Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Inside a uniformly polarised dielectric slab, any small volume element has no net charge, though it has a net dipole moment.
Reason (R): Inside the slab, the positive charge of one molecular dipole sits close to the negative charge of the next dipole.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are correct and (R) is the correct explanation of (A).
Assertion (A) Inside a uniformly polarised dielectric slab, any small volume element has no net charge, though it has a net dipole moment. — True. A small volume \( \Delta v \) still holds a very large number of molecular dipoles. Their dipole moments add up to \( P\,\Delta v \) along the field, but their charges add up to zero.
Reason (R) Inside the slab, the positive charge of one molecular dipole sits close to the negative charge of the next dipole. — True. In a uniform polarisation the dipoles line up end to end along the field. So the positive end of one dipole lies next to the negative end of the next one.
Why Reason (R) explains Assertion (A)?
Inside the slab, every positive end has a negative end next to it. Their charges balance, so no net charge is left in any small volume.
Only at the two faces normal to the field are the end charges left unbalanced. These give the induced surface charges \( \pm\sigma_p \).
NCERT (2026-27):
Dielectrics and Polarisation – “Anywhere inside the dielectric, the volume element Δv has no net charge (though it has net dipole moment). This is, because, the positive charge of one dipole sits close to the negative charge of the adjacent dipole.”