Courses
Courses for Kids
Free study material
Offline Centres
More
Store Icon
Store
seo-qna
SearchIcon
banner

The unit of absolute permittivity is
A. Fm (Farad-meter)
B. Fm1 (Farad/meter)
C. Fm2 (Farad/meter2)
D. F (Farad)
E. None of these

Answer
VerifiedVerified
486.6k+ views
like imagedislike image
Hint: As a first step, you could recall Coulomb’s law for electrostatic force. Now, as the options are in terms of SI unit of capacitance (Farad), we could recall its expression in terms of charge Q and potential difference V. Then, you could substitute V in terms of work done and Q and thus we will get an expression for Q2 which can be substituted in ohm’s law and then by substituting the respective units for each of them you will get the unit of absolute permittivity.

Formula used:
Coulomb’s law,
F=14πε0Q2r2
Expression for capacitance,
C=QV

Complete answer:
In the question, we are asked to find the unit of absolute permittivity from the given options.
In order to answer this, let us recall the expression for force given by Coulomb’s law. So, by coulomb’s law we have,
F=14πε0Q2r2
Where, F is the force between two charges Q kept at a distance of r between them and ε0 is the absolute permittivity or the permittivity of the free space or vacuum. Rearranging the above expression we get,
ε0=Q24πr2F ……………………………………. (1)
Since the given options contain Farad in it, let us recall the expression for capacitance of which Farad is the SI unit. So, capacitance by definition is given by,
C=QV ……………………………………. (2)
Where, V is the potential difference across the capacitance and we know that V by definition is given by,
V=WQ
Now (2) could be given by,
C=Q2W
Q2=CW ………………………………………….. (3)
Substituting (3) in (1), we get,
ε0=CW4πr2F……………………………………. (4)
We know that work done by definition is the product of force and displacement and hence Newton-metre(Nm) will be its SI unit.
Now, we could substitute the respective SI units for all the quantities in (4) to get,
ε0=F×Nmm2×N
ε0=Fm1
Therefore, the SI unit of absolute permittivity is found to be Farad per meter(Fm1).

Hence, option B is found to be the right answer.

Note:
Absolute permittivity could be defined as the measure of the electric polarizability of a dielectric. When we use the term ‘permittivity’, we mean the relative permittivity which is a dimensionless quantity. It is defined as the ratio of permittivity of a medium to that of the permittivity of vacuum.
Latest Vedantu courses for you
Grade 8 | CBSE | SCHOOL | English
Vedantu 8 CBSE Pro Course - (2025-26)
calendar iconAcademic year 2025-26
language iconENGLISH
book iconUnlimited access till final school exam
tick
School Full course for CBSE students
EnglishEnglish
MathsMaths
ScienceScience
₹49,800 (9% Off)
₹45,300 per year
Select and buy