Chapter 8: Magnetism, EMI, Maxwell’s Equations & EM Waves (Set-2)

A current element produces a magnetic field whose magnitude is given by

A Ampere’s law

B Biot–Savart law

C Faraday’s law

D Maxwell–Ampere law

Magnetic field inside a long solenoid is

A Zero

B Non-uniform

C Nearly uniform

D Inversely proportional to current

Magnetic field in a toroid depends on

A Radial distance from center

B Height of toroid

C Flux only

D None

Magnetic dipole moment of a current loop is proportional to

A Current

B Loop area

C Both A and B

D Only number of turns

Force on a moving charge in a magnetic field is zero if

A Charge is zero

B Velocity ∥ B

C B = 0

D All of these

Cyclotron frequency depends on

A Mass & charge of particle

B Magnetic field

C Radius of orbit

D Both A and B

The Hall effect is used to measure

A Resistivity

B Carrier density

C Permeability

D Flux

Hall voltage increases when

A Magnetic field decreases

B Charge density increases

C Current increases

D Sample thickness increases

A positive Hall coefficient implies

A Electrons

B Holes

C No carriers

D Both electrons and holes equally

Hall coefficient dimensions are

A m³/C

B m²/C

C m/C

D None

Diamagnetic materials are repelled because

A Permanent dipoles form

B Induced dipoles oppose magnetic field

C Electrons align parallel

D Strong exchange interactions exist

Paramagnetic susceptibility is

A Negative

B Weak positive

C Strong positive

D Zero

Ferromagnetic domains are

A Random atomic groups

B Regions with aligned dipoles

C Temporary structures

D Only found in liquids

Coercivity of a ferromagnet indicates

A Magnetic induction

B Heat capacity

C Resistance to demagnetization

D Energy stored

A material with small hysteresis loss is suitable for

A Permanent magnets

B Transformer cores

C Hard disks

D Magnetic memory

Faraday’s law in integral form is

A ∮E⋅dℓ=0

B ∮E⋅dℓ=−dΦB/dt

C ∮B⋅dℓ=μ0I

D ∇⋅E=ρ/ϵ0

Induced EMF in a straight conductor moving perpendicularly in a magnetic field is

A BL

B BIL

C BvL

D v/L

EMF induced in a coil is zero when

A Flux is constant

B Flux changes

C Coil rotates

D Magnetic field is strong

Lenz’s law determines

A Magnitude of EMF

B Direction of induced EMF

C Phase of voltage

D Inductance

Mutual inductance M is

A Always positive

B Always negative

C Zero for any two coils

D Dependent on angle between coils

The energy stored in an inductor is

A 1/2 CV²

B 1/2 LI²

C 1/2 RI²

D L²I

The time constant of an RL circuit is

A R/L

B L/R

C LR

D 1/LR

Eddy currents are produced due to

A Changing electric field

B Changing magnetic flux

C Constant magnetic field

D Charge flow in vacuum

Eddy current losses can be reduced by

A Laminating cores

B Increasing thickness

C Increasing flux

D Using pure iron

In AC circuits, inductive reactance increases with

A Decreasing frequency

B Increasing frequency

C Inductance decreasing

D None

RMS value of AC current is

A Peak value

B Zero

C I0/2

D 2I0

Power factor in AC circuits is

A sin φ

B cos φ

C tan φ

D φ itself

A capacitor in AC causes

A Current to lag voltage

B Voltage to lag current

C No phase difference

D Both to vanish

Resonance in LCR circuit occurs when

A XL = XC

B XL = R

C XC = R

D R = 0

At resonance, the impedance is

A Maximum

B Minimum

C Zero

D Infinite

Maxwell’s displacement current accounts for

A Magnetic monopoles

B Continuity of current

C Electric field in conductors

D Light propagation only

The modified Ampere–Maxwell law is

A ∇⋅B = 0

B ∇×B = μ0J + μ0ϵ0∂E/∂t

C ∇×E = −∂B/∂t

D F = q(E + v×B)

A consequence of Maxwell’s equations is

A Existence of instantaneous action-at-distance

B Existence of EM waves

C Inability of waves to propagate in vacuum

D B-field only

EM waves are generated by

A Constant electric field

B Constant magnetic field

C Accelerating charges

D Stationary charges

In EM waves, ratio of E/B is

A c

B c²

C 1/c

D 0

Wave impedance in a medium is

A √(μ/ϵ)

B √(ϵ/μ)

C με

D 1/√(μϵ)

Poynting vector magnitude is

A EH

B EB

C E/H

D H/E

Electromagnetic energy density is

A 1/2(ϵE² + μH²)

B EHEH

C E²H

D ϵμEH

In conductors, attenuation of EM waves is proportional to

A Conductivity

B Resistivity

C Vacuum permittivity

D None

Skin depth decreases when

A Conductivity decreases

B Frequency decreases

C Permeability increases

D Resistivity increases

For good conductors, wave propagation is

A Efficient

B Poor due to absorption

C Constant velocity

D Impossible

Phase velocity in conductors is

A Greater than c

B Less than c

C Zero

D Unrelated to frequency

Dispersion occurs when

A Wave speed depends on frequency

B Wave speed constant

C Medium is vacuum

D No magnetic field

Normal dispersion implies

A dn/dω < 0

B dn/dω > 0

C n = constant

D n = 0

Conductivity σ affects

A Reflection coefficient

B Skin depth

C Attenuation

D All of these

In a dielectric, EM wave velocity is

A 1/√(μϵ)

B c

C Infinite

D Zero

Magnetic permeability of vacuum is

A 8.85×10⁻¹²

B 4π×10⁻⁷

C 377

D 1

Gauss’s law for magnetism implies

A Magnetic flux is zero

B Magnetic monopoles exist

C Divergence of B is zero

D B is always constant

In time-varying fields, curl E equals

A Zero

B Constant

C −∂B/∂t

D ∂E/∂t

EM wave equation for electric field is

A ∇⋅E = 0

B ∇²E = 0

C ∇²E = μϵ ∂²E/∂t²

D ∇×E = 0

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