Which of the following factors determines the strength of the frictional force between two surfaces

Explanation:

The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved. What factors affect the gravitational force between two objects? Two factors affect the gravitational attraction between objects: mass and distance.

How hard the surfaces push together, and the types of surfaces involved

Explanation:

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.

so easy. just google the electromagnetic waves and it’ll pop up.