IMPORTANT NOTES
1. Magnetic field: The space surrounding a magnet in which its influence in the form of magnetic force can be detected, is called magnetic field.
2. When an electric current is passed through a conductor, then a magnetic field is produced around the conductor, i.e., the conductor behaves like a magnet, as long as the current flows through it.
3. Ampere’s swimming rule: Imagine a swimmer, swimming in the direction of flow of current and always looking towards the needle, such that current enters from his feet and leaves from his head. The direction in which the left hand of the swimmer points, gives the direction of motion of the north pole of the magnetic needle.
4. SNOW Rule: The direction of motion of the north pole of the magnetic needle can be found out by the remembering the word SNOW, where S stands for south, N for north, O for over and W for west.
5. Right hand thumb rule: Imagine you are holding the conductor with the palm of your right hand, such that fingers encircle the conductor and the thumb points in the direction of the current. Then the direction of the fingers encircling the conductor, gives the direction of the magnetic lines of force around it.
6. Solenoid: An insulated copper wire wound on some cylindrical cardboard or plastic tube, such that its length is greater than its diameter and it behaves like a magnet when a current is made to flow through it, is called a solenoid.
7. Electromagnet: A solenoid which has an iron core within it is called electromagnet. The iron core intensifies the magnetic field of the solenoid, as iron gets magnetised due to magnetic induction.
8. Fleming’s left hand rule: Stretch the thumb, the fore finger and the middle finger of your left hand mutually at right angles to each other, such that the forefinger points in the direction of the magnetic field and the middle finger in the direction of flow of current. Then thumb gives the direction of motion of conductor.
9. Electric Motor: An electric motor is a device which converts electric energy into mechanical energy.
10. Commutator: A rotating device which changes the direction of current after every half rotation is called the commutator.
11. Fleming’s right hand rule: Stretch the palm of your right hand in such a way that the thumb, the fore finger and the middle finger are mutually at right angles to each other. Now point the thumb in the direction of motion of the conductor and fore finger in the direction of the magnetic field. Then the direction of the middle finger gives the direction of the induced current.
12. Electromagnetic Induction: The phenomenon due to which a changing magnetic field within a conductor or closed coil induces electric current in the conductor or a coil is called electromagnetic induction.
13. Induced current: The alternating current produced in a conductor or a closed coil, when the magnetic lines of force rapidly change in it, is called the induced current. Induced current is always alternating in nature.
14. Lenz’s law: It states “In all cases of electromagnetic induction, the direction of induced current is such that it always opposes the cause (the motion of the conductor) which produces it.”
15. Mutual Induction: The phenomenon of production of induced e.m.f. in a closed coil, by varying the magnetic flux in another coil is called mutual induction.
16. Alternating current: An electric current in which the direction of current changes after equal intervals of time is called alternating current (AC). The electric current supplied for domestic or industrial use is alternating current.
17. Electric generator: It is based on the phenomenon of electromagnetic induction. It converts mechanical energy to electric energy.
18. Household wiring is done in parallel. It is provided with safety devices such as fuse and earthing.
19. Electricity for domestic purposes is supplied at 220 V and 50 Hz. Commercial electricity is supplied at 440 V and 50 Hz.
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