Magnetic force on a current element Idl in a magnetic field is
A Idl⋅B
B Idl×B
C B/I
D Zero
Lorentz force for current element.
Magnetic dipole moment of a current loop is
A IA
B NIA
C μ₀IA
D IB
For N turns, m = NIA.
Field at the axial point of a circular loop varies as
A 1/r
B 1/r²
C 1/r³
D Constant
Magnetic susceptibility χm of paramagnets is
A Large negative
B Small positive
C Large positive
D Zero
Ferromagnetic saturation occurs when
A Domains become random
B All domains align fully
C χ → 0
D Magnet loses magnetism
Inside a perfect diamagnet, magnetic field is
A Increased
B Unchanged
C Slightly decreased
D Expelled
Meissner-like behavior.
In EMI, the induced current always
A Opposes cause
B Aids cause
C Is random
D Does not depend on flux
Lenz’s law.
Lenz’s law ensures
A Charge conservation
B Energy conservation
C Momentum conservation
D Magnetic charge conservation
In a rotating coil generator, induced EMF is maximum when
A Coil plane ∥ field
B Coil plane ⟂ field
C Coil stops
D Magnetic field is zero
dΦ/dt maximum.
The back EMF of a motor is due to
A Electrical resistance
B Mechanical rotation cutting flux
C Inductor action
D Capacitive effect
A solenoid’s inductance increases when
A Core removed
B Air used
C Iron core inserted
D Number of turns decreases
The mutual inductance M12 equals M21 because
A Flux is constant
B Reciprocity theorem
C Turns equal
D Resistance equal
Induced EMF per turn in a transformer is proportional to
A Current
B Voltage
C Rate of change of flux
D Frequency only
Transformer equation is
A Vs/Vp = Np/Ns
B Vs/Vp = Ns/Np
C Vs = IR
D None
In AC circuits, the average power in pure inductance is
A Maximum
B Zero
C Negative
D Constant
Voltage and current 90° out of phase.
The RMS value of AC voltage is
A V0
B V0/√2
C 2V0
D Zero
A capacitor’s reactance decreases when
A Frequency decreases
B Frequency increases
C Capacitance decreases
D None
The impedance of a series LCR circuit at resonance is
A Zero
B Maximum
C Minimum = R
D Infinity
Quality factor Q indicates
A Energy stored per cycle
B Sharpness of resonance
C Resistance only
D Only inductance
Skin depth δ for conductors is
A Higher at high frequency
B Lower at high frequency
C Infinite
D Zero
EM waves arise when there is
A Constant charge
B Accelerating charge
C Static charge
D Uncharged matter
Displacement current density is
A σE
B ϵ ∂E/∂t
C μ ∂H/∂t
D ϵE
Maxwell corrected Ampere’s law to
A Include electric flux changes
B Include magnetic flux changes
C Allow monopoles
D Permit static fields only
EM wave speed decreases when
A μ and ε increase
B μ increases only
C ε decreases
D Frequency increases
The ratio E/B in free space equals
A μ₀
B ε₀
C c
D 1/c
Energy density in magnetic field is
A 1/2ϵE²
B 1/2μH²
C EH
D EB
Wave impedance Z = √(μ/ϵ) equals 377 Ω for
A Water
B Glass
C Vacuum
D Iron
Poynting vector gives
A Charge flow rate
B Power per unit area
C Resistance
D Capacitance
In plane EM waves, E, B, and propagation direction are
A Coplanar
B Perpendicular pairwise
C Parallel
D Same direction
For good conductors, wave attenuation constant is
A Zero
B Large
C Negative
D Constant
Anomalous dispersion corresponds to
A dn/dω > 0
B dn/dω < 0
C n constant
D n infinite
The group velocity of a dispersive medium is
A Equal to phase velocity
B May be less or greater than phase velocity
C Zero
D Infinite
Conductivity affects
A Penetration depth
B Wave attenuation
C EM heating
D All of these
EM waves in a perfect conductor
A Reflect completely
B Transmit fully
C Are amplified
D Are partially lost
Magnetic field inside a conductor carrying AC is
A Uniform
B Maximum at center
C Maximum at surface
D Zero everywhere
Skin effect.
Phase lag between current and voltage in RL circuit is
A 0°
B 90°
C Between 0° and 90°
D 180°
A capacitor causes voltage to
A Lead current
B Lag current
C Be in phase
D Double
EM waves satisfy
A Maxwell equations
B Schrodinger equation
C Einstein field equation
D Poisson equation
Maxwell’s equations predict
A Matter waves
B Gravitational waves
C EM waves
D Sound waves
The source of EM waves is
A Constant velocity charges
B Accelerating charges
C Stationary electrons
D Neutrons
Radiation pressure of EM waves is due to
A Mass
B Charge
C Momentum carried by waves
D Temperature
In free space, EM waves are
A Longitudinal
B Transverse
C Both longitudinal and transverse
D Standing
EM wave equation in free space is
A ∇²E = μ₀ϵ₀ ∂²E/∂t²
B ∇²E = 0
C ∇E = 0
D ∇×E = 0
Light intensity is proportional to
A E
B H
C E²
D EB
Magnetic permeability of a ferromagnet is
A Always μ₀
B Slightly > μ₀
C Much greater than μ₀
D Zero
In induction heating, high-frequency currents cause
A Greater penetration
B Stronger skin effect
C Lower temperature
D No heating
A sinusoidal varying E-field produces
A Static B-field
B Sinusoidal B-field
C No B-field
D Constant B-field
The direction of induced EMF is determined by
A Ampere’s law
B Gauss law
C Lenz’s law
D Maxwell’s law
EM waves can propagate in
A Vacuum only
B Conductors only
C Insulators only
D Vacuum and matter
The combined energy density of EM wave is
A εE²
B μH²
C 1/2(εE² + μH²)
D EH