Refraction occurs when light crosses the boundary between one material and another material. what is the primary cause for this refracting of light upon crossing a boundary?

According to social exchange theory, altruistic behaviors benefit the individual who performs them. t/f

Balloon a has charge q, and identical mass balloon b has charge 10q. you hang them from threads near each other. choose all of the statements with which you agree. check all that apply. a. a and b exert the same magnitude forces on each other. b. the force that a exerts on b is 10 times the force that b exerts on a. c. the angle between the thread supporting a and the vertical is < the angle between the thread supporting b and the vertical. d. the force that a exerts on b is 1/10 the force that b exerts on a.

Give an example in which the electrical energy changes to light energy