Common Base configuration of BJT (Voltage amplification)

In this type of configuration we have, the Base terminal of BJT is common with both input and output. Where input is provided to the Emitter and output is collected from the collector. The circuit of the configuration is shown in the figure below. This configuration is used for the voltage gain and current buffer. And we have an input impedance that is low and output impedance is high.

Application

Common base the configuration is not used for the low-frequency input signal and for low frequency operating circuit. Though it is used when there is low input impedance is connected or present. Such as preamplifier, in a where we have low signal and we have to strengthen it out. So there we use a common base configuration.
While mainly it is used for very high frequency and ultra-high frequency. It is because its input capacitance does not affect by the amplification process. Due to which high frequency does not degrade or change.

Circuit:

As you can see in the figure, that base is common with input and output, while Emitter is connected to the input, and the collector is connected to the output. There is a battery connected between base and emitter, to forward-biased base-emitter junction. To forward bias we need to connect the positive side of the battery to the P side of BJT and negative side of the battery to the N side of BJT (In PNP case emitter is P side and Base is N side). There is another battery connected between collector and base to reverse biased the collector-base junction. To do this we have connected the positive side with the base and negative side with the collector.

Working:

Current Gain

Let’s first see the current flow in this configuration. We all know that current flows from the positive terminal of the battery to the negative terminal of the battery. So, in this case, current I_E flows from V_BE towards the emitter, from there some of the current flows towards the base region which is I_B and remaining all the current goes towards the collector. So we can recall the equation,

I_E = I_B + I_C

I_E is the input current and I_C is the output current. So this equation shows that output current I_C can never be greater than input current I_E. So current gain could never be greater than 1. It will be “1” or “less than 1”.

Current Gain equation will be

$$ α= I_C/I_E , where\ "α"\ is \ current\ gain $$

Using this equation we can find out the current gain of a circuit.

Voltage gain

Now let’s see how it provides us the voltage gain (amplification).

As we have the current gain$$  α=I_C/I_E $$ 
And resistance gain              $$ = R_L/R_I_N , $$ So using Ohm’s law(V=IR), We get,
Voltage gain= Current gain x Resistance gain
Voltage gain = $$ I_C/I_E × R_L/R_I_N = {I_C R_L}/{I_E R_I_N} $$

So this equation shows that we can get the desired voltage gain by changing the amount of input and output resistance.

Input characteristics

Now let’s see what the input characteristics of the common base configuration are. Means when we change input voltages V_BE what effects does it has on input current I_E. And keeping the output voltage V_CB constant. We will plot a graph having V_BE on the x-axis as we are changing V_EB that’s why it is on the x-axis. While I_E will be on the y-axis. We will see that there is no current across input when V_EB is 0 to 0.6V. Because the starting voltage of the diode is 0.7V. So when V_EB cross 0.6 V. The I_E will start to grow up and will grow larger with small increase in voltage V_EB. So one case was with V_CB voltage was kept constant at 5V. Now observe another case with V_CB at 7V, and then with 10V. And at last plot a graph of all 3 cases as shown in the figure below.

Output characteristics

Now observe the output characteristics. We will change the output voltage V_CB and observe the change in output current I_C, with input current I_E will remain constant. So V_CB is on the x-axis because we will be changing it and I_C on the y-axis because it will be changed. We will observe that when we keep I_E constant at 0 and will change V_CB, it will have no effect on the I_C. I_C will remain zero at every value of V_CB (0V, 3V, 5V etc). While when we keep I_E constant at 1mA and change V_CB, then we will see I_C will come near to 1mA will remain constant for further increase in V_CB. Now keep I_E constant at 2mA, we will see that after changing V_CB, I_C will come near to I_E, means near to 2mA and will go constant for further increase in V_CB.Will draw plot for all the experiments. And we observe that I_C will never be greater than I_C. As equation 1 tells that.

Bipolar Junction Transistor(BJT) as a Amplifier

Amplification

As we have discussed the other uses of BJTs in previous posts, now there is another main use or advantage of Bipolar transistor is that it can amplify the input signal whether it is voltage or current. As some time we need to amplify the current and sometimes voltage. We provide an input signal to the BJT, and it produces the amplified signal at the output. The gain of the amplifier can be calculated by the ratio of output to the input value of current or voltage. The amplifier does not change the waveform or frequency. It just affects the current and voltage.

