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When it comes to characterizing the electrical environment of a system, an electric field is an elegant way to do it. The electric field at any point in space around a system of charges will represent the force a unit positive test charge would experience if placed at that point. Here, we will discuss the physical significance of the electric field along with a few important questions.
Let us do a small activity. Take a comb, rub it through your hair. Now take few small pieces of paper and take the comb near to the pieces of paper. What did you notice? The pieces of paper stick to the comb. How are the pieces of paper sticking on the comb? This happens because of Electrostatic force. When you rub the comb through your hair, the comb gets charged. The comb can be either positively or negatively charged. Let's suppose it is negatively charged. The negatively charged comb, when brought closer to the paper induces an opposite charge i.e. A positive charge in the pieces of paper. We know that opposite charges attract. Hence, the positively charged comb attracts the negatively charged paper.
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KeyTerms: Electric Field, Electrostatic force, Comb, Static Condition, Electromagnetic Non-static Condition, Force, Volt, Unit of measurement, Coulomb's Law
What is Electric Field?
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An electrically charged particle is surrounded by a physical field, known as an Electric field. The electric field around the charged particle exerts a force on all the other charged particles nearby, the force can be either attracting or repelling. The Electric field is generally denoted by 'E'. The electric field is a vector quantity and the unit of measurement is Volt per Meter, also represented as 'V/m'.
The electric field at any point in space is equal to the force per unit charge experienced by a positive charge held at that point. This is the basic principle behind Coulomb's Law.
Also Read:
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| Electroscope | Gauss's Law | Dipole in a Uniform External Field |
| Electrical Insulators | Force multiple charges | Surface charge density formula |
Coulomb's Law
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According to Coulomb's law, the magnitude of the electric or electrostatic force between two point charges is:
- Directly proportional to the product of the magnitude of both the point charges
F ∝ |q1q2|
where q1, q2 is the magnitude of the point charges
- Inversely proportional to the square of the distance between the point charges
F ∝ 1 / d2
where d is the distance between the point charges
Now, on combining both the conditions:
F ∝ |q1q2| / d2
Remove the proportionality symbol and adding constant k, also known as Coulomb's constant.
Coulomb's law, the magnitude of the point charges, and the distance between them can be easily determined using Coulomb's law.
Read More: Electric Charges and Fields NCERT Solutions
Physical Significance of Electric Field
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Electric Field under Static Condition
Static means 'at rest'. The charged bodies, under the static condition, experience an electric field surrounding them. The electric field is defined at every point and changes from point to point.
Electric Field under Electromagnetic Non-static Condition
This is the condition where the accelerated motion of the charge gives rise to electromagnetic waves and this propagates with a speed c passing on a force on another charge. Time-dependent magnetic and electric fields are connected with the transport of energy.
Let take two charges q1 and q2, moving in an accelerated motion and has some amount of force between them. Suppose the charges are moving with the greatest speed that is the speed of light, c. The effect of this motion of charge q1 and q2 cannot arise instantaneously. A time delay can be observed between the effect (force on q2 charge) and cause (motion of q1 charge). The concept of the electric field is obvious and extremely useful in this context.
Electromagnetic waves are produced due to the accelerated motion of charge q1. The electromagnetic waves travel with the speed c towards charge q2 and exert a force on charge q2. The time delay is easily explained by the concept of field.
Despite the fact that electric and magnetic fields can only be observed by their effects (forces) on charges, they are considered physical entities rather than mathematical abstractions. They have their own dynamics, i.e., they evolve according to their own set of laws. They are also capable of transporting energy. Thus, a source of time-dependent electromagnetic fields that are turned on for a short period and then turned off leaves propagating electromagnetic fields carrying energy. Faraday was the first to develop the notion of field, and it is one of the most important concepts in physics.
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Previous Year Questions
- Charge density of long wire λ… [ BITSAT 2009]
- In the given circuit, what will be the equivalent resistance between the points AA and BB ? [ JIPMER 2006]
- How to adjust a system of three identical capacitors to get high electrostatic energy….. [ UPSEE2016]
- The number of excess electrons on the drop is… [VITEEE 2011]
- The kinetic energy attained by the particle after moving a distance y is…. [KEAM]
- A hollow metal sphere of radius RR is uniformly charged. The electric field due to the sphere... [NEET 2019]
Things to Remember
- Electric Field is a physical field surrounding an electrically charged particle. The electric field around the charged particle exerts a force on all the other charged particles nearby, the force can be either attracting or repelling.
