Question

Two colors of light, green and yellow, undergoes diffraction through the same diffraction grating. Which color of light sees greater diffraction angle?

		Both colors undergo the same diffraction angle.
		Green
		Yellow We will measure the spectra of helium, mercury and neon gas discharge tubes. True False

Light is emitted when a valence electron moves from a lower state to an excited state.

True

False

Light produced from spontaneous emission is incoherent.

True

False

Answer 1

Solution:

Part (a) For the diffraction grating, maxima is given by

d*sinθ = mλ

Thus we see that λ = wavelength of light is proportional to the diffraction angle θ.

Since yellow light has larger wavelength (570-590 nm) than the green light (495-570 nm), the yellow light sees greater diffraction angle.

Part(b) True/False

(1) Q: Light is emitted when a valence electron moves from a lower state to an excited state.

Answer: An electron in an excited state has more energy than in the lower state. Thus when a valence electron moves from excited state to lower state, its excess energy is given off as light photon.

Thus statement in the question is FALSE.

(2) Q: Light produced from spontaneous emission is incoherent.

Answer: In spontaneous emission many atoms (that is valance electrons of many atoms) go to lower state from excited state. Neither an excited states are fixed nor the lower states are fixed. Thus electrons from different atoms gives off different amount of energy as light of different color. Also, there is no phase relation between light waves.

Hence statement in the question is TRUE