Suppose you pull off husk leaves on an ear you shucked out of the field. You want to do the simple shake test on the ear to see how many silks fall off. Bob Nielsen, Purdue University Extension corn specialist, has explained to you that if the pollen grain went down the tube, which is basically the silk, and did its job, the ovule will be fertilized and a kernel will begin to form. Shortly afterwards the silk will begin to dry up at the point of attachment. Then it will fall off the ear.
Conversely, if pollination didn't occur, then the silks will remain attached. Each attached silk means that an ovule didn't get fertilized, and a kernel won't form there.
What some people are reporting who do have corn with ears in hard-hit areas by the heat and drought is that ears are only medium size to begin with. That's primarily in length. Then when you do the shake test, as much as two inches of the cob nearest the tip retains silks. The silks fall off up to that point. The conclusion is that the ear pollinated up to the tip, and then either due to heat, stress or both, the kernels at the tip of the ear didn't pollinate.
Of course, there are various explanations. It could be that pollination is still in the middle of the process, and you happened to scout the field and grab the ear before pollination was complete. It begins at the base, or butt, of the ear and progresses upwards to the tip. It could be that those ovules retaining silks out near the tip simply needed more time. As long as pollen is still being shed in the field, there's a chance for those ovules to be fertilized and become kernels.It's also possible that fertilization didn't occur because there wasn't enough pollen left then the ear was ready to finish pollination, or else that portion of the ear attempted to pollinate on an extremely hot, dry day and wasn't successful. Check several ears to get a better handle on what kind of pollination success happened in the field.