2. *Two point charges, one tq and the other -q, form a dipole separated by a dis

Question

2. *Two point charges, one tq and the other -q, form a dipole separated by a distance d. A third charge Qis placed midway between these two charges. If the distance between the +q and the -q is then doubled with the Q staying midway between the other two, what happens to the force on Q? a. It halves. b. It reduces by a factor of 8 c. It stays the same. d. It quarters. 3. *What is the equivalent capacitance of the combination shown? a. 29F b. 10F c. 40 pF d, 25 F 4. *If an electron is accelerated from rest through a potential difference of 1800 v find its approximate velocity at the end of this process. a. 2.8x10 m/s b. 25.2x10 m/s c. 2.5x107 m/s d. 6.3x10' m/s

Explanation / Answer

2. Fe = 2 [ k Q q / (d/2)^2]

Fe = 8 k Q q / d^2

d-> 2d

so Fe -> Fe / 4

Ans(d)

3. 12 and 24uF are in series.

1/C = 1/12+ 1/24

C = 8 uF  

Now C and 12uF are in parallel,

c' = 12 + 8 = 20 uF  

Now two 20uF are in series,

Ceq = 20/2 = 10 uF  

Ans(b)

4. KE = q delta(V)

(9.109 x 10^-31) v^2 / 2 = (1.6 x 10^-19)(1800)

v = 2.5 x 10^7 m/s

Ans(c)

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