If i run google ads on my site and someone clicks an ad i earn money right. Are some ad clicks more expensive then others?

Yes it depends on the nich like morgage and layers get more then shoe strings (obviously no one would search that or buy those online so theres less of a market for advertizing)

Let me simplify my question. I have a website with google ads. The ads alternate randomly. Let say we have three ads i.e.

1. iq test
2. web hosting offer
3. buy cars in japan

could it be that if someone clicks buy cars in japan i would earn more revenue then if someone had clicked the iq test?

yes its depend on your niche..if you run ads for insurance then you will be paid more because of competitive niche