Electric Charges and Fields

Electric Charge is that physical property of matter due to which the other matter experience a force when matters are placed in electromagnetic field. Electric charge is also known as Charge, Electrical Charge and Electrostatic Charge. It is denoted by symbol ‘q’. It is a scalar quantity as charge has only magnitude and no direction.

The two types of charges exist in nature: Positive and Negative Charge.

Same charge repels each other and opposite charge attract each other. In the figure given below, we can see that like charge are repelling each other, while opposites are attracting each other. 



We know that in a nucleus proton and neutron exists while electron revolve around the nucleus. Proton (p+) have positive charge and electron (e-) have negative charge. As symbol of proton is (p+) so proton carrying positive charge and symbol of electron is (e-) so electron carrying negative charge. As number of proton and electron in a nucleus are equal so net charge on nucleus is zero.

For existing the net charge on a body the sum of positive and negative charge should be equal to zero.

Properties of Electric Charge





Charge is measured in terms of Coulombs (C)


Charge is a scalar quantity


Charge can be positive or negative


Charge of proton and electron have same in magnitude but opposite in sign. Proton have charge 1.6 * 10-19 C while electron have -1.6 * 10-19 C


Charge is conserved while transferring.


Charge is quantized in nature.







Electric Field




It is the region around a charge particle or object due to which another charge particle or object experience force. Electric Field is a vector quantity so we must consider the sign in numerical.



Formula of Electric Field

 

Unit of electric field: E = N/C



As, unit of force is Newton (N)  and charge is Coulomb ( C),  So unit of electric field is N/C.

Note: While writing the unit 1st letter should be capital.

In the above formula F is the force and q is the charge. F is calculated in terms of coulombs law.

Coulombs law is stated as force acting on a charge particle due to another charge particle is directly proportional to product of their charges and inversely proportional to square of distance between the charges.

From the above definition, of coulomb’s force

  

Where, k is the proportionality constant and its value is 9 * 109 Nm2/C2. It is different for different medium.

SI unit of F is = N m2 C2/C2 m2

So, on solving above equation we get F = Newton (N)






How to calculate SI Unit of any Physical Quantity?



Quality

SI unit


Charge

Coulomb (C)


Mass

Kilogram (Kg)


Distance

Meter


Force

Newton (N)




These four quantities are the basic quantities with the help of these quantities we can find the SI unit of any other physical quantity.



SI unit of Electric Field

We, know that formula of E is = F/q

So, SI unit of F is Newton and Charge is Coulomb.

E = N/C



How to calculate the Direction of E?

Direction of Electric Field is always from positive charge to negative charge. In terms of single positive charge Electric field move away from the positive charge as shown in the first part of the diagram and in terms of negative charge Electric field move towards the negative charge as shown in the second part of the diagram.

   

In the above diagram, we can see that in terms of positive charge E is moving away from positive charge Similarly in terms of negative charge E moving away from negative charge.
 

Diagram of E in terms of two Charges



In this diagram, all the three directions are used. Firstly, Electric field goes from Positive charge to negative charge. Secondly, In terms of positive charge field lines are moving away from positive charge and in terms of negative charge field lines are coming towards the charge.

Frequently Asked Questions (FAQs)



Q1. Two insulated charge sphere A and B of identical size having charges qA and -3qA respectively. When they are brought in contact with each other and then separated what are the new charges on them?

Sol. As two charges are of opposite sign, they will attract each other so there will be the simple addition of charge.

       New charge on them is  Q = (qA) + (-3qA / 2)

     Q = -qA
 

Q2.  What is the basic condition for existing the net charge on a body?

Sol. The basic condition for existing the net charge on a body is that number of positive and negative charge should not be equal to zero.
 

Q3. What is the Charge on Electron?

Sol.  Charge on electron is -1.6 *10-19 C.
 

Q4.  Is the force acting between two point charges q1 and q2 kept at some distance apart, attracting or repulsive (a) q1 q2 > 0 (b) ) q1 q2 < 0 ?

Sol.  

(a) If q1 q2 > 0 then the force is repulsive because if both the charges are positive and negative (same charges) only then their product is greater than zero. We know that same charges always repel each other.

(b) If q1 q2 < 0 then the force is attractive because one charge will be positive and other will be negative and opposite charge attract each other.



Q5. What is the SI unit of Electric Field?

Sol. SI unit of electric field is N/C.



Q6. What is the Dimensional Formula of Electric Field?

Sol. The dimensional formula of electric field is [MLT-2C-1].



Q7. If two charges having equal magnitude are separated by unit distance and exert a force of 15 N on each other. What will be the force exerted by the same charges kept at same distance but the charges are placed in water?

Sol.    

F1 = 15 N, r1 = 1 meter, k air = 1 , q1 = q2 = q

F2 = 15 N, r2 = 1 meter, k water = 80

F1 = k air q1 q2 / r2,      F2 = k water q1 q2 / r2

F2 = k water q1 q2 / r2

F2 = 80 * q2/ 1

F2 = 80 q2 N.



