1. if the coulomb force between two charges F , is given , the separation between the charges of magnitude Q1 and Q2  r is given, this formula  where k is a constant  where d=π. and E=permittivity of free space.
2. When electric field intensity E, on the charge of magnitude q is given and the coulomb force is given, from  , we can make q the subject of the formular and calculate the charge.
3. if electric potential V on the charge Q is given, which is the workdone in bring the a unit charge from infinity to any point, then from  where  where d=π , we can make any term the subject of the formula and calculate the charge it.
4. in a question where  the potential difference between two charges  q1 and q2  at a distance x and y is given  we can use  this relation V=  can be used to calculate any term in the above formular.
5.  if electric field intensity of any charge  q under effect of coulomb force is given by  .
6.  electric potential on any charge q is given by  where  where d=π ,.
7.  to calculate force between two charges q1 and q2 , we use .
8. to find quantity of charge  Q when a current I is passed through a conductor in a time t, from   and Q=It.
9. If n number of charge q,  pass through a conductor of length L, cross-sectional area A, the quantity of charge Q is given by Q=qnAL. and q=Q/nAL
10. from number 9, if the charge has a drift velocity of vd Then the quantity of charge Q, will be given by .
11. note  if quantities are given in sub-units ensure you convert them to actual units before substituting them,  e.g if current are given in microamps ensure you convert them to amperes ,you can reconvert back them after solving the problem if you wish to do so.
12. if the question involve the phenomenon of  hall effect  ,it is given as , where B is the magnetic field intensity.
13. to calculate hall voltage , we use this equation ,   where I is the current,  B is the magnetic field, d is the width of the conductor and A is the cross-sectional area. we can find value of any of the parameter given above by making it the subject of the relations.
14. if the hall coefficient is we can use this equation given and then
15. for a charge particle moving in magnetic field in a circular path of radius r ,  is the force acting on it, it has an angular frequency ω of   and period T, of  and frequency of ,
16. for mass spectrometer, the mass to charge ratio is given by  where E=ℇ and r is the radius, B and B0 are the initial and final magnitude  magnetic fields respectively ,
17. for a particle of charge q in a cyclotron,  the kinetic energy is given by and the frequency is  where d=π.
18. total charge in close sphere is given by , total flux =q/ℇ , where  ℇ is permittivity of free space.
19. the flux intensity in a sphere  is given by  where d=π and E=ℇ
20. in a charge plane conductor of density σ, charge intensity is given by E= σA/ℇ
21. For capacitor, C=Q/A and for parallel plate C=ℇA/d.