How to make BJT an Amplifier:

To make BJT work as amplifier we need to do some different types of configuration of it, in a circuit. There are three configurations, which we can do,

•        Common Base Configuration (only has voltage gain).
•       Common Emitter Configuration (has both voltage and current gain)
•       Common Collector Configuration (only has current gain)

Bi Polar Junction Transistor (BJT): Introduction, Construction and Working

Introduction:

BJT stands for Bipolar Junction transistor which means two polar junctions. The reason it is called Bipolar is that it uses both electrons and holes for carrying charge or to flow the current. While FET is known as a unipolar transistor.

Construction:

As we have discussed diode before, and how it is formed by the junction of two regions, P doped region, and n doped region. The BJT is formed by the combination of two back to back diodes. The Bipolar junction transistor or BJT has two junctions of the semiconductor. In one of the two types (PNP), a thin n-region is shared by two p-regions. And in another type (NPN), a thin p-region is shared by two n-regions, the figure below explains this.

          Fig (a)

                                                                                 Fig (b)

                                   

This complete structure of BJT has three terminals and has three layers. Each terminal for each layer. And the names of these layers are Emitter, Base, and collector shown in above figure. For NPN the arrow is going away from the Emitter terminal and for PNP the arrow is towards the emitter terminal. The reason is explained later.

 Functions of BJT:

BJT can be used for three purposes,

• Current controlling
• switching
• Amplification

Controlling Current:

BJTs are mostly used for controlling the amount of current flows from emitter to collector or collector to base. These are two cases for two different types of BJT (which are PNP and NPN). In PNP the current goes from Collector to emitter with the combination or addition of base current, see fig (a). While in NPN the current goes from Emitter to collector with separation or removal of base current see fig (b). In all this, the current which goes from emitter to collector or collector to emitter is the controlling current and the current which goes or comes from the base is controlled current. Now all this statement means that, the amount of current which have to go from emitter to collector in NPN transistor is decided by or controlled by the current flows towards the base as shown in the below picture.

           Fig(c)

                                                                                    Fig(d)

         

                                                                                          

Equations of current:

This thing also produce the equation of current,

I_E = I_B + I_C

Where I_E is the Emitter current, I_B is the base current and, I_C is collector current.

I_B = I_E - I_C

I_C = I_E - I_B

Transistor: Introduction, importance and history

Introduction:

The name “Transistor” has come from the two words “Transfer” and “Resistance”. Which then were combined into “Trans-resistance” and after that it was contracted to name as “Transistor”. From its origin words “transfer of resistance”, its process comes. Which is that the current passes from the low resistance portion to the high resistance portion for amplification.

                                                       

Definition:  

“Transistor is a semiconductor device which is used to do the switching and amplifying of electronic signals.”

Means if you want to do switching in electric circuit like, to stop the flow of current at a point at particular condition then transistor is the best you got. Or if you want to amplify your input signal like if you want to increase the loudness of input voice then transistor can do this. These are the main uses of Transistor.

 History:

Before Transistor there was Vacuum tube which was the main or important component of electronic devices. But it was big in size have low efficiency, more heat up, high power consumption, required high voltages and current, and have complexity in circuits. Then there were ideas of Field effect transistor started to come in 1905. And then in 1947 John Bardeen and Walter Brattain and William Shockley (Group leader) invented the first complete transistor named as “point contact transistor”.  And then the first commercially available transistor came in 1960s.

Importance of Transistor:

Honestly! I will say in electric area the most useful thing we have now a days is transistor. Transistor is the building block of all the electric devices. We are getting now a days more smaller devices is just because of transistors as they have very small size. They are so small that we rarely found an individual transistor. They are found in integrated circuits in large numbers. An IC normally contain 20 to 60 transistors. The latest microprocessor contain almost 3 billion transistors and you can imagine the size of microprocessor. They are in our smart phones, smart watches, and radios and in every small smart device. The reason for their large use is their less cost and their requirements of low currents and voltages for operating.

Types of Transistor:

There two main types of Transistor,

1. BJT Transistor (Bi Polar Junction)
2. FETs Transistor(Field Effect Transistor)

BJT transistor are further classified to:

1. n-p-n
2. p-n-p

While FETs have also further classification.

The transistor tree below show classification of these Transistors.

