Gaokao Physics: Electromagnetism Flashcards

A charged particle with charge q and mass m is accelerated from rest through a potential difference V, then enters a magnetic field B perpendicular to the field. The radius of its circular motion is:

Answer: √(2mV/q)/B

From ½mv² = qV: v = √(2qV/m); then r = mv/(qB) = m√(2qV/m)/(qB) = √(2mV/q)/B.

Kirchhoff's current law (KCL) is based on the principle of:

Answer: Conservation of charge

KCL states that the algebraic sum of currents at any junction is zero, reflecting charge conservation.

The SI unit of inductance is the Henry (H). 1 H is equivalent to:

Answer: All of the above are equivalent

1 H = 1 V·s/A (from EMF = L dI/dt) = 1 T·m²/A (from flux linkage) = 1 Ω·s; all three expressions are dimensionally equivalent.

An electric dipole consists of charges +q and −q separated by distance d. The electric field at the midpoint between the charges is directed:

Answer: From +q toward −q

Both charges produce fields at the midpoint; the +q field points away from +q (toward −q) and the −q field also points toward −q; they add in the same direction.

A generator converts mechanical energy to electrical energy. The process is governed by:

Answer: Faraday's law of electromagnetic induction

Generators work by rotating coils in magnetic fields, inducing EMF according to Faraday's law.

The dielectric constant of a material inserted between capacitor plates, compared to vacuum, causes the capacitance to:

Answer: Increase by a factor equal to the dielectric constant

C = κε₀A/d; inserting a dielectric increases capacitance by factor κ (the dielectric constant).

The phase relationship between current and voltage in a purely inductive AC circuit is:

Answer: Current lags voltage by 90°

For a pure inductor, V = L(dI/dt); if I = I₀sinωt then V = LωI₀cosωt, so voltage leads current by 90° (or current lags voltage by 90°).