Each plate of a parallel-plate air-filled capacitor has an area 0.0020 m^2, and

Question

Each plate of a parallel-plate air-filled capacitor has an area 0.0020 m^2, and the separation of the plates is 0.020 mm An electric field of 3.9 times 10^-6 v/m is present between the plates. What is the surface charge density on the plate ? (epsilon_0 = 8.55 times 10^-12 C^2/N-m^2) 52 mu C/m^2 73 mu C/m^2 17 mu C/m^2 87 mu C/m^2 35 mu C/m^2 The figure shows two connected wires that are made of the same material. The current entering the wire on the left is 2.0 A and in that wire the electron drift speed is. What is the electron drift speed in the wire on the right side? v_d/2 v_d v_d/4 4v_d 2v_d An electric device delivers a current of 5.0 A to a device. How many electrons flow through this device in 10 s? 0.20 31 times 10^20 2.0 3.0 times 10^20 20 If a current of 2.4 A is flowing in a cylindrical wire of diameter 2.0 mm, what is the average current density in this wire? 5.2 times 10^-6 A/m^2 21 times 10^-6 A/m^2 7.6 times 10^5 A/m^2 3.6 times 10^5 A/m^2 1.9 times 10^5 A/m^2 Thirteen resistors are connected across points A and B as shown in the figure. If all the resistors are accurate to 2 significant figures, what is the equivalent resistance between points A and B? 4.0 ohm 10 ohm 6.0 ohm 12 ohm 8.0 ohm

Explanation / Answer

6)  Most of the info' isn't needed.

Field strength = E
sigma (Greek letter) = surface charge density in C/m^2
epsilon_0 = permittivity of free space.

E = sigma / epsilon_0

3.9E6 = sigma / 8.85E-12

sigma = 3.9E6 x 8.85E-12
= 3.5E-5 C/m^s
= 3.5E-5 x 1E6 µC/m^2
= 35µC/m^2 (answer e)

8) Number of electrons ( N ) = ( I x t ) / e
I = 5A
t = 10s
e = 1.6 10^-19

N = 5 * 10 / 1.6 10^-19 = 3.1* 10^20

9) Answer: C
Comment: j = I/A = 2.4 / (pi d^2/4) = 7.6 × 10^5 A/m2

10) Answer: B
Comment: Working from the right side and combining the resistors according to
parallel and series connection rules, we obtain 8 ohm

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