                               

    

What is Charge, current, voltage? Definition explanation

Charge

Definition:

“Charge or Electrical charge is the property of, unit of a matter”

Explanation:

Charge does not physically exist; this is only a theoretical word. Yes, we use the word charge physically in many topics, just to describe the topic by taking a simple or basic thing (charge). Charge tells that how the matter will react with the other matter or in a magnetic field or in a electric field.

A matter is named as charge, only when there is a difference in number of electrons and number of protons in atom of that matter. If there are more electrons than proton in atom then it is negative charge and if there are more protons than electrons then it is positive charge. Hence this is two types of charge negative and positive charge.

Unit:-

The unit of charge is Coulomb and represented by q. 

Current

Definition:-

“Current is the rate of flow of electric charges.”

Explanation:-

Current is the flow of electric charges which is free electrons. Current flows in a circuit when there is pressure or some force applied to the charges in a circuit. Current flows from negative end to towards positive end. Rate of flow means, how much charges will flow in some fix time. There are two types of current. AC and DC.

AC means alternating current. The current which changes its direction of flow after half interval is known as alternating current.

DC means direct current. The current which flow in only one direction is known as DC current.

Each type of current has its own application.

Unit:-

Unit of current is A Ampere.

“When one coulomb charge will flow in one second through some point, then current will be one ampere.”

 Voltage

Definition:-

“Voltage is a force or pressure which causes the charges to flow through circuit.”

Explanation:

As we discuss in explanation section of current that , current flows through the circuit when some force or pressure applied to the charges in circuit. That force and pressure is Voltage. It is also known as potential difference. In some words, Voltage is the power of current. Means with how much power the current is flowing. The more the voltages the more the rate of flow of current in a circuit.

Unit:

Unit of voltage is V volt.

Electric Potential: definition, explanation, example.

Definition:

"Electric potential is the amount of word done in moving a point test charge from its original position(reference position) to some specific point or position, while moving the charge in direction opposite to direction of field in which charge is present."

Explanation:-

The definition above seem to be difficult to understand the electric potential but I will explain it briefly.
Consider their is a positive point charge A, which have its own electric field around it. And there is another positive test charge B which has no electric field.

 When we will move the test charge B towards the electric field of point charge A then test charge B will move away from the point charge A. This is natural that charge always move from high potential to low potential.

low potential is the area where the charge feels less force while high potential is the area where the force is high.

So to move charge, against its natural movements. we have to provide electric potential or force or to do work. To move test charge B towards the charge A we have to apply some potential which is electric potential, to move the charge from low potential to high potential. So charge B will gain potential energy while moving towards high potential from low potential.

Electric potential is the basic studies of charges behavior with each other. So if you feel there is some type of confusion feel free to comment. The post will be update!

Ampere's law: explanation, definition, formula

Definition:-

"Ampere's Law states that magnetic field around a conductor in which electric current is flowing, is directly proportional to the amount of electric current flowing through conductor."

Explanation:

Ampere's law provide us method or formula to calculate magnetic field, produced by electric current.
Just like electric field is directly proportional to the amount of charge, the magnetic field is directly proportional to the amount of electric current from which it is producing.

Formula:-

The most difficult in ampere's law is to derive its equation or make the formula for calculating the magnetic field around a long conducting wire.
So let's start this,
Consider we have long straight conducting wire, when electric current flows through it, the magnetic fields produces around the wire in concentric circle. As shown in below pic.

Every circle is for some specific part of wire and as we move forward in wire, the distance between these circles increases, that mean magnetic field is decreasing. Direction of magnetic field can be found by Fleming's right hand rule.(with direction of current giving)
Now to make the formula, consider there all the parts of wire( which have there magnetic field circuit) having length L and there magnetic field around these parts or elements is B for (every part).

So the equation will become,

And after removing proportionality,

where 𝝁 is the premiability of material or conductor.
B is the magnetic field and delta L is the sum of all length parts and I is the current flowing through the conductor,
sigma shows that the sum of all the length elements or parts with their magnetic field.
Where delta L could be replace by 2πr for particular(single part) length element.
So Then magnetic filed would become,

Gauss's Law: definition, explanation, formula

Definition:

"Gauss's Law states that, Electric flux around a closed surface is depends upon charged enclosed in that surface and permittivity of free space."

Explanation:

Gauss's law states tell us about electric flux through some closed surface or area,
Electric flux through some area depends upon the charge enclosed by that area and the permittivity of free space in that area.
consider there is a closed sphere and there is charge enclosed in it, the flux out of it or the electric field out of the whole area could be determined with the help of Gauss's law.

