How to Measure the Unit of Electrical Field
Overview
Coulomb's law deals with the force that acts between two distinct electric charges. According to the fundamental concept of the electric field,
An electric charge modifies the space around it by producing an electric field.
When another charge is introduced in this electrically modified region, it will experience some force due to the electric field produced by the first charge.
Coulomb's law is applied to static charges. An electric field is produced due to the motion of charged particles, and also when charges move relative to each other. Based on the experiments, it has been found that the electric field propagates through space at a finite speed (speed of light). The electric field concept is an essential aspect of the propagation of an electromagnetic wave through space, in a manner analogous to the propagation of light. By understanding the concept of the electric field, we can get to know how starlight travels vast distances through empty space.
Coulomb's law is based on the idea of force acting at a distance. This force is caused by an electric field and acts upon a charge placed in this electric field. The electric field is the real concept and is denoted by the electric field lines. The electric field lines are useful in describing the motion of a charge in the electric field.
Definition of the electric field
The electric field \[\vec{E}\] is a vector quantity. It exists in almost every point of space. The electric field describes the force which acts on a particle that is placed in the field.
For an arbitrary charged particle having charge q, the electric field is given by
\[\vec{E} = \frac{\vec{F}}{q}\]
The dimension of the electric field is Newton's/coulomb or N/C.
Based on the electric field, the electric force is described as:
\[\vec{F} = q \vec{E} \]
For a positive charge q, the direction of the electric field is in the same direction of the force vector.
We can calculate the value of the electric field by using Coulomb's law. By substituting a test charge q in the numerator of Columbus law, and a charge qi, we can get the electric field as follows.
Coulomb's Law:
\[\vec{F} = \frac{1}{4\pi \epsilon _{0}}\frac{qq_{i}}{r^{2}}\widehat{r}_{i}\].
Electric Field:
\[\vec{E} = \frac{\vec{F}}{q} \frac{1}{4\pi \epsilon _{0}} \frac{q_{i}}{r^{2}} \hat{r_{i}}\]
Where \[\widehat{r}_{i}\] is the unit vector, which indicates the direction of the electric field between from the source charge to the target test charge i.e., from q to qi.
Unit of Electric Field
The SI unit of an electric field is volt/meter.
Explanation: Electric field intensity is the force that acts on a unit positive charge placed in that field. The electric potential is the amount of work that is required to bring a positive unit charge from infinity to the point of influence of the electric field.
From this explanation, we can say that, when a charged particle moves in a region of the electric field, an electric potential is developed. Thus, the electric potential is the work done in moving a particle. We can calculate the electric potential by multiplying the electric field with a displacement vector. Electric potential is given by:
E ∗ r = v
Insights on electric field
The electric field is a modified electric force experienced by a unit positive test charge.
You can visualize the concept of the electric field in this way. Imagine a unit positive test charge placed at a point. Now bring a charge of higher magnitude near that test charge. The test charge will experience either a push or pull due to the influence of the electric field of the other charge.
The force that the test charge experiences at any point of the electric field, when divided by the magnitude of the test charge, is the electric field at that point. The direction in which the test charge experiences force is the direction of the electric field at that point. An electric field exists even if the test charge is removed from that point.
FAQs on Unit of Electric Field
1. What is the SI unit of electric field and how is it defined as per CBSE 2025–26 syllabus?
The SI unit of electric field is volt per meter (V/m). It is defined as the force experienced per unit positive charge at a point in space. In formula terms, Electric Field (E) = Force (F) / Charge (q), with the unit being newton per coulomb (N/C), which is equivalent to volt per meter (V/m).
2. Explain how Coulomb's law is used to calculate the electric field due to a point charge.
According to Coulomb's law, the electric field (E) produced by a point charge (q) at a distance (r) from it is given by:
- E = (1/4πε₀) × (q/r²)
3. How can electric field lines be used to visualize the strength and direction of an electric field?
Electric field lines represent the direction and strength of the electric field.
- They originate from positive charges and end at negative charges.
- The closer the lines, the stronger the field.
- The tangent to a field line at any point gives the direction of the electric field at that point.
4. What is the relationship between electric field and electric potential?
The electric field is related to the change in electric potential over distance. Mathematically, E = -dV/dr, where V is electric potential and r is displacement. This means the electric field points in the direction of the greatest decrease in potential.
5. Why is the electric field considered a vector quantity, and how does this affect its calculation?
The electric field is a vector because it has both magnitude and direction. When calculating the net electric field from multiple sources, vector addition must be used, accounting for both the size and direction of each field contribution.
6. If the unit positive charge is removed from its position in an electric field, does the field still exist?
Yes, the electric field exists in space regardless of whether a test charge is present or not. The presence of the source charge modifies the space around it to create an electric field, which can act on any charge that enters the region later.
7. What is the main difference between electric field and electric force?
The electric field is a property of the space around a charge, indicating the force that would act on a unit positive test charge placed there. Electric force refers to the actual force experienced by a charge placed in that field, calculated as F = q × E.
8. How can you experimentally determine the direction of an electric field at a point?
Place a small unit positive test charge at the point. The direction in which the charge experiences a force is the direction of the electric field at that location.
9. Describe a real-life example where understanding electric field is important.
Understanding the electric field is crucial in the design of electronic devices such as capacitors and in technologies like inkjet printers and photocopiers, where control of charged particles using electric fields is essential for proper functioning.
10. What misconceptions do students often have about the direction or existence of electric fields?
A common misconception is that the electric field exists only when a test charge is present, but in reality, it is created by the source charge alone. Another misconception is that the direction of electric field lines can form closed loops; in fact, they always begin on positive and end on negative charges or infinity.
