19) Two electrons are 20.0mm apart at closest approach. What is the magnitude of

Question

19) Two electrons are 20.0mm apart at closest approach. What is the magnitude of the maximum electric force that they exert on each other? (e = 1.60 × 10-19 C, k = 1/40 = 9.0*109 N · m2/C2)

A) 5.8 × 10-25 N

B) 2.3 × 1010 N

C) 2.3 N

D) 5.8 × 10-27 N

20) A small object with a 5.0-µC charge is accelerating horizontally on a friction-free surface at 0.0050 m/s2 due only to an electric field. If the object has a mass of 2.0 g, what is the magnitude of the electric field?

A) 2.0 N/C

B) 4.0 N/C

C) 0.0020 N/C

D) 0.0040 N/C

E) 1.0 N/C

21) A parallel-plate capacitor is constructed of two square plates, size L x L separated by distance d. The plates are given charge ± Q. What is the ratio of the final electric field strength to the initial electric field strength if L is reduced to half?

A. 0.25

B. 4

C. 0.5

D. 1

Explanation / Answer

19) F =kq^2 /r^2. =9×10^9×(1.6×10^-23)^2 /0.02^2

= 5.8 × 10^-25 N

option A is correct

20)E= ma/q =0.002×0.005/(5×10^-6) = 2 N/C

option A is correct

21) when L becomes half, area becomes one fourth, capacitance becomes one fourth and voltage becomes 4 times and electric field 4 times..

B option is correct

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