Consider we wan to find the electric flux through the green planer area, then it will be simple that electric field lines multiplied by area perpendicular to the lines.

But when there comes a closed surface then there is nothing best except Gauss's law to find electric flux through closed surface (enclosed charge.)

It is not necessary that the surface should be closed sphere it could be any type of closed surface. And we will use Gauss's law to determine the electric flux through it.

Formula:

Mathematically we can determine the electric flux through closed surface by formula,

Where Q is the amount of charge enclosed and Ɛ is the permittivity of free space and 𝛟 is electric flux through the surface.

Electric Charge density, definition, explanation

Definition:

"Electric charge density is the amount of charge on unit volume space or surface or area."

Explanation:

Electric charge density is the density of charge on unit area, the charge could be less or  more, and charge could be positive or negative.
as shown in figure 1 below, in which there is positive charge on surface but less and on figure 2, there is more positive charge.

So area in figure 2 have more electric charge density than figure 1.

The area or volume could be one dimensional, two dimensional and three dimensional. 

Formula:

The electric charge density can be written in the form,

Where p is the charge density and q is the amount of charge and v is the volume of space and unit area. we can replace the v by A, when there is unit area.

Capacitive and Inductive Reactance and their explanation

Capacitive Reactance:-

"Capacitive reactance is the resistance offer by capacitor to the current."

Explanation:-

Whenever there is current flows through the capacitor there is the opposition offer by it to the current, which causes delay in its charging. And its this reactance depends upon the frequency of AC current flowing through it. the more the frequency the less its reactance will be and less the frequency the more the reactance will be. The formula for the capacitive reactance is below.

Inductive Reactance:-

"Inductive reactance is the resistance offer by inductor to the current flowing through it."

Explanation:-

When AC current flows through the inductor it offer some resistance to the current. it depends upon the frequency of current. The more the frequency the more the reactance and less the frequency less the reactance. This behaviour is of inductor when AC current flows through it.

Power, its definition, explanation, formula, unit

Definition:-

"Power is define as rate of doing work or Work done per unit time."

Explanation:-

Power is the doing some work, taking less time. Power depends upon doing work and time taken to complete the work. A person have more power will do more work but take less time and person have less power will do less work but will take more time. So this is the concept of power. Work does not depend upon time while power depends upon. so this is the only difference between them.

Formula:-

The formula for power is work done per unit time.

Power = Work / time

as work is equal to 

work = F.d

so power would have,

Power = Force.displacement / time

P = F.d / t

Unit:-

Unit of power Watt  is define as " If one joule of work is done in one second then power will be one watt"

P = F.d / t

Watt= Newton. meter / seconds

Watt = joule / second.

Why like charges repel each other and unlike charges attract each other?

Why like charges repel each other?

"Like charges repel each other because, it depends upon where the two charges have their electric field forces directed."

As positive charge have electric field lines going away from it and when two positive charge particles come near to each other there electric field lines tries to bend each other and their lines of forces are opposite in direction with respect to each other so both particles tries to send away to each other and hence in this way they repels each other.

Below diagram explain all the things which is described above.

Why unlike charges attract each other?

Like charges attract each other because their electric field lines are in the same direction in respective to each other, as we know Negative charge have electric field lines towards it(or coming to each other), and positive charge have away from it or going away from it. so when both comes near to each other, while negative charge tries to attract positive charge and positive charge tries to move towards negative each other.

Below picture explain all the phenomena describe above.

Electric Fields lines and Forces

Electric Fields:-

"Electric Fields are the area or space or region around a body or particle which is charged, in which area it effects(attracts or repel) on other body or particle which is charged."

Explanation:-

Consider their is a charged particle A, it has Electric fields lines, because it is charged. When a unit positive charge(small charge) will come into its field lines then it will feel some force, which is the effect of Charged particle A. It will repel the unit charge (as positive and positive repel each other).

The unit positive charge will only feel this force when it will come into the region where there is Electric field lines of Particle A.

In above diagram unit charge 1 will feel force as it is in the field region of charged particle A, but 2 will not feel any force as it is out of field lines of charged particle A. 

Electric Forces:-

"The force which charged unit positive charge feel when it is in the electric field lines of charged particle (A)."

