Which statements are true for two oppositely charged, isolated parallel plates:

Question

Which statements are true for two oppositely charged, isolated parallel plates: C=capacitance, U=stored energy (Q and -Q = charge on The plates). True When The distance is halved, Q stays The same. False Inserting a dielectric increases Q. True Inserting a dielectric increases C. False When The distance is doubled, U increases. False Increasing The distance increases The Electric field. False Inserting a dielectric decreases U. Isolated means that The charge stays constant submit Answer incorrect. Tries 1/20 Previous Tries

Explanation / Answer

For oppositely charged isolated parallel plates,

C = A/d, U = Q2/2C = Q2d/2A, E = V/d = Q/Cd = Q/A

where = permittivity of the medium between plates, A = area of the plates, d = distance between plates, E = Electric field between the plates, V = Voltage across plates

(a) When the diatance is doubled, C increases.

FALSE ( C 1/d)

(b) When the distance is halved, Q remains the same.

TRUE (Isolated plates cannot lose or gain charge)

(c) Inserting a dielectric increases Q

FALSE (Q cannot change)

(d) Inserting a dielectric increases C

TRUE ( C and = ko > o  in case of dielectrics where k > 1)

(e) When the distance is doubled, U increases

TRUE (U d)

(f) Increasing the distance increases the electric field

FALSE (Electric field doesn't depend on distance between plates since E = Q/A)

(g) Inserting a dielectric decreases U

TRUE (Q 1/ and > o for dielectric)

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