- The electric field is a vector quantity and the unit of measurement is Volt per Meter, also represented as 'V/m'.
- Coulomb's law states that the magnitude of the electric or electrostatic force between two point charges is
- Directly proportional to the product of the magnitude of both the point charges
- Inversely proportional to the square of the distance between the point charges
- The magnitude of the point charges and the distance between them can be easily determined using Coulomb's law.
- The charged bodies, under the static condition, experience an electric field surrounding them. The electric field is defined at every point and changes from point to point.
- Under the electromagnetic non-static conditions, the accelerated motion of the charge gives rise to electromagnetic waves and this propagates with a speed c passing on a force on another charge.
Also Read: Dipole in a Uniform External Field
Sample Questions
Ques. What is Electric Field? (2 marks)
Ans. Electric Field is a physical field surrounding an electrically charged particle. The electric field around the charged particle exerts a force on all the other charged particles nearby, the force can be either attracting or repelling. The Electric field is generally denoted by 'E'. The electric field is a vector quantity and the unit of measurement is Volt per Meter, also represented as 'V/m'.
Ques. Explain the importance of the Electric Field? (2 marks)
Ans. The electric field helps in understanding the generation and flow of electricity. We've seen how electric fields represent the pulling or pushing force in a space between charges.
Ques. Explain the Physical significance of the electric field under static conditions? (2 marks)
Ans. The charged bodies, under the static condition, experience an electric field surrounding them. The electric field is defined at every point and changes from point to point.
Ques. Explain the Physical significance of Electric field under electromagnetic non-static conditions? (3 marks)
Ans. Two charges q1 and q2, moving in an accelerated motion and has some amount of force between them. Suppose the charges are moving with the greatest speed that is the speed of light, c. The effect of this motion of charge q1 and q2 cannot arise instantaneously. A time delay can be observed between the effect (force on q2 charge) and cause (motion of q1 charge). The concept of the electric field is obvious and extremely useful in this context.
Electromagnetic waves are produced due to the accelerated motion of charge q1. The electromagnetic waves travel with the speed c towards charge q2 and exert a force on charge q2. The time delay is easily explained by the concept of field.
Ques. Is the Electric field real? (1 mark)
Ans. Electric fields, have a genuine physical existence and are not simply theoretical constructions.
Ques: Write a brief description of the electric field. (2 marks)
Ans: The electric field is at each point in space. This is because the force per unit charge that a vanishingly small positive test charge will experience will be held at that point. The vector fields of this form are at times considered as force fields. This is the basis for Coulomb's law which states that the electric field varies with the source charge for stationary charges and is inverse with the square of the distance from the source. This means that if the source of the charge was doubled then the electric field would double. And after doubling we will perceive that if we move twice as far away from the source of the field at that point would be only one-quarter its original strength.
Ques: What is meant by Columb’s law? (4 marks)
Ans: According to Coulomb's law, the magnitude of the electric or electrostatic force between two point charges is:
- Directly proportional to the product of the magnitude of both the point charges
F ∝ |q1q2|
where q1, q2 is the magnitude of the point charges
- Inversely proportional to the square of the distance between the point charges
F ∝ 1 / d2
where d is the distance between the point charges
Now, on combining both the conditions:
F ∝ |q1q2| / d2
Remove the proportionality symbol and adding constant k, also known as Coulomb's constant.
Coulomb's law, the magnitude of the point charges, and the distance between them can be easily determined using Coulomb's law.
Ques: Why must the electrostatic field be normal to the surface at every point of a charged conductor? (Delhi 2012)
Ans: The electrostatic field must be normal to the surface at every point of a charged conductor so that the tangent on charged conductor gives the direction of the electric field at that particular point.
Ques: Why the electrostatic field lines do not form closed loops? (All India 2014)
Ans: Electric field lines do not form closed loops as the direction of an electric field is from positive to negative charge. Therefore, one can consider a line of force starting from a positive charge and ending on a negative charge. This shows that an electric field. lines do not form closed loops.
Ques: Plot a graph showing the variation of coulomb force (F) versus (1/r2) where r is the distance between the two charges of each pair of charges: (1µC, 2µC) and (2µC, – 3µC). Explain the graphs obtained. (All India 2010)
Ans:
Here positive slope implies that force is repulsive in nature and the negative slope shows that the force is attractive in nature.
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