Explanation:-

As Charged particle have electric field region where it exerts some force on some other charged particle (when it comes in the electric field of that charge). There are two type of forces which is exert by the charged particle in its field region. Attractive force and Repulsive force. Positive charge exert repulsive force on other positive charged while it exert attractive force on negative charge. In general there is attractive forces in opposite charges and there is repulsive force in between like charges.  

In below pic A is positive charge and it is repelling other positive charge.

In below pic, A is positive charge which is attracting negative charge.

Transformer, Definition, Explanation, working, construction, types

Definition:-

"Transformer is an electrical device that converts low voltage into high voltage or high voltage into low voltage."

Explanation:-

Transform the current or voltage, it is used to get high voltage when input is of low voltage and to get low voltage from high voltage.

Transform works on the principal of Mutual Induction, according to which "When alternating current flows through one winding of coil, due changing nature of ac current, there produce an emf across winding and magnetic flux around winding. When another winding of coil comes near the first winding, there is effect of magnetic flux of first winding on second winding and due to AC current as it changes continuously produces changing magnetic flux of first winding and due to this change there causes the EMF in second winding and hence current starts to flow through second winding, so this process is known as mutual Inductance". Transformer works on this principle. As there is no connection between two coils(we just bring the second nearer to the first), the current transfer will be very small as compared to first. So we use Core to link these two winding, because of this current loss is so small.

Construction:-

 It consists of following,

1.Primary coil

2.Secondary coil

3.Core

4.AC current source

Working:-

Whenever we supplies ac current to primary coil then due to changing nature of ac current there produces change in magnetic flux around this winding. And due to this changing current starts to flow through core and reached to the secondary winding and through this secondary winding goes to external circuit, When we need to change low voltage to high voltage then we have to increase the winding of secondary coil. This type of transformer is known as Step up Transformer. If we want to change the high voltage into low voltage, than we have to decrease the winding of secondary coil. This type of transformer is known as Step down Transformer.

Work

Definition:-

"Work is the product of force and the distance covered by a body due to force applied on it"

Explanation:-

In physics work is done on a body, when we apply some force on it and it covers some distance in the direction of force.

Work is not done until body is not covering some distance whether force is applied on it or not, body has to cover some distance in order to get work done. or work will not be done until force will not be apply on it whether it is covering some distance or not. so both things are necessary.

Example:-

1.When you try to push the box by applying force on it and box start to move in direction of force, then your are doing work.

2.When you try to push the wall then you apply force but wall doesn't move, so you are not working (According to physics).

Unit:-

The Sl unit of work is joule J

Formula:-

Work also have an formula to calculate it mathematically,

W=F.d.cosθ

As define work is the product of force and distance and the angle between them. 

Conditions:-

1.This cos shows that when force applied and distance covered is in same direction then angle will be 0, where cos(0)=1, hence work will be maximum.

2. When force applied and distance cover will be perpendicular to each other than angle will be 90 and cos(90)=0, hence work will be 0.

3. When force applied and distance covered is in opposite direction  then work will be negative as, angle will be 180 and cos(180)=  -1.

AC Generator

Definition:-

"The machine which is used to convert mechanical energy into electrical energy(AC current) is known as AC Generator"

Explanation:-

The device which gives us AC current(Electrical energy) by taking mechanical energy from any source(could be us) is known as Ac generator. Its construction is similar to dc generator and its working is also same almost. 

The above shown diagram is of AC generator. our need is to get the current which changes its direction after every half cycle, so to get this we need to get the current from one slip ring for one half and for other slip ring for the second half. Slip rings are connected at different ends of closed circuit. where load is connected. So that load will get Ac current.

Construction:-

It consists of following parts:-

1.Magnet

2.Slip Rings or Commutator

3.Conducting Coil or Armature

4.Carbon brushes

5. Load  

Working:-

According to the Faraday's Law of electromagnetic induction, whenever a conducting coil is move or rotates across magnetic field emf produces in it and due to this, current starts to flow through it. So in this generator when coil will move by some mechanical force across magnetic field of magnet, then there will produce an EMF and because of this, current will start to flow through it(if coil path is closed or connected to other circuit). Direction of current will be according to Fleming's right hand rule. 

As shown in this diagram, For first half rotation of coil the current will go to the load form one slip ring and for 2nd half rotation of coil the current will go from the other slip rings to the load so it is giving ac current to the load as it is changing its direction after every half cycle.

