# A level physics question

Fig. 3.1 shows a simple representation of a hydrogen iodide molecule. It consists of two ions
1
1H+ and 127
53 I −, held together by electric forces.
H+ I

Fig. 3.1
(a) (i) Draw on Fig. 3.1 a minimum of five lines to show the electric field pattern between the
ions. [2]
(ii) The charge on each ion has a magnitude e of 1.6 × 10−19C. The ions are to be treated
as point charges 5.0 × 10−10m apart. Calculate the magnitude of the resultant electric
field strength E at the mid-point between the ions.

For part ii, i got E of H to be +2.3x10^10 and E of I to be -2.3x10^10 why is the resultant magnitude 4.6x10^10 and not 0NC^-1?
Remember that electric fields are VECTOR quantities (i.e. they have a direction). Also, field lines can only start or end on charges. Both e-fields from the H+ and I- ions are pointing from the ions to the mid-point. So, to correctly combine the two fields, you need to subtract them, and hence the magnitude of the resultant is twice the individual magnitude.
Original post by lordaxil
Remember that electric fields are VECTOR quantities (i.e. they have a direction). Also, field lines can only start or end on charges. Both e-fields from the H+ and I- ions are pointing from the ions to the mid-point. So, to correctly combine the two fields, you need to subtract them, and hence the magnitude of the resultant is twice the individual magnitude.

Nvm, i get it now its bc both act in the same direction as it is a positive charge, repelled from the -ve and attracted to the +ve, but thanks