"AKC SCIENCE CLASSES"
CLASS 10 TH (CBSE AND MP BOARD)
CHAPTER 13
MAGNETIC EFFECTS OF ELECTRIC CURRENT
BASIC CONCETS
1) Magnetic and Magnetism :- The substances which have the property of attracting small pieces of iron, nickel, cobalt etc., are called magnets and this property of attribution is called magnetism.
2) Natural magnet :- It is a piece of lodestone, which is a black iron oxide (Fe₃O₄) called magnetite. The word lodestone means a leading stone.
3) Magnetic poles :- The regions of concentrated magnetic strength inside the magnet just near its ends are called magnetic poles. The pole of a freely suspend magnet which points towards north is called north pole and that points towards south, is called south pole.
4) Law of magnetic poles :- It states that like poles repel while unlike poles of magnets attract each other.
5) Basic properties of magnets :-
- Magnets attract small pieces of iron, nickel, cobalt, etc.
- When freely suspended, they come to rest in north-south direction.
- Like magnetic poles repel each other and unlike magnetic poles attract each other.
- The magnetic poles always exist in pairs.
6) Artificial magnets :- Pieces of iron and other magnetic materials which can be made to acquire the properties of natural magnets are called artificial magnets.
7) Magnetic fields :- It is the region around a magnet within which its influence can be experienced.
8) Magnetic line of force :- It may be defined as the path in a magnetic field in which a unit north pole tends to move when allowed to do so. It may also be defined as a curve, the tangent to which at any point gives the direction of the magnetic field at that point.
9) Compass needle :- It is a small magnetic needle pivoted at the center of a small circular brass case provided with a glass top. It is used to find the direction of magnetic field.
10) Magnetic effect of current :- A current carrying conductor is always associated with a magnetic field around it. This is called the 'magnetic effect of current'. It was first discovered by Haris Christian Oersted in 1820.
11) Magnetic field around a straight current carrying conductor :- The magnetic field consists of concentric circular lines of force around the conductor. The direction of the field i determined by using the following rules :-
- Right hand thumb rule :- If the current carrying conductor is held in the right hand such that the thumb points in the direction of the current, then the direction of the curl of the fingers will give the direction of the magnetic field.
- Maxwell's corkscrew rule :- If a right handed screw be rotated along the wire so that it advances in the direction of current, then the direction in which the screw rotates gives the direction of the magnetic field.
13) Magnetic field of a circular current carrying coil :- Near the circumference of the wire, the magnetic lines of force are in the form of concentric circles. Near the center of the loop, the lines of force are almost straight and parallel. Hence, near the center, the magnetic field is uniform and normal to the plane of the loop.
14) Solenoid :- A long cylindrical coil of insulated copper wire of large number of circular turns is called a solenoid. A current carrying solenoid behaves like a bar magnet. Polarity of its any end can be determined by using clock rule by noting the direction of the direction of the flow of current. If the current is anticlockwise, the end is a north pole and if the current is clockwise, the end is a south pole.
15) Electromagnet :- It is a solenoid with a soft iron core placed inside it. When current is passed through the solenoid, the soft iron core becomes a temporary magnet. The strength of an electromagnet can be increased by
- increasing the number of turns per unit length of the coil,
- increasing the strength of current, and
- winding the coil over a soft iron core.
16) Force on a current carrying conductor placed in a magnetic field :- In 1820, Ampere demonstrated that a current carrying conductor placed in a magnetic field experiences a force. If the direction of the field and that of the current are mutually perpendicular to each other, then the force acting on the conductor will be perpendicular to both and is given by Fleming's left hand rule.
17) Fleming's left-hand rule :- This rule gives the direction of the force exerted on a current carrying conductor placed in as magnetic field. According to this rule if we hold the thumb, the forefinger and the central finger of the left-hand mutually perpendicular to each other and if the forefinger points in the direction of the magnetic field, central finger in the direction of the current, then the thumb points in the direction of motion (or the force) on the conductor.
18) Factors on which the force experienced by a current carrying conductor placed in a magnetic field depends :- The force F exerted on a conductor of length L, carrying current I and placed perpendicular to a magnetic field B is given by
F = BIL
No force is exerted on a stationary charged particle in a magnetic field.
19) SI unit of magnetic field is tesla (T) :- One tesla is that magnetic field in which a charge of a one coulomb moving with a velocity of 1m/s perpendicular to the magnetic field experiences a force of one newton.
20) Electric motor :- It is a device to convert electrical energy into mechanical energy. It is based on the principle that when a current carrying coil is placed in a magnetic field, it experiences a torque. Our daily appliances such as electric fans, washing machines, mixers and blenders use electric motors.
21) Electromagnetic induction :- Whenever the magnetic lines of force passing through a closed circuit change, a voltage and hence a current is induced in it. This phenomenon is called electromagnetic induction. It was discovered by Michael Faraday in 1831.
22) Fleming's right-hand rule :- This rule gives the direction of induced current in a conductor. According to this rule if we hold the thumb, the forefinger and the central finger of right-hand mutually perpendicular to each other and if the forefinger points in the direction of the magnetic field, the thumb in the direction of motion of the conductor, then the central finger points in the direction of the induced current in the conductor.
23) Electric generator or a dynamo :- It is a device to convert mechanical energy into electrical energy. It is based on the principle of electromagnetic induction that a current is induced in a field passing through it changes.
24) Direct current :- It is that current which flows in a circuit with a constant magnitude in the same direction.
25) Alternating current :- It is that current whose magnitude and direction change alternately and regularly with the passage of time.
26) Domestic wiring :- The electricity from tha mains is supplied to the houses using a three-core wiring called the 'live', the neutral and the earth. The live wire is red in color and brings in the current. The black neutral wire is the return wire. The green earth wire is connected to a metal plate deep in the earth. It is a safety measure and does not affect the supply in any way.
27) Electric fuse :- It is a safety device to protect an electric circuit from overloading or short circuiting. It is a piece of wire of a material of low melting point which is connected to the live wire in the circuit. When an excessive current flows, the fuse melts and the circuit is broken. Fuse wire is made of pure tin or tin-copper alloy.
28) Earthing :- Earthing of an electrical appliance means connecting the metallic body of the powered appliance to the earth through the earth wire. It is a safety measure which ensures any leakage of current to the metallic body of the appliance keeps its potential equal to that of the earth (zero volt) and the user may not get a severe electric shock.
29) Overloading :- If the current drawn from the mains exceeds the safety limit (5A for domestic line and 15 A power line), then this is known as overloading. A circuit can be protected from overloading by using an electric fuse.
30) Short circuiting :- If due to defective or damage wiring, the live and neutral wires come in direct contact, the resistance of the circuit becomes almost zero and an extremely large current flows through the circuit. This is called short circuiting. Appliances can be protected from short circuiting by using an electric fuse in live wire.
