Displacement current — practice questions

Question 1 · difficulty L1 · recall

Maxwell introduced displacement current to account for

• A. a changing electric field producing magnetic effects
• B. steady charges producing no fields
• C. only conduction electrons in metals
• D. magnetic monopoles

Question 2 · difficulty L1 · understanding

Between the plates of a charging capacitor, conduction current through the dielectric gap is ideally

• A. equal to infinite current
• B. zero
• C. larger than wire current
• D. always negative

Question 3 · difficulty L2 · understanding

The displacement current is proportional to the rate of change of

• A. magnetic charge
• B. mechanical momentum
• C. electric flux
• D. resistance

Question 4 · difficulty L2 · application

For a charging capacitor in a simple series circuit, the displacement current between the plates is

• A. always zero
• B. twice the conduction current
• C. unrelated to circuit current
• D. equal in magnitude to the conduction current in the wires

Question 5 · difficulty L3 · application

If the electric field between capacitor plates changes twice as fast while geometry is fixed, displacement current becomes

• A. twice as large
• B. half as large
• C. four times as large
• D. unchanged

Question 6 · difficulty L3 · application

A fully charged ideal capacitor is connected to steady DC and has constant electric field. Its displacement current is

• A. maximum
• B. zero
• C. equal to V/R indefinitely
• D. independent of field change

Question 7 · difficulty L4 · analysis

Why was displacement current essential to Maxwell's extension of Ampere's law?

• A. It removes electric fields from capacitors
• B. It proves magnetic monopoles exist
• C. It makes the magnetic-field law consistent through surfaces crossing a charging capacitor gap
• D. It replaces conduction current in all wires

Question 8 · difficulty L4 · analysis

A parallel-plate capacitor of area A has uniform field changing at rate dE/dt. The vacuum displacement current is

• A. ε0 E/A
• B. A/(ε0 dE/dt)
• C. ε0 A E
• D. ε0 A dE/dt

Question 9 · difficulty L5 · analysis

If capacitor plate area is doubled while dE/dt stays the same, displacement current

• A. doubles
• B. halves
• C. remains unchanged
• D. becomes one-fourth

Question 10 · difficulty L5 · analysis

A current meter inserted in the wire feeding a charging capacitor reads I. An Amperian analysis through the gap must attribute what current to the gap region?

• A. Zero total current of every kind
• B. Displacement current I
• C. Conduction current 2I
• D. A current depending only on plate spacing