The glass panels of a sky roof need to be coated in order to screen out ultraviolet radiation (10-400 nm wavelength) but without color distortion in the visible spectrum. Candidate coating materials are gallium nitride (GaN) with a band gap,Eg, of 3.2 eV, or gallium arsenide (GaAs) with a band gap, Eg, of 1.34 eV. Choose the best explanation for which of these materials, if either, will work.

DATA: representative wavelengths associated with different colors in the visible spectrum:
violet 425 nm
blue 475 nm
green 535 nm
yellow 590 nm
orange 610 nm
red 700 nm

I)GaAs is the best choice, it has a band gap low enough to block out UV radiation while allowing visible light to pass.

II)GaN is the best choice, it has a band gap low enough to block out UV radiation while allowing visible light to pass.

III)Neither will work, due to the electromagnetic spectrum any material that blocks out UV radiation will also block out visible light, this is why sunscreen and sunglasses tend to be somewhat opaque.

IV)Neither will work, UV light will be able to pass through both of them if visible light is able to pass through as well.

V)Neither will work, visible light has energy greater than 3 eV and the semiconductors will be opaque.

VI)Both will work, visible light has energy lower than 1 eV and is able to pass through both materials unaltered.

I is wrong answer

Someone please answer this ;(

I agree I) is wrong

I got green with IV

IV)Wrong !Neither will work, UV light will be able to pass through both of them if visible light is able to pass through as well.

Got it wrong for IV), hmm wonder why folks are messing with the answers.

The correct answer is II

Thank you Anonymous and Anonima

To determine which material would be the best choice for coating the sky roof panels, we need to consider their band gap energies and the representative wavelengths of different colors in the visible spectrum.

The band gap energy of a material determines the minimum energy required for an electron to move from the valence band to the conduction band, allowing the material to absorb light. If the band gap energy is lower than the energy of a specific wavelength of light, that light will be absorbed by the material.

Looking at the candidate materials, GaN has a band gap energy (Eg) of 3.2 eV, while GaAs has a band gap energy of 1.34 eV.

Now, let's compare the band gap energies with the representative wavelengths of different colors in the visible spectrum:

- Violet light has a wavelength of 425 nm, which corresponds to an energy of approximately 2.92 eV.
- Blue light has a wavelength of 475 nm, which corresponds to an energy of approximately 2.61 eV.
- Green light has a wavelength of 535 nm, which corresponds to an energy of approximately 2.32 eV.
- Yellow light has a wavelength of 590 nm, which corresponds to an energy of approximately 2.10 eV.
- Orange light has a wavelength of 610 nm, which corresponds to an energy of approximately 2.03 eV.
- Red light has a wavelength of 700 nm, which corresponds to an energy of approximately 1.77 eV.

Based on this information, we can see that both GaN and GaAs have band gap energies higher than the energy of all the representative visible light wavelengths. This means that both materials would allow visible light to pass through without significant absorption or color distortion.

However, we are specifically looking for a material that can block out ultraviolet (UV) radiation (10-400 nm wavelength) while allowing visible light to pass through.

Since GaN has a higher band gap energy (3.2 eV) compared to GaAs (1.34 eV), it means that GaN has a wider band gap and therefore requires more energy to absorb light. This makes GaN a better candidate for blocking UV radiation while still allowing most visible light to pass through.

Therefore, the best explanation would be II) GaN is the best choice, as it has a band gap low enough to block out UV radiation while allowing visible light to pass without significant absorption or color distortion.