What is (a) the wavelength of a 5.40-ev photon and (b) the de broglie wavelength of a 5.40-ev electron?

(a) for a photon, the relationship between frequency f and energy E is
(1)
where h is the Planck cosntant.

First, we need to convert the energy from eV to Joule:


Then, using (1) we can find the frequency of the photon:


and finally we can find its wavelength:


(b) now we have to find the De Broglie wavelength of an electron with same energy of the previous photon. Again, we must convert the energy in Joules first:


Then we can use the relationship between momentum p and energy E of a particle, to find p: (electron mass:  )



And finally we can use De Broglie relationship to find the wavelength of the electron:

Answer: it will take   4.36 seconds to reach her average velocity 10.69 miles/hour.explanation:   we have equation of motion ,where s is the displacement, a is the acceleration, u is the initial velocity and t is the time taken.average velocity = displacement/ time taken.average velocity = 10.69 miles/hr = 10.69*1.6*1000/(60*60) = 4.75 m/s4.75 = s/ts = 4. 1we also have acceleration = 2.18 m/s², initial velocity = 0 m/sso it will take   4.36 seconds to reach her average velocity 10.69 miles/hour.

Answer (d) the universe had cooled enough for atoms to combine, protons and neutrons were too far apart to form nuclei;