Pure silicon contains approximately 1.0 x 1016 free electrons per cubic meter. ( a. referring to table 25.1, calculate the mean free time., for silicon at room temperature. ( b. your answer in part ( a. is much greater than the mean free time for copper given in example 25.12. why, then, does pure silicon have such a high resistivity compared to copper?

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

54 degrees incident angle = reflected angle

angle is from normal turned to line of ray