OUT OF BOOK QUESTION
An ideal air‐filled parallel‐plate capacitor has round plates and carries a fixed amount of equal but opposite charge on its plates. All the geometric parameters of the capacitor (plate diameter and plate separation) are now DOUBLED. If the original capacitance was C0, what is the new capacitance?
A) 4C0
B) 2C0
C) C0
D) C0/2
E) C0/4
Answer: B
OUT OF BOOK QUESTION
The charge on the square plates of a parallel‐plate capacitor is Q. The potential across the plates is maintained with constant voltage by a battery as they are pulled apart to twice their original separation, which is small compared to the dimensions of the plates. The amount of charge on the plates is now equal to
A) 4Q.
B) 2Q.
C) Q.
D) Q/2.
E) Q/4.
Answer: D
OUT OF BOOK QUESTION
The electric field between square the plates of a parallel‐plate capacitor has magnitude E. The potential across the plates is maintained with constant voltage by a battery as they are pulled apart to twice their original separation, which is small compared to the dimensions of the plates. The magnitude of the electric field between the plates is now equal to
A) 4E.
B) 2E.
C) E.
D) E/2.
E) E/4.
Answer: D
OUT OF BOOK QUESTION
A parallel‐plate capacitor has plates of area 0.40 m2 and plate separation of 0.20 mm. The capacitor is connected across a 9.0‐V potential source. (ε0 = 8.85 × 10‐12 C2/N ∙ m2)
(a) What is the magnitude of the electric field between the plates?
(b) What is the capacitance of the capacitor?
(c) What is the magnitude of the charge on each plate of the capacitor?
(c) What is the magnitude of the surface charge density on each plate of the capacitor?
Answer: (a) 4.5 × 104 N/C (b) 18 nF
(c) 160 nC (d) 4.0x10‐7 C/m2
OUT OF BOOK QUESTION
Two thin‐walled concentric conducting spheres of radii 5.0 cm and 10 cm have a potential difference of 100 V between them. (k = 1/4πε0 = 8.99 × 109 N ∙ m2/C2)
(a) What is the capacitance of this combination?
(b) What is the charge carried by each sphere?
(c) What is the magnitude of surface charge density of inner and outer spheres?
Answer: (a) 11 pF (b) 1.1 nC
(c) inner: 35 nC/m2 outer: 8.8 nC/m2
OUT OF BOOK QUESTION
A metal cylinder of radius 2.0 mm is concentric with another metal cylinder of radius 5.0 mm. If the space between the cylinders is filled with air and the length of the cylinders is 50 cm, what is the capacitance of this arrangement?
(k = 1/4πε0 = 8.99 × 109 N ∙ m2/C2)
A) 33 pF
B) 60 pF
C) 22 pF
D) 30 pF
E) 11 pF
Answer: D
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