Both answers are E but how so? A parallel plate capacitor is manufactured with a

Question

Both answers are E but how so?

A parallel plate capacitor is manufactured with a plate area of 3.0 m2 and a plate spacing of 0.7 mm. It is desired to obtain a maximum charge on the capacitor of 87 C when it is connected to a 12 V battery. What dielectric constant is needed in the 12. capacitor to obtain this maximum charge? A 3.0 m2 d=0.000 Ino A 355.6 B 233.7 C 96.8 D 482.3 E 191.1 3853 An electric field is created in the atmosphere during a thunder storm that is 9,700 N/C directed down toward the ground. A charged object, q, with a mass of 0.04 grams is drifting through the air and is then accelerated upward by this electric field at 520 m/s2. What are the sign and magnitude of the electric charge, q? The forces by gravity and air resistance are much smaller than the electric force on the charge and can be neglected. 13. -5.6le-006 C -4.21e-006 C C) 2.14e-006 C 100 1 D 4.21e-006 C E -2.14e-006 C

Explanation / Answer

12. Q = C V

87uC = C ( 12 V)

C = 87/12 = 7.25 uF  

and C = k e0 A / d

7.25 x 10^-6 = (8.854 x 10^-12)(k) (3) / (0.7 x 10^-3)

k = 191.1

13. electric force is upwards and E is donwnwards.

F = q E

F and E have opposite direction so q is negative.

and a = F / m = q E / m

520 = (q) (9700) / (0.04 x 10^-3)

q = 2.14 x 10^-6 C

so ANs: q = - 2.14 x 10^-6 C

  

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