersted: In 1820, during a classroom demonstration of an experiment to his students, he noticed that a compass needle was deflected when an electric current was switched on nearby. He went on to study this effect further and discovered the connection between electricity & magnetism. MAGNETIC EFFECT OF ELECTRICITY

4. MAGNETIC EFFECT OF ELECTRICITY – Oersted’s experiment

5.  A compass needle can only be deflected by a magnet  When a current passes through a wire, it behaves like a magnet and has a magnetic effect around it  The area around it where the magnetic influence is felt is called the magnetic field caused due to electricity MAGNETIC EFFECT OF ELECTRICITY – Oersted’s experiment and explanation

6.  Thus, a coil of wire acts as a magnet when current flows through it  A solenoid is a cylindrical coil of wire that behaves like a bar magnet, with opposite poles at the ends, when a current flows in it MAGNETIC EFFECT OF ELECTRICITY - Solenoid

7.  Thus, a coil of wire acts as a magnet when current flows through it  If the coil is wound around a soft iron core such as an iron nail, the magnetic effect increases several times  An electromagnet is a coil wound around an iron core which acts as a magnet as long as an electric current flows through the coil MAGNETIC EFFECT OF ELECTRICITY - Electromagnet

8. Useful properties of electromagnets: 1. Increase in current increases the strength of the electromagnet 2. They are very strong temporary electromagnets and become demagnetised as soon as the current is switched off 3. They come in varying shapes and sizes depending on their purpose MAGNETIC EFFECT OF ELECTRICITY - Electromagnet

9. Application: 1. Used to make electric motors that are used in fans, refrigerators, AC units, electric bells, telegraph, telephones, loudspeakers, washing M/C s 2. Used to separate iron and steel from other materials in a metal scrapyard 3. Used in magnetic cranes for lifting and carrying heavy steel and cast iron articles in factories MAGNETIC EFFECT OF ELECTRICITY - Electromagnet

10. The electric bell is a simple device that uses an electromagnet. It is used as a doorbell. An electric bell consists of a battery, an electric switch, an electromagnet, an adjusting screw, a soft iron strip, a hammer and a gong. MAGNETIC EFFECT OF ELECTRICITY – The Electric Bell

11. How it works? 1. When you push the switch of a bell, the electric current flows to the electromagnet. 2. The electromagnet attracts the soft iron strip. The hammer attached to the strip then hits the gong, causing a ring. 3. This movement breaks the circuit at the contact screw so that the current stops flowing and switches off the electromagnet. MAGNETIC EFFECT OF ELECTRICITY – The Electric Bell

12. How it works? 4. The metal strip pulls back next so that contact is made again at the contact screw and the circuit is complete and current flows again. Steps 1-4 keep repeating as long as the switch is on. 5. Thus, the hammer repeatedly strikes the gong producing a continuous ringing sound as long as the switch is pressed.