CBSE Mgnetic Effect and Electric Subject Notes

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Mgnetic Effect and Electric

Mgnetic Effect and Electric

Overloading When too many electrical appliances of high power rating (electric oven, air conditioner, etc.) are switched on at the same time, a large current from the circuit is drawn. This is called overloading of the circuit. It may also occur when the live wire and the neutral wire come into direct contact.

Steps to avoid overloading

Short circuiting When the live wire and neutral wire come into direct contact, a large amount of current flows through the circuit due to very small resistance, this is called short circuiting. The heat produced during short circuiting is so high that it may cause fire.

1. All the electric appliances should not be used at the same time.
2. Fuse wire of suitable value should be used.
3. High power rating appliances should be used with 15 A fuses.

Important Points

• Hans Christian Oersted showed the relation between electricity and magnetism. He showed that the current carrying conductor produces magnetic field around it
• Magnetic field is a vector quantity because it has both - the direction and magnitude. The direction of a magnetic field is taken to be the direction in which the north pole of a compass moves.
• The relative strength of a magnetic fields is shown be the degree of closeness of field lines. The field is stronger where the field lines are crowded.
• Straight parallel field lines inside the solenoid represent that the magnetic field is uniform inside the solenoid.
• Current carrying conductors and the magnetic fields are used in electric motors, loud speakers, microscopes, generators, measuring instruments, etc.
• There are two separate circuits in the house – the lighting circuit with 5 ampere fuse and a power circuit with a 15 ampere fuse.
• A long coil containing a large number of close turns of insulated copper wire wrapped closely in shape of a cylinder is called solenoid.
• Soft iron core is used in electromagnets because it loses its magnetism easily after stoppage of current.
• Magnetic field strength increases on increasing number of turns in the solenoid because the current in each circular turn has the same direction and the field due to each turn just adds up.
• A cable has three separate insulated wires - red, black and green. The Red insulated wire is called the live wire or positive wire. The Black insulated wire is called the neutral wire or negative wire. The Green insulated wire is called the earth wire.
• The potential difference between live wire and neutral wire is 220 volt.
• At the centre of the magnet the magnetism is zero.
• The magnetic field produced due to a circular wire at its centre is perpendicular to the plane of the wire.
• A DC generator is based on the principle of electromagnetic induction.
• An electric motor converts electrical energy into mechanical energy.
• The electric generator converts mechanical energy into electrical energy.
• Clock rule is used to find the polarities of a current carrying coil or a solenoid.
• Permanent magnets are made of alloys - steel, ALNICO (Al, Ni, Fe, Co) and Nipermag (Fe, Ni, Al, Ti).
• Soft iron is not used for making permanent magnets because it loses its magnetism easily.
• The direction and magnitude of AC change periodically while in case of DC it remains same
• Fuse wire is made up of an alloy (solder) of lead and tin because it has low melting point.
• The earth wire pin of a plug is thicker and longer than the other so that it gets connected to the earth terminal earlier than live or neutral pins and provides larger surface area. Also, it is thicker so that it may not enter the live or neutral hole of the socket.
• A compass needle placed near a current carrying wire gets deflected showing the magnetic field around it.
• The earth wire is connected to a metallic plate deep inside the earth to provide a low-resistance conducting path for current and keeps the body of appliance at the same potential as that of the earth. It is used as a safety measure so that any leakage of current to a metallic body does not give any severe shock to the user.
• The instrument that detects the presence of current in the circuit is called galvanometer.
• In India, the frequency of AC is 50 Hz i.e. it changes its direction every 1/100 second.
• The important advantage of AC over DC is that Alternating Current can be transmitted over long distances without much loss of energy.
• When a rectangular coil of copper wire is rotated in a magnetic field, the direction of the induced current changes once in each half revolution.
• A current carrying conductor placed in a magnetic field experiences a force only when the direction of current is perpendicular to the magnetic field.