D.C. MOTOR

A direct current motor (d.c. motor) can rotate in one direction continuously. D.C. motor consists of the following parts :-

• A permanent magnet
• A pair of carbon brushes is fixed to push against the commutator. The carbon brushes are connected to a d.c. power supply or batteries.
• An armature which is a rectangular coil bound to a soft-iron core that is placed between the poles of permanent magnet. The framework of the armature is join to an axle.
• The ends of the coil are connected to a pair of copper half-rings called a commutator (half-rings)
  

Step 1 : At the start the coil rotates as the current flow.

Step 2 : When the coil is at the vertical position, the coil keeps turning due to inertia.

Step 3 : When the coil passes the vertical position, the contacts between the half-rings & the brushes interchanges. Current in the coil is reversed. The magnetic forces acting on the coil is reversed. The coil keeps on rotating in the same direction.

Note that the commutator and the carbon brushes are arranged in such a way that the direction of the current flowing through the rectangular coil is reversed in each half of a revolution of the armature. Hence, the rectangular coil continues to rotate in the same direction.

Factors that affect the speed of rotation of a d.c. motor are :-

• The strength of the permanent magnet
• The magnitude of the current
• The use of laminated soft-iron core
• The number of turns of the coil

TRANSFORMER

Devices that increase or decrease the voltage of alternating current. Consists of 2 coils wrapped around an iron core. The two coils are insulated in such a way that no current can flow from one coil to the other. AC current passes through first coil, inducing a current in second wire. The phenomenon of changing the current in a coil to induce a voltage and a current in another coil is called mutual induction..



Types of Transformers

Step-up transformers (Increases Voltage)


Is a transformer which has the output voltage greater than the input voltage due to Ns > Np.


Step-down transformers (Decreases Voltage)


Is a transformer which has the output voltage smaller than the input voltage due to Ns < Np.


How to build a simple transformer??


In figure above, the primary coil is connected to an a.c. power supply and the secondary coil is connected to a load such as a light bulb.

ELECTROMAGNETIC INDUCTION

An electromotive force (e.m.f.) will be induced in a conductor when the conductor moves through a magnetic field. This effect is called electromagnetic induction. According to Faraday,s Law, the size of the induced e.m.f. is proportional to the rate of change of the magnetic field. Reversing the direction of movement of the conductor will cause the induced e.m.f. to produce a current in the opposite direction. The direction of induced current can be determined by using the Fleming’s Right Hand Rule.



Induced current in a solenoid…

When a magnet bar is thrust into a coil connected to an electric circuit, it causes a current to flow in the circuit to which the coil is attached.





When the magnet is withdrawn, the direction of current is reversed..



Lenz’s Law states that the induced current always acts to oppose the action producing it.

ROBOTIC DESIGN

source : robotic design studio sites



Programmable bricks. The top device is a cricket, which is about the size of a 9 volt battery. The bottom device is a Handy Board, a palm-sized robotic computer. The devices & LEGO figure are shown at roughly the same scale.

Traditionally, engineering courses have had little or no place in a typical liberal arts education. A standard argument is that engineering does not belong in a liberal arts curriculum because it is too practice and detailed oriented. The purpose of liberal arts education is to give students the necessary set of intellectual tools to live fulfilled lives, not to give a narrow professional training…

For more information...
Log on http://www.wellesley.edu/Physics/Rberg/papers/RDS-JSET-final.pdf




Inspired by a visit to a local auto wash, the 6 foot long Rubber Ducky’s Wash featured soap bubbles generated by fans blowing on a bubble wands, gentle mists of water supplied by LEGO driven aerosol cans and a visually spectacular buffing action provided by colorful felt brushes.

For more information...
Log on http://www.wellesley.edu/Physics/Rberg/papers/RDS-JSET-final.pdf