What causes friction between two seemingly smooth surfaces?

a. the surfaces really aren't smooth. it's just an illusion.

b. surfaces that are too smooth tend to stick together.

c. tiny collisions on the surfaces, called microwelds, cause friction.

d. there is an invisible force sticking the surfaces together.

dopamine..

"it was found that some people who were taking the drug l-dopa to raise their levels of dopamine were developing schizophrenic-like symptoms supporting research a strength of the dopamine hypothesis is that there are many studies which have shown support for the neurochemical explanation."

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.

conduct current i mean it makes sense