Magnetic effects of Electric Current:- Part 3

Galvanometer

-> It is a device which detects the current is flowing or not in a closed circuit across the conductor. 

-> It also tells us the direction of the current.

                    

Electromagnetic Induction 

-> The production of Electricity from Magnetism is called Electromagnetic Induction. It was given by Michael Faraday. 

 The difference b/w current and the induced current is that Current is just a normal current which is following through a conductor and the induced current is the current which created due to the influence of variable magnetic field across the conductor. 

Magnetic Force 

-> The force exerted when a current-carrying conductor placed in a magnetic field is called magnetic force. Experimentally, it has been found that the force experienced by the current-carrying conductor in a magnetic field is:- 

     -> directly proportional to the magnitude of the current flowing through the conductor i.e. F∝ I 

     -> directly proportional to the magnitude of the magnetic field of the conductor in a magnetic field i.e. F∝ B 

     -> directly proportional to the length of the conductor in a magnetic field 

         i.e. F∝ L 

     -> directly proportional to the sine of the angle between the conductor and the magnetic field. i.e. F∝ Sin θ 

   So, 

Note:- 

* If θ = 90⁰ i.e. the rod is perpendicular to the direction of magnetic field then the force is maximum. 

         F= BIL Sin θ 

           = BIL Sin90⁰

         F = BIL 

* If θ = 00 or 1800 i.e. the rod is parallel to the direction of magnetic field then the force is minimum. 

         F= BIL Sin θ 

           = BIL Sin0⁰ [Sin0⁰ = 0] 

         F = 0 

Note:- SI unit of a magnetic field is the tesla (T). 

* 1 Tesla- The magnitude of the magnetic field is said to be 1 tesla if a conductor of length ‘one metre’ carrying a current of ‘1A’ experience of force of ‘1N’ when placed perpendicular to the given magnetic field. 

Electric Motor 

-> An electric motor is a device which converts electrical energy into mechanical energy. Two types of motor that we use in our day to day life are:- 

 (i) AC motor e.g. motor of a fan 

 (ii) DC motor e.g. motor of battery-operated toys 

Principle:- it is based on the principle that when a current-carrying conductor moves freely in a magnetic field then it experiences a force and begins to moves in a particular direction which was given by Fleming's left-hand rule. 

               

e.g. Electric fans, Refrigerators, Washing machines, Mixers, etc. 

Working of Electric Motor

 

* Armature coil- it consists of a large number of turns of a rectangular coil ABCD made of copper wire wound over a soft iron laminated core. The soft iron core becomes magnetised and increase the strength of the magnetic field. This makes them motor make powerful. 

Note:- The coil is placed perpendicular to the magnets. 

* Commutator- A device which changes the direction of current through a circuit is called commutator or split ring or half-ring. It changes the direction of the current flowing through the coil after every half rotation of the coil. 

* Strong Field Magnets- Two permanent magnets are placed. 

* Brushes- Two carbon brushes are kept in such a way that they make a contact with the split rings. 

Working

-> The current from the battery enters the coil through left brush B1 and left half-ring C1, goes around the coil and then leaves through the right half-ring B2 and right brush C2. 

  According to Fleming’s left-hand rule, the directions of the forces on the two sides AB and CD of the coil are shown in the above figure. The force on AB acts inwards whereas the force on CD acts outwards. As a result, A torque is applied to the coil that turns it. After that, the half-ring momentarily loses electrical contact with the brushes, so that there is no current in the coil and no applied torque. 

    However, like any moving object, the rotating coil does not stop immediately due to its inertia of motion that carries it onward. When the half-ring re-establish contact with the brushes, there again is a current in the coil and a magnetic torque again rotates the coil in the same direction. This time the force on AB acts or outwards and that on CD acts inwards and also the rings are in contact with different brushes. Ring R1 comes in contact with brush B2 and ring R2 to comes in contact with brush B1. 

   The split ring ensures that the current is reversed through the coil after the half revolution to yield a torque that produces a continuous rotation of the coil. 

Note:- The sides AB and CD are perpendicular to the magnetic field hence they experience a force whereas the sides BC and AD are parallel to the magnetic field, therefore, they do not experience a force. 

 The speed of the motor depends on:- 

 -> Directly proportional to the number of turns in the coil i.e. Speed ∝ n 

 -> Directly proportional to the strength of the current i.e. Speed ∝ I 

 -> Directly proportional to the strength of the magnetic field i.e. Speed ∝ B

 

Difference between AC & DC

AC	DC
1. AC is safe to transfer longer distance even between two cities and maintain the electric power.	1. DC cannot travel for a very long distance. It loses electric power.
2. The rotating magnets cause the change in direction of electric flow.	2. The steady magnetism makes DC flow in a single direction.
3. The frequency of AC is depended upon the country. But, generally, the frequency is 50 Hz or 60 Hz.	3. DC has no frequency or zero frequency.
4. In AC, the flow of current changes its direction backwards periodically.	4. It flows in a single direction steadily.
5. Electrons in AC keep changing its directions – i.e. backwards and forward.	5. Electrons only move in one direction – i.e. forward.

Graphical representation of AC and DC

                         

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