Answer:

Explanation:
It is given that,
Initially, the electron is in n = 7 energy level. When it relaxes to a lower energy level, emitting light of 397 nm. We need to find the value of n for the level to which the electron relaxed. It can be calculate using the formula as :


R = Rydberg constant, 

Solving above equation we get the value of final n is,

or

So, it will relax in the n = 2. Hence, this is the required solution.
You could use the formula
W=Fd
F(force)=20N
D(distance/displacement) =15m
W=(20N)(15m)
W= 300 J
Answer:
136000 J or 136 kJ
Explanation:
Formula
Heat = m * c * deltaH
Givens
m= 0.5 kg
c = 3400 J / (kg * oC)
Deltat = (100oC - 20oC)
deltat = 80oC
Solution
Heat = 0.5 kg * 3400 J/(kg* oC) * 80oC
Heat = 136000 Joules
Heat = 136 kg
Technically there is only 1 place of accuracy.
It's the 3rd one bc they are produced by beta decay