the energy does not change the energy is not proportional to the frequency the e

Question

the energy does not change

the energy is not proportional to the frequency

the energy is inversely proportional to the frequency

the energy goes up

the energy is proportional to the frequency

the energy goes down

(a) Calculate the wavelength of light in vacuum that has a frequency of 9.8 X 10^10 Hz. m (b) What is its wavelength in benzene? (The index of refraction of benzene is 1.501.) m (c) Calculate the energy of one photon of such light in vacuum. Express the answer in electron volts. eV (d) What is the properties of and effect on the energy of the photon when it enters the benzene? (Select all that apply.) the energy does not change the energy is not proportional to the frequency the energy is inversely proportional to the frequency the energy goes up the energy is proportional to the frequency the energy goes down

Explanation / Answer

1.

frequency * wavelength = c (speed of light)

We know c=3 * 108 m/s

Thus wavelength = c/frequency = 3 *108 / (9.8*1010 )

or, wavelength = 0.31 * 10-2 m = 3.1*10-3 m

(b)

index of refraction: n = 1.501

wavelength in a medium = wavelength in vacuum * n

from above ques wavelength in vacuum: 3.1*10-3 m

Thus,

wavelength in benzene = 3.1*10-3 m * 1.501 = 4.65 * 10-3 m

(c)

Energy of 1 photon in vacum:

E = h * f

h = planck's constant: 6.63 * 10-34 kg/s

f = 9.8*1010 Hz

Thus,

E=6.63 * 10-34 * 9.8*1010 = 6.5 * 10-23 J

To convert to eV divide by e = 1.6 * 10-19

E = 6.5 * 10-23 /1.6 * 10-19   = 4.1 * 10-4 eV

(d) What is the properties of and effect on the energy of the photon when it enters the benzene? (Select all that apply.)

the energy does not change : True

the energy is not proportional to the frequency : False

the energy is inversely proportional to the frequency : False

the energy goes up: False

the energy is proportional to the frequency : True

the energy goes down: False

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