1. Electric Charges and Fields
easy

Two small conducting spheres of equal radius have charges $ + 10\,\mu C$ and $ - 20\,\mu C$ respectively and placed at a distance $R$ from each other experience force ${F_1}$. If they are brought in contact and separated to the same distance, they experience force ${F_2}$. The ratio of ${F_1}$ to ${F_2}$ is

A

$1:8$

B

$-8:1$

C

$1:2$

D

$-2:1$

Solution

(b) $F \propto {Q_1} {Q_2}$

$\frac{F_1}{F_2}$$ = \frac {{Q_1}{Q_2}} {{Q'_1}{Q'_2}}$$ = \frac{{10 \times  – 20}}{{ – 5 \times  – 5}} $$= \frac{{ – 8}}{1}$

Standard 12
Physics

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