A Rheostat is a variable resistor.  The term rheostat was coined by Sir Charles Wheatstone.  It comes from two Greek words. Rheos, meaning stream and Stat, implying a regulating device.

The Rheostat is used to limit the current in an electric circuit.  The Rheostat is mostly wirewound with a slider moving over it.  The Rheostat is used for speed control of motors and other electric devices.

The terms rheostat and the potentiometer are often used interchangeable.  In principle, they are similar.  However, there are some differences.  The rheostat has a higher wattage and current rating.  It is used for current control.  The potentiometer, on the other hand, is used to control voltage in circuits.  Its rating is also lower.


The core of a Transformer is made of a number of steel sheets which are placed one on top of another.  These sheets are laminated to prevent losses due to eddy current.

During the operation of the transformer, these sheets get deformed temporarily due to the magnetic flux.  This phenomenon is called magnetostriction.  Over long periods of time, due to repeated movement, gaps form between the surface of the sheets.

These gaps affect the magnetic circuit of the transformer circuit.  This causes a reduction in the flux of mutual inductance.  The transformer current increases by about 10 percent.

The gaps in the core sheets also distort the flux lines and cause an increase in the leakage flux.  This leakage flux causes eddy current heating in metallic components of the transformer such as the tank and other fixtures.  This causes the current to increase by another 5 percent.

This causes an overall reduction in transformer capacity.


The magnetic circuit of an inductance consists of air and iron.  That is, the magnetic flux passes through the air as well as the iron.

Thus, the inductance in a wound coil without a core is due to the inductance of air and the iron.  This combination of inductance is called the Aero Ferric Inductance.  


Absorbent Glass Mat is a Fibre Glass material which is used to absorb the electrolyte in batteries. This makes the electrolyte spill proof.

This is a particular requirement for applications such as in aircrafts, ships, hospitals, etc.  The absorbent glass mat also gives flexibility in battery shape design.  Batteries can be made circular or in many other shapes to conserve space.

The Absorbent Glass mat has a low resistance.  The batteries based on AGM (Absorbent Glass Mat) do not require maintenance.  The Absorbent Glass Mat also prevents sulphation (the deposit of sulphates on the electrodes).  This minimizes the need for topping the charge in the batteries.

AGM batteries are also vibration resistant.

The disadvantages of AGM batteries are their high cost.  They also have low specific energy and are sensitive to overcharging.


The Active Material of a battery refers to the materials in a Battery which take part in the charging and discharging process.

The anode, cathode and the electrolyte constitute the active materials in a battery.

For instance, in a lead acid battery, the lead oxide (anode), the lead (cathode) and sulphuric acid (electrolyte) are the active materials.


The Speed  of a CPU determines the number of  calculations which can be done per second.
The CPU speed is different from the speed of the microprocessor.  The CPU is a part of the microprocessor.

Today, microprocessors have more than one CPU.  Dual core and Quad core processors which contain two and four processors.  The microprocessor speed, therefore, can be more than the processor speed as the CPUs can work in tandem and process calculations.

The speed of the CPU is indicated in GHz (GigaHertz)



The Duty Cycle of a Microprocessor is the ratio of the time the signal is high (ON) to the total Clock period.

Microprocessors use a clock to synchronize the different circuits within them.  The clock circuit generates a waveform (usually square).  The signal stays high and the falls low.

The clock period is the time which begins when the signal becomes high, then falls low and then becomes high again.

For instance, a 33% duty cycle implies that the signal will be high for 33% of the clock period.

The duty cycle can be expressed as follows

Duty Cycle = (Pulse Width/Clock Period) * 100


A Clock Generator in a Microprocessor is a device that generates a steady, continuous signal which can be used to time the different circuits in a Microprocessor.

The signal produced by a Clock generator is usually a square wave.  The rising and the falling edge of the waveform is used to time the circuits.

A Clock generator usually consists of an oscillator circuit and an amplifier.  Quartz oscillators are preferred for their consistency (no drift) and stability.


The clock in a microprocessor serves to coordinate the operations of the different parts of a microprocessor.

A clock is basically an oscillator which generates a series of pulses.  The pulses usually are square pulses.    The output of the oscillator goes from low to high and then from high to low.  The clock signal is generated by a clock generator.

The is usually designed using a quartz crystal.  The clock can also be made using LC and RC circuits.  Quartz offers stability and consistency(no drift) and is therefore preferred.  

The circuits of the microprocessor can be designed to become active either during the rising edge or the falling edge.  

The Speed of the clock will be in MHz or in GHz.  


The Absolute Unit of Current in the CGS (centimeter, gram, second) system is defined as

The amount of current which when flowing through a wire shaped in the form of an arc with a radius of 1 cm exerts a force of 1 dyne on its center.

This definition provides the relationship between electrical and magnetic units.

The medium is assumed to be air or vacuum.  The permeability of air is assumed to be unity.


ElectroAdhesion is a effect of adhesion produced by an Electrostatic field.  

You would have noticed how pieces of paper adhere to a glass rod or ruler which has been rubbed against a piece of cloth.  Electroadhesion can cause sheets of paper to adhere to one another.

Eletroadhesion is also put to use in printers where the paper is moved using this effect. Eletroadhesion is also used in robotics where tiny robots can be made to climb a vertical surface using electroadhesion.

Electroadhesion can be used as an alternative to vacuum suction in certain situations.

Electroadhesion sheets have been developed which can be used to hold products.  These sheets find application in industries in conveyors and in stackers.


Bidirectional transducers are transducers in which the electrical quantity can be transformed into a non electrical quantity and vice versa.

Piezoelectric sensors are an example of bidirectional sensors. Force can be converted into an electrical signal. An electrical signal can also be converted into an physical movement or a force.



An inverse transducer is a transducer in which an electrical signal is converted into a non electrical quantity.

An example of an inverse transducer is a piezoelectric transducer in which an electrical signal can be converted into a movement or a vibration.