Q: Why did the scientist install a knocker on his front door?
A: Because he wanted to win the no-bell prize!
Explanation: A knocker is that metal piece on the outside of a door that you use to make noise so that people know that you are there. An alternative to using a door knocker is to use a doorbell. A doorbell is a button, typically found next to the door, that you push to make noise inside the house so that people know that you are there.
If you do not have a doorbell, you have no bell. “No bell” sounds like Nobel. Nobel is the name of a prize in many different categories including physics, chemistry, peace, and literature.
This joke is funny because no-bell sounds like Nobel, and the scientist wanted to win a no-bell/Nobel prize. (That strategy probably won’t help him win!)
Here is some information about the Nobel Prizes: