For any fixed distance,the electromagnetic force between two protons is $10^n$ times the gravitational force between them. Then $n=$

Equal charges $q$ are placed at the four corners $A, B, C, D$ of a square of side length $a$. The magnitude of the net electrostatic force on the charge at $B$ is:

Two identical conducting spheres,having charges of opposite sign,attract each other with a force of $0.108 \ N$ when separated by $0.5 \ m$. The spheres are connected by a conducting wire,which is then removed,and thereafter,they repel each other with a force of $0.036 \ N$. The initial charges on the spheres are

Two identical spheres,each of mass $1 \, g$,carry an identical charge of $10^{-9} \, C$. They are suspended by strings of equal length. If the distance between the centers of the spheres is $0.3 \, cm$,what is the angle made by the string with the vertical?

Two particles with charges $+3.72 \mu C$ and $+1.86 \mu C$ are at some distance apart. If $20 \%$ of the charge is transferred from the first particle to the second particle,then the electrostatic force between them is

Two point charges $+8 \mu C$ and $+12 \mu C$ repel each other with a force of $48 \ N$. When an additional charge of $-10 \mu C$ is given to each of these charges (the distance between the charges is unaltered),then the new force is: