Mechanical to Electrical Energy
When a current carrying is placed in a magnetic field, each of the moving charges, which comprise the current, experiences the Lorentz force, and together they can create a macroscopic force on the wire (sometimes called the Laplace force).
Working of the electric motor:
Current in the coil ABCD enters from the source battery through conducting brush X and flows back to the battery through brush Y. Notice that the current in arm AB of the coil flows from A to B. In arm CD it flows from C to D, that is, opposite to the direction of current through arm AB. On applying Fleming’s left hand rule for the direction of force on a current-carrying conductor in a magnetic field (see Fig.2). We find that the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards. Thus the coil and the axle O, mounted free to turn about an axis, rotate anti-clockwise. At half rotation, Q makes contact with the brush X and P with brush Y. Therefore the current in the coil gets reversed and flows along the path DCBA.
The reversal of current due to the split ring commutator, also reverses the direction of force acting on the two arms AB and CD. Thus the arm AB of the coil that was earlier pushed down is now pushed up and the arm CD previously pushed up is now pushed down. Therefore the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.
The inside of the electric motor looks something like this:
DC Electric Generator:
It works on the principle of electromagnetic induction. When a coil is rotated in a magnetic field, an EMF is induced in the coil.
Working of the electric generator:
When the armature coil is rotated in the magnetic field with constant angular velocity ω, θ (=ωt), the angle between magnetic field B and are vector A changes with time. Magnetic flux associated with the coil changes and EMF is induced in the armature coil.
By Faraday’s law, induced EMF at any instant
The EMF attains its peak values when the plane of the coil is parallel to the plane of the magnetic field. The EMF is zero when the plane of the coil is perpendicular to the magnetic field.
5) Induced Current:
To get a direct current (DC, which does not change its direction with time), a split-ring type commutator must be used. With this arrangement, one brush is at all times in contact with the arm moving up in the field, while the other is in contact with the arm moving down. We have seen the working of a split ring commutator in the case of an electric motor. Thus a unidirectional current is produced and the generator is called a DC generator.
6) Law of conservation of energy :
As in our previous energy conversion project, the law of energy conservation is applicable. The law states that:
Energy can neither be created nor be destroyed but can be converted from one form to another. This theorem can also be restated in the form of the First law of thermodynamics.
Hence the electrical energy used to light our LEDs can be taken as the transformed electrical output to the mechanical energy input.
Conclusion:
This project was primarily an effort to apply my theoretical knowledge attained from school classrooms to a small working model created solely to spread awareness about physical sciences among the juniors with some scientific entertainment.
Our primary conclusion is that the mechanical energy used in rotating the rotor blades is converted to electrical energy and the law of conservation of energy.
In the this process we have also reviewed the definition of magnetic flux and have observed the application of Faraday’s law of electromagnetic induction and Lenz’s law.
We have also utilized the electric motor as an electric generator producing a DC electrical output (of 1.5 Volts) that lights our LEDs. Meanwhile, the working principles of the DC electric motor and generator have also been refreshed in our memories. Finally, the law of conservation of energy has been verified as we observe the mechanical to electrical energy conversion.
References:
1) Definition retrieved from chapter 6 “Electromagnetic Induction” NCERT Physics textbook for class 12 (Part 1).
2) Referred from chapter 6 “Electromagnetic Induction” NCERT Physics textbook for class 12 (Part1).
3) Referred from chapter 6 “Electromagnetic Induction” NCERT Physics textbook for class 12 (Part1).
4) Referred from chapter 13 “Magnetic effects of electric current” NCERT Science textbook for class 10.
5) Figure-2 retrieved from –http://studyvilla.com/dcmotor.aspx
6) Figure-3 retrieved from -http://en.wikipedia.org/wiki/Electric_motor
7) Figure-4 retrieved from - http://www.tutorvista.com/content/physics/physicsii/electricity/electric-generator.php
8) Graph-1 retrieved from- http://farside.ph.utexas.edu/teaching/302l/lectures/node91.html
9) Referred from chapter 13 “Magnetic effects of electric current” NCERT Science textbook for class 10.
10) Definition retrieved from chapter “Thermodynamics” in the grade 11 NCERT textbook for Physics (Part 2).