What are the differences between p waves and s waves?

What are the densities of the crust, mantle, outer core and inner core?

What causes convection currents in the mantle?

What is the difference between an AC and a DC?

What is electromagnetic induction?

What does it mean when the reading of the magnet shows a) 0 b) positive c) negative?

How is electricity generated from fossil fuels?

How does a dynamo on bikes turn the light?

How to increase the current?