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the surface of a metal plate is illuminated with light of a certain frequency. which of the following conditions determine whether or not photoelectrons are ejected from the metal?
1. the number of photons per second emitted by the light source
2. the length of time that the light is turned on
3. the thermal conductivity of the metal
4. the surface area of the metal illuminated by the light
5. the type of metal from which the plate is made
a) 3 and 5
b) 4
c) 5
d) 2 and 3
e) 1 and 2

The correct answer is option '5': The type of metal from which the plate is made.

Explanation:

According to the principle of photoelectric effect we know that electron's are only emitted from a surface of metal if the frequency of the light is larger than a threshold frequency that depends on the metal and is known as threshold  function of the metal. The ejection of the electrons is independent of intensity of the incident light meaning any light of frequency lower than work function will not eject electrons from the metal no matter whatever the intensity of the light, or the surface area or thermal conductivity, time of illumination.

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.