a level chem- van der waals forces doubtWatch
The dipole is caused by the changing position of the electron cloud, so the more electrons there are. the larger the instantaneous dipole will be.
does it mean larger in terms of size? or larger as in stronger?
We always talk in terms of strength - more electrons means that as they move around, there will be greater differences in the uneven distribution of charge across the molecule which leads to a greater instantaneous dipole. As a result, the strength of attraction between such molecules will be greater.