Generator(DC)

Definition:-

"The device which converts mechanical energy into electrical energy is known as Generator."

Explanation:-

Generator use to produce electrical energy from mechanical energy for our purpose.

Above shown diagram is of DC generator, its construction is same as Electric motor(DC), the difference is that from where we give input in input, from there we get output from generator. the mechanical energy could of any type. for example moving pivot with your hand and by some other source.

Construction:-

It consists of:-

1.Magnet

2.Conducting Coil loop

3.Commutator

4.Carbon brushes

5.Battery

Working:-

According to Faraday's law, whenever a conducting coil will move across magnetic field then there will produce an EMF, and due to this, current will start to flow through coil (if path is closed). the direction of current will be according to Fleming's Right hand rule(Described below). Then this current will go through commutator and through carbon brushes it will go through battery and will charge. That its simple working!

Faraday's Law of electromagnetic induction:-

This law state's that" whenever a conducting coil is move across the magnetic field of magnet, then EMF will produce in coil and current will start to flow through it" Current direction would be according to Fleming right hand rule.

Fleming's Right hand rule:-

According to this law "Straighten your thumb, fore finger and middle finger so that they become perpendicular to each other(right angle to each other) and then your thumb will represent the coil, your fore finger will represent the magnetic field and your middle finger will represent the direction of current flow."

Electric Motor(AC)

Definition:-

"An electric device that converts an AC electric source into mechanical energy is known as AC electric motor"

The device that converts Electrical energy into mechanical energy for our use, we called that device electric motor.

Explanation:-

The above diagram is of ac motor that converts an ac source into mechanical energy. The problem we face in ac motor is that, ac current changes its direction after half cycle. So it is not possible for conducting coil to move in one direction for complete cycle of  ac current. To overcome this problem, we use split rings instead of commutator, so that we could reverse the direction of current. and coil could move in one direction.

Construction:-

It consists of,

1.Magnet

2.Conducting loop

3.Split rings

4.Carbon brushes

5.Ac source

Working:-

AC motor works on the same principle, as DC motor works. When we connect ac current source to the carbon brushes then through split rings current starts to flow through the wire( or conducting loop) so because there is also magnet field through wire and now current flowing through it, So according to Fleming's left hand rule, the coil will start to move. When ac current will change its direction split rings will change their direction and so coil will get same directed current and coil will move in one direction.

Electrical Motor(DC)

Definition:

"Electric motor is a device that converts electrical energy to mechanical energy"
The device which converts electrical energy into other form of energy which is mechanical energy so that we can take benefit from it.

Types of Motor:

There are two basic types of electric motor:-

1.DC motor

2.AC motor

 

DC motor Explanation:

The motor which converts DC power to the mechanical energy or power is known as dc motor.

Above diagram is of dc motor. It consists of a magnet, armature or conducting loops, carbon brushes, commutator, dc source or battery.

Working:-

When we connect the battery with the carbon brushes than through commutator they cause the current to flow through loops, as on the other hand there is also magnetic field from north to south so as we have studied Fleming's left hand rule(will explain below), the loops will move upward from one side and will move downward from other side. When this current carrying conductor(conducting loops) will change position at 90 degree than again according to the Fleming's rule this loop will move as it is going. So that how it works. other end of loop would be connected with the object to whom we want to provide mechanical energy. 

Fleming's Left hand rule:-

This rule states that" hold your left hand and tied your 1st finger, 2nd finger and thumb in such a way that they each other become perpendicular(Right angle) to each other. now if first finger is the direction of magnetic field and 2nd finger represent the current flowing through coil, then thumb will represent the force acting on it." 

Centripetal force

Definition:

"Centripetal force is a force, which keeps a body moving in a circular path and that force acting towards the center of that circular path."

Explanation:

A body never automatically or itself moves in a circular path it, there is always a reason or some force that causes it to move in a circular path and that force in general is known as a centripetal force. and that force is always directed towards  center. it means force is from the center of circular path that causes it to move in a circular path.

Example:

You tries to move a string in a circular path. one end of it is in your hand and other is tied with a stone. and consider that stone is a body. you provide force from your hand which is at the center of circular path in which stone(body) is moving.

Formula:

 

This equation shows that force depends on the mass of body and the velocity by which it is moving in path and the distance(r) between the center of circular path and body.