The 1000 small droplets of water each of radius $$r$$ and charge $$Q,$$ make a big drop of spherical shape. The potential of big drop is how many times the potential of one small droplet ?
A.
1
B.
10
C.
100
D.
1000
Answer :
100
Solution :
Volume of big drop $$ = 1000 \times {\text{volume}}\,{\text{of}}\,{\text{each}}\,{\text{small}}\,{\text{drop}}$$
$$\eqalign{
& \frac{4}{3}\pi {R^3} = 1000 \times \frac{4}{3}\pi {R^3} \Rightarrow R = 10r \cr
& \because V = \frac{{kq}}{r}\,{\text{and}}\,V' = \frac{{kq}}{R} \times 1000 \cr} $$
Total charge on one small droplet is $$q$$ and on the big drop is $$1000\,q.$$
$$\eqalign{
& \Rightarrow \frac{{V'}}{V} = \frac{{1000r}}{R} = \frac{{1000}}{{10}} = 100 \cr
& \therefore V' = 100\,V \cr} $$
Releted MCQ Question on Electrostatics and Magnetism >> Electric Potential
Releted Question 1
If potential (in volts) in a region is expressed as $$V\left( {x,y,z} \right) = 6xy - y + 2yz,$$ electric field (in $$N/C$$ ) at point $$\left( {1,1,0} \right)$$ is
A.
$$ - \left( {3\hat i + 5\hat j + 3\hat k} \right)$$
B.
$$ - \left( {6\hat i + 5\hat j + 2\hat k} \right)$$
C.
$$ - \left( {2\hat i + 3\hat j + \hat k} \right)$$
D.
$$ - \left( {6\hat i + 9\hat j + \hat k} \right)$$
A conducting sphere of radius $$R$$ is given a charge $$Q.$$ The electric potential and the electric field at the centre of the sphere respectively are
A.
zero and $$\frac{Q}{{4\pi {\varepsilon _0}{R^2}}}$$
B.
$$\frac{Q}{{4\pi {\varepsilon _0}R}}$$ and zero
C.
$$\frac{Q}{{4\pi {\varepsilon _0}R}}{\text{and}}\frac{Q}{{4\pi {\varepsilon _0}{R^2}}}$$
In a region, the potential is represented by $$V\left( {x,y,z} \right) = 6x - 8xy - 8y + 6yz,$$ where $$V$$ is in volts and $$x,y,z$$ are in metres. The electric force experienced by a charge of $$2C$$ situated at point $$\left( {1,1,1} \right)$$ is
Four point charges $$ - Q, - q,2q$$ and $$2Q$$ are placed, one at each corner of the square. The relation between $$Q$$ and $$q$$ for which the potential at the centre of the square is zero, is