What is the period of a wave if 20 crests pass an observer in 4 seconds? 80 s
0.2 s
5 s
4 s

Modern physics a photon emitted from an excited hydrogen atom has an energy of 3.02 electron volts. which electron energy-level transition would produce this photon? a. n=1 to n=6 b. n=2 to n=6 c. n=6 to n=1 d. n=6 to n=2 i chose b but the correct answer is d can someone tell me why? and what's the difference?

Which of the following are guidelines to follow for obtaining accurate observations

Wind and moving water provide energy. question 1 options: chemical mechanical thermal none of the above