It has to be used because you can not visually see them
Answer:
A. a rigorously tested explanation
Explanation:
- B. and D. are out - theories are not opinionated, they are factual
- C. is out - not all theories are mathematical
- A. is the best choice
Answer:
B. use light of a shorter wavelength.
Explanation:
We know that

h= plank's constant
c= speed of light
λ= wavelength of the incident light
so, in order to have sufficient energy for for the emission of electron, the incident's radiation must have λ small enough.
B. use light of a shorter wavelength.
41.5 is the answer that i got. hope this helps!
Explanation:
Joule (J) is the MKS unit of energy, equal to the force of one Newton acting through one meter.