Magnetism(चुम्बकत्व)-mpsc science

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Intro of Magnetism(चुम्बकत्व)

➤Magnet is an object that attracts objects made of iron, cobalt and nickle.
➤ Magnet comes to rest in North – South direction, when suspended freely.
Use of Magnets
➤Magnets are usedin refrigerators.
➤ radio and stereo speakers.
➤ audio and video cassette players.
Properties of Magnet
➤ The pole of a magnet which points toward north direction is called north pole or north-seeking..
➤ A free suspended magnet always points towards the north and south direction.
➤ The pole of a magnet which points toward south direction is called south pole or south seeking.
➤ Like poles of magnets repel each other while unlike poles of magnets attract each other.
what is Magnetic Field ?
➤ The area around a magnet where a magnetic force is experienced is called the magnetic field
➤ It is a quantity that has both direction and magnitude, (i.e., Vector quantity)
➤ The influence of force surrounding a magnet is called magnetic field.
➤In the magnetic field, the force exerted by a magnet can be detected using a compass or any other magnet.The magnetic field is represented by magnetic field lines.
➤The imaginary lines of magnetic field around a magnet are called field line or field line of magnet.
When iron fillings are allowed to settle around a bar magnet, they get arranged in a pattern which mimicks the magnetic field lines.
➤ Field line of a magnet can also be detected using a compass.
➤ Magnetic field is a vector quantity, i.e. it has both direction and magnitude
Direction of field line
➤ Outside the magnet, the direction of magnetic field line is taken from North pole to South Pole. Inside the magnet, the direction of magnetic field line is taken from South pole to North pole.

Strength of magnetic field
➤ The closeness of field lines shows the relative strength of magnetic field, i.e. closer lines show stronger magnetic field and vice – versa. Crowded field lines near the poles of magnet show more strength.
Properties of magnetic field lines
➤ They do not intersect each other.
➤ It is taken by convention that magnetic field lines emerge from North pole and merge at the South pole. Inside the magnet, their direction is from South pole to North pole. Therefore magnetic field lines are closed curves.
➤ A current carrying straight conductor has magnetic field in the form of concentric circles, around it.
➤Magnetic field of current carrying straight conductor can be shown by magnetic field lines.
➤The direction of magnetic field through a current carrying conductor depends upon the direction of flow electric current.
➤Let a current carrying conductor be suspended vertically and the electric current is flowing from south to north. In this case, the direction of magnetic field will be anticlockwise. If the current is flowing from north to south, the direction of magnetic field will be clockwise.
➤The direction of magnetic field, in relation to direction of electric current through a straight conductor can be depicted by using the Right Hand Thumb Rule. It is also known as Maxwell’s Corkscrew Rule.

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Right-Hand Thumb Rule

➤ If a current carrying conductor is held by right hand, keeping the thumb straight and if the direction of electric current is in the direction of thumb, then the direction of wrapping of other fingers will show the direction of magnetic field."

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Maxwell’s Corkscrew rule

➤As per Maxwell’s Corkscrew Rule, if the direction of forward movement of screw shows the direction of the current, then the direction of rotation of screw shows the direction of magnetic field.

Clock Face Rule

➤ A current carrying loop works like a disc magnet.
➤The polarity of this magnet can be easily understood with the help of Clock Face Rule.
➤ If the current is flowing in anti – clockwise direction, then the face of the loop shows north pole.
➤ On the other hand, if the current is flowing in clockwise direction, then the face of the loop shows south pole
Magnetic field due to a current in a Solenoid ➤ Solenoid is the coil with many circular turns of insulated copper wire wrapped closely in the shape of a cylinder.
➤A current carrying solenoid produces similar pattern of magnetic field as a bar magnet.
➤One end of solenoid behaves as the north pole and another end behaves as the south pole.

