Magnetic field and field lines:
- Magnetic field is the region surrounding a magnet in which the force of that magnet is effective or get detected.
- Magnetic field is the vector quantity which has both magnitude as well as direction.
- The path along which magnetic field travels is called as magnetic field lines.
- Magnetic field lines start from north pole and ends at South pole.
- That means magnetic field lines are the closed curves.
- Where the magnetic field lines are crowded there is strong magnetic field.
- And where the magnetic field lines are more distant there is a weak magnetic field.
- No two magnetic field lines cross each other.
Right hand thumb rule:
According to right hand thumb rule, if we stretched right hand such that thumb is outstretched and fingers are curled around it. Then the curled finger gives the direction of magnetic field and thumb gives the direction of current.
Magnetic field due to a current through a circular loop:
Fig, magnetic field produced due to circular loop
- The magnetic field produced at every point of a current carrying circular loop in the form of concentric circles and the loops become larger and larger as we move away from the wire.
- If the circular coil has n turns then the magnetic field produced is n times larger than the field produced by single turn.
- Because current in each circular turn has same direction and hence filed due to each turn get added.
Magnetic field due to a current in solenoid:
- Solenoid is the cylindrical shaped coil on which many number of circular turns of insulated copper wire are wrapped closely.
- The magnetic field lines in the solenoid are in the form of parallel straight lines. Which means the magnetic field inside the solenoid at every point is same.
- And hence we can say that the magnetic field inside the solenoid is uniform.
Fig. magnetic field produced in a solenoid
Force on a current carrying conductor in a magnetic field:
- Fleming’s left-hand rule gives the direction of the motion or force acting on the conductor.
- According to Fleming’s left-hand rule, if we stretched out thumb, forefinger and middle finger of our left hand in a such way that they are mutually perpendicular to each other then if the forefinger is giving direction of magnetic field and middle finger is giving the direction of the current then the thumb gives the direction of motion or the direction of the force acting on the conductor.
Electric motor:
Principle:
- The principle of electric motor is based on the magnetic effect of electric current. According to which when a current carrying coil is placed in magnetic field then there will be force acting on the coil which rotates it. This is the principle of electric motor.
- Electric motor is a rotating device which converts electrical energy into mechanical energy. The figure shows the labelled diagram of simple electric motor.
Fig. electric motor
- In electric motor, split rings act as a commutator which reverse the direction of flow of current through the circuit. Due to reversing the current direction the magnetic force also gets reversed. And hence the coil is rotating continuously.
- Electric motors are used in water pumps, electric fans, washing machines, electric mixers etc.
Electromagnetic induction:
- Electromagnetic induction is the phenomenon of producing electromotive force by changing the magnetic field around the electric conductor and vice versa.
- In current lamps, electric generators, induction cooking, induction motors, induction sealing the phenomenon of electromagnetic induction is used.
Fleming’s right-hand rule:
- Fleming’s right-hand rule gives the direction of current induced in the conductor.
- According Fleming’s right-hand rule if we stretched out thumb, forefinger and middle finger of right hand in a such way that they are mutually perpendicular to each other. And if forefinger gives the direction of magnetic field, thumb gives the direction of the motion of the conductor then middle finger gives the direction of the motion of the conductor.
Electric Generator:
Principle:
- The electric generator works on the principle of electromagnetic induction. When a straight conductor is continuously moved in a string magnetic field then current is induced in the conductor.
- By using this phenomenon in electric generator, mechanical energy is used to rotate the conductor in a magnetic field to produce electricity.
Fig. Electric Generator
Domestic electric circuits:
- Fuse wire is a safety device connected in series in electrical circuits to protect the circuit from the extra current flow. The rating of the fuse wires is fixed.
- When the extra current greater than the rating flows through the circuit, due to which fuse get heated and meals to break the circuit and protect the electrical appliances from damaging
Following are the precautions taken to avoid the overloading of domestic electric circuit:
- We don’t have to connect many electric appliances to a single socket and avoid to use them at same time also.
- The appliances having some faults or damage we have to not connect them in the circuit.
- And we have to use fuses of proper rating in series with the circuit which protect the whole circuit and also electric appliances.
- Also, we have to use earthing system so that we get protected from severe shock.
Alternating Current:
- In AC currents, charge flows in both direction that is AC current changes its direction periodically and hence it is also called as bidirectional current.
- In India frequency of AC is 50 Hz.
Fig. AC current
Direct Current:
- In DC current charge flows only in one direction and hence it is also called as uni-directional current.
- Frequency of DC current is zero. The magnitude of DC current is fixed or constant. DC circuit possesses mostly register only.
- The power factor for DC circuits is always 1.
Fig. DC current