CHAPTER 4 MAGNETIC EFFECTS OF CURRENT
Field lines are used to represent a magnetic field. A field line is the path along which a hypothetical free north pole would tend to move. If the field lines are closer, it means that the magnetic field is greater.
MAGNETIC FIELD DUE TO CURRENT
A metallic wire carrying an electric current has a magnetic field associated with it. The field lines about the wire consist of a series of concentric circles whose direction is given by the right-hand rule.
The right hand rule: If you are holding a current carrying conductor in your right hand such that the thumb points towards the direction of current, then you fingers will wrap around the conductor in the direction of the field lines of the magnetic field.
FORCE ON A CURRENT-CARRYING CONDUCTOR IN MAGNETIC FIELD
A current carrying current in a magnetic field experiences a force on it whose direction can be found out by Fleming’s left hand rule. According to this rule, stretch the thumb, forefinger and the middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic and the second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.
An electric motor is a rotating device that converts electrical energy to mechanical energy.
The changing magnetic field in a conductor induces a current in another conductor is called electromagnetic induction.
The direction of induced current in a conductor can be found out using Fleming’s right hand rule. If you stretch the thumb, forefinger and middle finger of right hand so that they are mutually perpendicular to each other, the forefinger indicates the direction of the magnetic field, the thumb shows the direction of motion of conductor and the middle finger shows the direction of the induced current.
In an electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity.
DOMESTIC SUPPLY OF ELECTRICITTY
In our houses we receive AC electric power of 220 V with a frequency of 50 Hz. One of the wires in this supply is with red insulation, called live wire. The other one is of black insulation, which is a neutral wire. The potential difference between the two wires is 220 V. The third wire is the earth wire that has the green insulation and this is connected to a metallic body deep inside earth. It is used as a safety measure to ensure that any leakage of current to a metallic body does not give any severe shock to a user.
A fuse in a circuit prevents damage to the appliances and the circuit due to overloading. Overloading can occur when the live wire and the neutral wire come into direct contact or there is a fault in any appliance. In such a situation, the current in the circuit abruptly increases. This is called short-circuiting.
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