Q8. Two spheres of radius r1 and r2 are connected by a wire. What will be the ratio of their electric field?

Sol.  We know that F= k q1 q2/r2 and E = F/q.

        So, E1/E2 = r22/r12.




What is Electric Charge?

Electric Charge is a physical property of matter due to which a matter experience a force on another charge matter when placed in electromagnetic field (electric or magnetic field).
 

Another Definition of Electric Charge

According to Franklin electric charge is used for electrostatic interaction. For Example: A body can interact with another body only if charge is present in that body.
 

What is the definition of charge in daily life?

In daily life we use the term charge many times. For Example: charging a phone. We can charge an object when we apply voltage to it.

Q= CV

Q  = Charge, C = Capacitance, V= Voltage.
 

How Charge Originate?

It was assumed that origin of charge start from atomic structure. Let us consider a atom having size 10 -10 meter. Inside the atom nucleus in present and size of nucleus is 10 -15 meter. Electrons revolve around the nucleus. As we know that symbol of proton is (P + ) so charge on proton is + and symbol of electron is (e – ) and charge on electron is – so from sign convention we can tell that the object is positively charged or negatively.



In the above figure we can see that how charge originate from the atomic structure. From the atom electrons and protons originate.
 

What is SI unit of Charge?

SI unit of charge is Coulomb (C).
 

What is Elementary Charge?

Elementary Charge is the magnitude of charge carried by single electron or proton. The charge on electron is negative and it is denoted by (-e) while the charge on proton is positive and it is denoted by (+e).

The charge on single proton is (+ 1.6 * 10 -19 C ) while the charge on single electron is (- 1.6 * 10 -19 C).

How many types of charge exist in nature?

There are two types of charge exists in nature:

Positive Charge
Negative Charge


“Same charge repel each other and opposite charge attract each other”

In the diagram given below we can see that same charge repel each other and opposite charge attract each other.



Note : In case of neutral charge number of positive charge is equal to the number of negative charge but neutral charge is not considered the type of charge. There are only two types of charge exist. For Example: Positive and Negative.



What are the Properties of Electric Charge?


Electric Charge is conserved, it can neither be created nor be destroyed in an isolated system.


The SI unit of charge is Coulomb (C).


The object becomes positively charge if it gives some charge to another object.


The object which accept the charge from another body become Negatively Charged.


Charge is quantized in nature.
 



How Electrons Come out from the Neutral Object?

Let us consider a neutral object (equal number of proton and electron). In neutral object each electron is attracted to each proton (because number of positive charge is equal to number of negative charge). The force we are applying  to pull electrons from the object is equal to the force which is pulling  back electrons to the charged object because amount of positive  charge is equal to the negative charge, so both forces cancel out with each other. So we have to do some external work to pull the electrons from the object.

 There are various method to pull the electrons from the surface.


How electrons can pull from the object with the help of battery: Battery consist  two terminals positive and negative. On applying the external voltage electrons are attracted towards the positive terminal and electron can pull out of the object.


Another way to pull electron is hit an object with high energy so that electrons come out from the object, that energy is more than the energy which are pulling electrons back to the metal surface.
 



How can we charge an object?

There are three methods to charge an object:


Charge by induction method


Charge by conduction method


Charge by friction method
 



How Electric Field can generate from Charge?

Electric Field  Generate when charge is in rest while the moving charge produce magnetic field.



In case of positive charge direction of electric field is away from the charge while in case of negative charge direction of electric field is towards the charge as shown in the figure.
 

What is Current?

Current may be defined as charge flowing through a closed circuit per unit time.
 

Another Definition of Electric Current

A current is said to be one Ampere if charge of one Coulomb flows  through a point in one Second.

I = q/t

Image of Electric Current in daily life



In above figure, current is flow in the circuit when we apply the voltage to the circuit the charge generates and electrons flows in the circuit. The direction of current is opposite to the direction of flow of electrons. 
 

What is Formula of Current?

I = q/t

Where,  I is the current flowing in the circuit

             q is the charge flowing in the circuit

              t is the time.
 

What is SI Unit of Current?

SI unit of current is Ampere.

What is Dimensional Formula of Current?

Dimensional formula of current is [ CS-1 ].
 

Frequently Asked Questions (FAQs)
 

Q1. What is the definition of charge?

Sol. A charge is said to be one coulomb if one Ampere current flows in a circuit in one second.
 

Q2. What are positive and negative charge?

Sol.  A neutral atom becomes an ion if it loose or gain electron or proton. As we know that neutral atom don’t have any charge it becomes positive charge if it loose electron and it becomes negative charge if it gain electron.
 

Q3. What is the unit for measurement of charge?

Sol. The unit for measurement of charge is coulomb.
 

Q4. What is an electric current?

Sol. Electric current is the ratio of charge per unit time.
 

Q5. Why do two electrons repel each other?

Sol. Two electrons repel each other because both the electrons have same charge. For Example: Negative and we know that same charge repel each other.




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