A charge $q_1$ exerts a force of $45N$ on a charge of $q_2=10^{-5}C$ located at a point $0.2m$ from $q_1$. The magnitude of $q_1$ is

Two concentric, thin metallic spherical shells of radii $R_1$and$R_2(R_1>R_2)$ bear charges $Q_1$ and$Q_2$  respectively. Then the potential at radius ‘r’ between $R_1$ and $R_2$will be $\frac{1}{4\pi {ϵ}_0}$ times

Four chargers $q_1=-0.02\mu C$, $q_2=+0.04\mu C$, $q_3=+0.02\mu C$, and $q_4=-0.04\mu C$ are at the four corners of a square of side $9cm$ . Then the potential at the centre of the square is :

Two point charges $q_1=2\mu C$ and $q_2=1\mu C$ are placed at distances $b=1cm$ and $a=2cm$ from the origin on the y and x axes as shown in figure. The electric field vector at point $(a,b)$ will subtend an angle $\theta$ with the x - axis given by :

The potential at the origin is zero due to electric field $\bar{E}=20\hat{i}+30\hat{j}N{C}^{-1}$ . The potential at point $P(2m,2m)$ is: