Which expression gives the electric force on a stationary test charge q in field E?
A F = qE
B F = q/E
C F = E/q
D F = q+E
Answer: A. F = qE. The electric field is force per unit test charge.
What SI unit may express electric-field magnitude?
A N/C
B Wb
C A/m
D H/m
Answer: A. N/C. Electric field is force in newtons per coulomb of charge.
From an isolated positive point charge, how are electric-field lines directed?
A Radially inward
B In closed circles
C Along zero field
D Radially outward
Answer: D. Radially outward. A positive test charge is repelled from a positive source charge.
If separation between two point charges doubles, their Coulomb force becomes what?
A One half
B Twice as large
C One quarter
D Four times larger
Answer: C. One quarter. Coulomb force varies inversely as separation squared.
Which charge does Gauss’s law use for flux through a closed surface?
A Nearby external charge
B Enclosed charge
C Surface area alone
D Conductor mass
Answer: B. Enclosed charge. Net electric flux depends on the total charge inside the closed surface.
Inside the material of an electrostatic conductor in equilibrium, E is what?
A Always infinite
B Equal to current
C Zero
D Tangential only
Answer: C. Zero. Mobile charges rearrange until the bulk electric field vanishes.
How does an electrostatic field meet an equipotential surface?
A Tangentially
B At every angle equally
C It never meets
D Perpendicularly
Answer: D. Perpendicularly. A tangential field would change the potential along the surface.
Moving a charge along one equipotential surface requires what net electrostatic work?
A Maximum work
B Zero
C Infinite work
D Always negative work
Answer: B. Zero. Potential difference is zero along an equipotential surface.
Capacitance of a two-terminal capacitor is defined by which ratio?
A Q/V
B V/Q
C Q×V
D I/V
Answer: A. Q/V. Capacitance is stored charge divided by terminal voltage.
For a linear isotropic dielectric, which relation links D and E?
A D = εE
B D = E/ε
C D = μE
D D = ε/E
Answer: A. D = εE. Electric flux density equals permittivity times electric-field intensity.
Relative permittivity compares a material’s permittivity to what?
A Vacuum permittivity
B Magnetic permeability
C Free-space impedance
D Vacuum flux density
Answer: A. Vacuum permittivity. εr is the dimensionless ratio ε/ε0.
Which field stores the energy of an ideal capacitor?
A Magnetic field only
B Gravitational field
C Electric field
D Acoustic field
Answer: C. Electric field. Capacitor energy resides in its electric field.
What is the SI unit of magnetic flux density B?
A Weber
B Henry
C Siemens
D Tesla
Answer: D. Tesla. Magnetic flux density is measured in teslas.
Which unit belongs to magnetic-field intensity H?
A Wb/m
B V/m
C F/m
D A/m
Answer: D. A/m. H is measured in amperes per metre.
In a linear isotropic magnetic medium, how are B and H related?
A B = H/μ
B B = εH
C B = μH
D B = μ/H
Answer: C. B = μH. Permeability μ links flux density and field intensity.
Around a long straight current-carrying wire, the magnetic lines form what?
A Radial rays
B Concentric circles
C Parallel planes
D Open spirals
Answer: B. Concentric circles. The magnetic field circles the wire according to the right-hand rule.
Magnetostatic Ampère’s circuital law relates ∮H·dl to what?
A Enclosed current
B Enclosed charge only
C Electric potential
D Magnetic mass
Answer: A. Enclosed current. The line integral of H around a closed path equals enclosed free current.
What SI unit measures magnetic flux?
A Tesla per metre
B Weber
C Ampere
D Ohm
Answer: B. Weber. One weber is one tesla square metre of magnetic flux.
A changing magnetic flux through a coil produces which effect?
A Static charge only
B Induced emf
C Zero electric field
D Fixed resistance
Answer: B. Induced emf. Faraday’s law relates induced emf to the rate of flux-linkage change.
Lenz’s law sets the direction of induced current to oppose what?
A Original conductor length
B Earth gravity
C Flux change
D Ohmic heating
Answer: C. Flux change. The induced effect opposes the change that produced it.
A charge q moving with velocity v in magnetic field B experiences which magnetic force?
A q(v×B)
B q(v·B)
C qB/v
D qE only
Answer: A. q(v×B). The magnetic part of Lorentz force is the cross product q(v×B).
Why does the magnetic force on a moving point charge do no work?
A Force is always zero
B Force is perpendicular to velocity
C Charge has no mass
D B is always zero
Answer: B. Force is perpendicular to velocity. The v×B force has no component along the particle’s motion.
Maxwell’s displacement-current term is associated with what?
A Static resistance alone
B Constant magnetic flux
C Time-varying electric field
D Mechanical friction
Answer: C. Time-varying electric field. The time derivative of electric displacement appears in Ampère–Maxwell law.
In a uniform plane wave in an isotropic medium, how do E, H and propagation direction align?
A All parallel
B E parallel to H
C H opposite E
D Mutually perpendicular
Answer: D. Mutually perpendicular. In a transverse plane wave, E and H are perpendicular to each other and to propagation.
What direction does the Poynting vector E×H indicate?
A Electric charge motion only
B Magnetic pole orientation
C Potential gradient
D Energy flow
Answer: D. Energy flow. E×H points in the direction of electromagnetic energy transport.