What's the difference between an Intel Core i3, i5 and i7?

We've seen many years now of Intel Core i3, Core i5, and Core i7 CPUs releases but most consumers are still asking the same kinds of questions. What's the difference and is it worth paying more for a CPU with more cores?

What is the difference between Intel Core i3, i5 and i7? - PC World Australia

What is the physical difference between the Intel i3, i5, and i7 and how significant of a difference is created performance wise? - Quora

i5 vs i7 - Difference and Comparison

What is a Core i3, Core i5, or Core i7 as Fast As Possible

What's the difference between an Intel Core i3, i5 and i7?

What is the difference between Intel Core i3, i5 and i7? - PC World Australia

Difference Between Intel Core i3,i5 & i7 Processors

Core i3, Core i5 & Core i7 ! Technology Explained!

Intel Processors Explained: What Is Core I3, I5, I7 And Pentium? - Which?

What is the physical difference between the Intel i3, i5, and i7 and how significant of a difference is created performance wise? - Quora

Intel Core I3 Vs I5 Vs I7 Comparison: What CPU Should You Choose Right Now?