Question

Consider the two idealised systems

(i) a parallel plate capacitor with large plates and small separation and

(ii) a long solenoid of length L >>R, radius of cross-section. In (i) $\overrightarrow { \mathrm { E } }$ is ideally treated as a constant between plates and zero outside. In (ii) magnetic field is constant inside the solenoid and zero outside. These idealised assumptions, however, contradict fundamental laws as below

• A. Case (i) contradicts Gauss’s law for electrostatic fields.
• B. Case (ii) contradicts Gauss’s law for magnetic fields.
• C. Case (i) agrees with .
• D. Case (ii) contradicts = Ien.

Answer 1

Answer: (B)

Case (ii) contradicts Gauss’s law for magnetic fields.

Answer 2

According to Gauss’s law in magnetism $\oint \overrightarrow { \mathrm { B } } \cdot \overrightarrow { \mathrm { dS } } = 0$ which implies that number of magnetic field lines entering the Gaussian surface is equal to the number of magnetic field lines leaving it. Therefore case (ii) is not possible.