Electromagnet

➤An electromagnet consists of a long coil of insulated copper wire wrapped on a soft iron.
➤Magnet formed by producing magnetic field inside a solenoid is called electromagnet.
➤A current carrying conductor exerts a force when a magnet is placed in its vicinity
➤imilarly, a magnet also exerts equal and opposite force on the current carrying conductor
➤his was suggested by Marie Ampere, a French Physicist and considered as founder of science of electromagnetism.

Fleming’s Left-Hand Rule

➤ If the direction of electric current is perpendicular to the magnetic field, the direction of force is also perpendicular to both of them
➤ The Fleming’s Left Hand Rule states that if the left hand is stretched in a way that the index finger, the middle finger and the thumb are in mutually perpendicular directions, then the index finger and middle finger of a stretched left hand show the direction of magnetic field and direction of electric current respectively and the thumb shows the direction of motion or force acting on the conductor.
➤The directions of electric current, magnetic field and force are similar to three mutually perpendicular axes, i.e. x, y, and z-axes.
➤Many devices, such as electric motor, electric generator, loudspeaker, etc. work on Fleming’s Left Hand Rule.

Fleming's right-hand rule

➤Fleming's right-hand rule stipulates that the index finger, middle finger and right thumb are perpendicular to each other, so that the index finger points in the direction of the external magnetic field and the thumb points in the direction of the conductor.
➤Now, the direction in which the middle finger points gives the direction of the induced current in the conductor.
➤Fleming's right-hand rule is used to determine the direction of current induced in the conductor when it moves in the magnetic field.

Electric motor

➤A device that converts electrical energy to mechanical energy.
➤It is of two types : AC and DC Motor
➤Electrical energy is converted into mechanical energy by using and electric motor.
➤Electric motor works on the basis of rule suggested by Marie Ampere and Fleming’s Left Hand Rule.
Principle of Electric Motor
➤ When a rectangular coil is placed in a magnetic field and a current is passed through it, force acts on the coil, which rotates it continuously. With the rotation of the coil, the shaft attached to it also rotates.

Electromagnetic Induction

➤ Michael Faraday, an English Physicist is supposed to have studied the generation of electric current using a magnetic field and a conductor.
➤Electricity production as a result of magnetism (induced current) is called Electromagnetic Induction.

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A.C and D.C Current

A.C – Alternate Current
➤ Current in which direction is changed periodically is called Alternate Current.
➤ In India, most of the power stations generate alternate current.
➤ The direction of current changes after every 1/100 second in India, i.e. the frequency of A.C in India is 50 Hz.
➤ A.C is transmitted upto a long distance without much loss of energy is advantage of A.C over D.C.
D.C – Direct Current
➤ Current that flows in one direction only is called Direct current. Electrochemical cells produce direct current. Advantages of A.C over D.C
➤ Cost of generatior of A.C is much less than that of D.C.
➤ A.C can be easily converted to D.C.
➤ A.C can be controlled by the use of choke which involves less loss of power whereas, D.C can be controlled using resistances which involves high energy loss.
➤ AC can be transmitted over long distances without much loss of energy.

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➤AC machines are stout and durable and do not need much maintenance.
Disadvantages of AC
➤AC cannot be used for the electrolysis process or showing electromagnetism as it reverses its polarity.
➤AC is more dangerous than DC.
The 3 wires are as follows
➤ Live wire – (Red insulated, Positive)
➤ Neutral wire – (Black insulated, Negative)
➤ Earth wire – (Green insulated) for safety measure to ensure that any leakage of current to a metallic body does not give any serious shock to a user.
➤ Short Circuit: Short-circuiting is caused by the touching of live wires and neutral wire and sudden a large current flows.It happens due to damage pf insulation in power lines.
Electric Fuse
➤ It is a protective device used for protecting the circuit from short-circuiting and overloading. It is a piece of thin wire of material having a low melting point and high resistance.
➤ Fuse is always connected to live wire.
➤ Fuse is always connected in series to the electric circuit.
➤ Fuse is always connected to the beginning of an electric circuit.
➤ Fuse works on the heating effect.

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