Q4. Assertion: a magnetic field exists between the plates of a capacitor while it is being charged. Reason: the changing electric field between the plates is a displacement current, which produces a magnetic field just as a conduction current does. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion: the field approaches the same edge value just inside and outside the plate radius in the ideal symmetric model (NCERT page 204).
Q5. The electric flux between the plates of a capacitor changes at 4.0 × 1010 V m/s. Find the displacement current.
id = ε0 dΦE/dt = 8.85 × 10−12 × 4.0 × 1010 ≈ 0.35 A (NCERT Eq. (8.4), page 203).
Q6. A capacitor with plates of area 0.020 m2 is charged by a current of 1.5 A. At what rate does the electric field between the plates grow?
E = Q/(Aε0), so dE/dt = i/(Aε0) = 1.5/(0.020 × 8.85 × 10−12) ≈ 8.5 × 1012 V/(m s) (NCERT Eqs. (8.3)–(8.4), page 203).
Q7. A capacitor joined to a battery has charged fully. What is the displacement current between its plates now?
Zero. The charge, and with it the electric field between the plates, no longer changes, so ε0 dΦE/dt = 0 (reasoned from NCERT Eq. (8.4), page 203).