empty tags don't show the space. I can see tags in my code firebug

I tried to enter empty p tags that is <p></p>
To get some space below an image.
But it does not show the space.
I can see the tag in firebug.
In firebug I tried adding a 100 empty p tags as show above.
It still did not show the space.
But as soon as I enter any text in between those tags (In Firebug) it shows up immediately.
I am just lost I tried to search but it keeps throwing me results to queries on TinyMC editor adding empty tags.
So I am posting it here.
Please Help
Thank you