Effect of resistor

Lets see how resistor affect the circuit.

Things needed:

• Resistor- 470Ω,1kΩ,2.2kΩ.
• LED
• 9V battery
• Bread board
• Wires

Setup the circuit as shown below:

The circuit is setup in the breadboard as shown below:

Note the intensity with which LED glows. Replace the 2.2kΩ with 1kΩ. You will notice that LED glows brighter compared to the previous configuration! Replace the 1kΩ resistor with 470Ω resistor. LED glows brightest of the previous configurations.

This shows that, as the resistance of the circuit decreases, the current in the circuit increases! That implies that resistor acts as a hindrance to the flow of current through it.

Please feel free to ask doubts by ‘comments’.

Breadboard

Breadboard is a base for constructing electronic circuits. Its is used for testing the circuit i.e it used for building prototype of a circuit. It consists of plastic block with holes and nickel alloy strips under these holes. Breadboard is shown below:

The connection inside the breadboard is shown below:

Black lines shows the way in which nickel strips are placed inside. These strips acts as wires. The electronic componets(like resistor, led, capacitor, wires etc) are inserted in these holes.
When the prototype of the circuit gives the desired result, it is then tranferred to PCB(Printed Circuit Board), which is a permanent one.

LED

LED- Light Emitting Diode.


It’s consists of a semiconducting material which emits light when current is passed through it. It can emit light of different colour. When voltage is applied, it causes the hole present in p-side and the electron present in the n-side to move towards the space charge region. When hole and electron combine it emits photon. The wavelength of the photon(i.e colour of the light) depends on the band gap energy of the semiconductor used. An LED is shown below:

LED

It has lot of advantages over the incandescent lamp. LED is more efficient, less power consuming; less heat emitted etc. therefore it is ideal for electronic circuits since it consumes less power.

The shorter terminal is usually the negative terminal and the longer terminal is the positive terminal. The current passing through it must not exceed the limit stated by the manufacturer.

LED has many applications such as lighting, monochrome Message Boards, Bar Code Readers, color & Money Sensors etc.

Resistor

Resistor,as the name says,  it resists. It is a device which decreases the flow of charges passing through it, thus reducing the current in the circuit. It has two terminals,  one for the current to enter and  the other for it to exit. Symbol of resistor is shown below:

The important characteristics of resistor are:

Resistance: It refers to the degree to which the resistor opposes the flow of current. The unit of resistance is ohm and the symbol is Ω.

Working voltage: It refers to the voltage that can be given to a resistor for proper functioning.

Resistance to temperature change: It is seen that the resistance of a material varies with the variation of temperature. A good resistor should show little or no change of resistance when subjected to temperature change.

Low noise: Noise refers to fluctuation of current. So a resistor should produce low noise, that is current  passing through it should not vary much.

Inductance: When current varies in the circuit, there is an induced emf (electro motive force) produced in the opposite direction to the flow of current. Thus a resistor should have low inductance value so that current and voltage will not lag.


Types of resistors:

Carbon resistor:

They are made of finely powdered carbon and ceramic powder. The ratio of the mixture determines the value of resistance. Higher the concentration of carbon, lower the resistance. They come usually in the shape of cylinder and there is a metallic wire on each end which can be used as terminals. The resistance of this type of resistor can be determined by the colour code.

They are cheap and used for general purpose.

Disadvantages:

• Poor stability.
• Poor thermal coefficent.
• Open ciruit problem due to:
• Burning of resistor due to heating.
• Breaking of resistors due to thermal stress.

Wirewound resistor:

A thin wire (usually tungsten or manganin)  is wound on a non-conducting material (usually cement or porcelain) in the form of helix. Resistors of this type range from 0.1Ω to 100kΩ. They can handle higher value of currents than the normal resistors of the same value of resistance.

The problem with these resistors is that they also act like inductor (as well as resistor) when they are used in AC circuits. Since the coil is wound in the form of helix, it has some inductance. For use in AC circuits, special non-inductive wirewound resistors are available.

Film resistor:

There are different types of film resistors like metal oxide film, metal film, carbon film, thick film resistors. They are made by depositing a pre metal on the insulating material (usually ceramic) and then using laser to cut the deposited metal in the form of spiral helix.
This type of resistor has low tolerance value compared to carbon resistors.

Metal oxide film resistors have better surge current capability and higher temperature rating than the carbon resistor equivalent. Metal resistor have better temperature stability, lower noise and stable for higher frequency applications compared to carbon resistor equivalent.

Disadvantages:

• High noise
• Open circuit problem due to
• High temperature causes breakdown of resistors.
• Scratching of film.

Colour code

Resistance of a resistor can be found out using colour code.

Hope the above animation, illustrates how to read the value of resistance of a resistor.


Please feel free to ask any doubts about this topic, by 'comments'.

What a circuit is?

First let me tell you guys, what exactly a circuit is!
Well.. circuit is a combination of power supply, load and wires connecting them. Power supply can be either from a battery or directly from the mains. It can be either supply of current or voltage. Load maybe a device or combination of devices such as resistor, inductor, capacitor, diodes, that consumes power.

When a low level current/voltage is given to the circuit, it becomes an electronic circuit. e.g motherboard, amplifiers, cell phones. If the current/voltage given to the circuit is high, then it becomes an electrical circuit. e.g fan circuitry, motor circuitry.

Technically, power supply, load and wires are referred as active components, passive components and transmission lines respectively.