ELECTROMAGNETISM What is Electromagnetism? Electromagnetism describes the relationship between electricity and magnetism. We use electromagnets to generate electricity, store memory on our computers, generate pictures on a television screen, diagnose illnesses, and in just about every other aspect of our lives that depends on electricity. Electromagnetism works on the principle that an electric current through a wire generates a magnetic field around that wire. If the current carrying wire is placed inside a magnetic field, the wire experiences a force on it and moves perpendicularly to the magnetic field. This is also known as the motor effect. The direction of the force can be found by using Fleming’s Left Hand rule.
If the direction of current is reversed, the direction of the force is also reversed. NOTE: To find the direction of force on a beam of electrons, use the same rule but reverse the direction of the force. This is because the direction of flow of electrons is opposite to the direction of current. A cross (x) means that the magnetic field is into the page. A dot (.) means that the magnetic field is out of the page.
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The direction of the force is upward in case of the current but downward in the opposite direction in the case of an electron beam.
USE OF ELECTROMAGNETISM: 1. DC MOTOR
commutator direction of magnetic field
2. MOVING COIL LOUDSPEAKER
When current moves in the coil of wire inside the magnetic field, it experiences a force moving the paper cone outward. When the direction of the current changes (ac) the direction of the force also changes pulling the cone inward. The constant change of force causes the cone to vibrate and produce sound in the surrounding air.
3. GALVANOMETER: it is a device used to measure sensitive currents. It uses the motor effect to turn the pointer around when a current passes through the coil. When the current is switched off, the spring brings the pointer back to zero.
TO INCREASE THE TURNING EFFECT OF THE COIL IN A MOTOR: 1. 2. 3. 4. 5.
INCREASE THE CURRENT IN THE COIL USE STRONGER MAGNETS INCREASE THE NUMBER OF TURNS ON THE COIL INCREASE THE NUMBER OF COILS USE A SOFT IRON CORE
By Shafaq Hafeez shafaq@physics.com.pk