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## 309. The sequence for finding H from E is a) E-B-H b) E-V-H c) E-D-H d) E-A-H

Answer: a Explanation: From E, we can compute B using the Maxwell first law. Using B, the parameter H can be found since B = μH. Thus the sequence is E-B-H is true.

Answer: a

See lessExplanation: From E, we can compute B using the Maxwell first law. Using B, the

parameter H can be found since B = μH. Thus the sequence is E-B-H is true.

## 308. The Gauss law for magnetic field is valid in a) Air b) Conductor c) Dielectric d) All cases

Answer: d Explanation: The Gauss law for magnetic field states that the divergence of B is always zero. This is valid for all cases like free space, dielectric medium etc.

Answer: d

See lessExplanation: The Gauss law for magnetic field states that the divergence of B is always

zero. This is valid for all cases like free space, dielectric medium etc.

## 307. Find the sequence to find B when E is given. a) E-D-H-B b) B-E-D c) H-B-E-D d) V-E-B

Answer: a Explanation: From E, D can be computed as D = εE. Using the Ampere law, H can be computed from D. Finally, B can be calculated from H by B = μH.

Answer: a

See lessExplanation: From E, D can be computed as D = εE. Using the Ampere law, H can be

computed from D. Finally, B can be calculated from H by B = μH.

## 306. Which equation will be true, if the medium is considered to be air? a) Curl(H) = 0 b) Div(H) = 0 c) Grad(H) = 0 d) Div(H) = 1

Answer: b Explanation: From the Gauss law for magnetic field, the divergence of the magnetic flux density is zero. Also B = μH. Thus divergence of H is also zero, i.e, Div(H) = 0 is true.

Answer: b

See lessExplanation: From the Gauss law for magnetic field, the divergence of the magnetic flux

density is zero. Also B = μH. Thus divergence of H is also zero, i.e, Div(H) = 0 is true.

## 305. Which quantity is solenoidal in the electromagnetic theory? a) Electric field intensity b) Electric flux density c) Magnetic field intensity d) Magnetic flux density

Answer: d Explanation: The divergence of the magnetic flux density is zero. This is the Maxwell fourth equation. As the divergence is zero, the quantity will be solenoidal or divergent less.

Answer: d

See lessExplanation: The divergence of the magnetic flux density is zero. This is the Maxwell

fourth equation. As the divergence is zero, the quantity will be solenoidal or divergent

less.

## 304. The Gauss law employs which theorem for the calculation of charge density? a) Green theorem b) Stokes theorem c) Gauss theorem d) Maxwell equation

Answer: c Explanation: The Gauss divergence theorem is given by ∫ D.ds = ∫Div(D).dv. From the theorem value, we can compute the charge density. Thus Gauss law employs the Gauss divergence theorem.

Answer: c

See lessExplanation: The Gauss divergence theorem is given by ∫ D.ds = ∫Div(D).dv. From the

theorem value, we can compute the charge density. Thus Gauss law employs the Gauss

divergence theorem.

## 302. The charge density of a system with the position vector as electric flux density is a) 0 b) 1 c) 2 d) 3

Answer: d Explanation: The divergence of the electric flux density is the charge density. For a position vector xi + yj + zk, the divergence will be 1 + 1 + 1 = 3. Thus by Gauss law, the charge density is also 3

Answer: d

See lessExplanation: The divergence of the electric flux density is the charge density. For a

position vector xi + yj + zk, the divergence will be 1 + 1 + 1 = 3. Thus by Gauss law, the

charge density is also 3

## From the Gauss law for electric field, we can compute which of the following parameters? a) B b) H c) E d) A

Answer: c Explanation: From the Gauss law for electric field, we can find the electric flux density directly. On substituting, D= ε E, the electric field intensity can be calculated.

Answer: c

See lessExplanation: From the Gauss law for electric field, we can find the electric flux density

directly. On substituting, D= ε E, the electric field intensity can be calculated.

## 330. The gradient of the magnetic vector potential can be expressed as a) –με dV/dt b) +με dE/dt c) –με dA/dt d) +με dB/dt

Answer: a Explanation: The gradient of A is the ratio of the negative gradient of electric potential to the speed of light c. We can write c = 1/√(με). Thus grad(A) = -με dV/dt is the required expression.

Answer: a

See lessExplanation: The gradient of A is the ratio of the negative gradient of electric potential to

the speed of light c. We can write c = 1/√(με). Thus grad(A) = -με dV/dt is the required

expression.

## 329. When electric potential is null, then the electric field intensity will be a) 0 b) 1 c) dA/dt d) –dA/dt

Answer: d Explanation: The electric field intensity is given by E = -Grad(V)- dA/dt, where V is the electric potential and A is the magnetic vector potential. When V is zero, then E = -dA/dt.

Answer: d

See lessExplanation: The electric field intensity is given by E = -Grad(V)- dA/dt, where V is the

electric potential and A is the magnetic vector potential. When V is zero, then E = -dA/dt.