The first figure in the attached file shows that over 50% of the radiation reach

Question

The first figure in the attached file shows that over 50% of the radiation reaching earth from the Sun is long-wavelength infrared radiation which we perceive as heat, not light. Thin film coatings on windows serve two purposes. (1) On warm days, the coatings reflect almost all of the infrared radiation while allowing almost all of the visible light through the window (the glass absorbs most of the ultraviolet.) The rooms inside stay cooler and require less air conditioning. (2) On cold days, the same thin film coating allows visible light to enter the room and reflects the thermal infrared radiation from the interior back into the room, keeping it warm. The reflectance of the thin film window coating as a function of wavelength is shown in the second figure posted with this assignment.

(Please briefly explain the answer of each question.)

1.Which are benefits of thin-film coatings on windows?

A.The keep ultraviolet light out of the house in the summer and winter.

B.They keep infrared radiation out of the house in the summer.

C.They keep infrared radiation inside the house during the winter.

D.b and c

E.a, b and c

2. A 1.25 refractive index thin film on a 1.50 refractive index glass window is made to reflect infrared radiation of wavelength 1000 nm. What is the net reflective phase change of infrared radiation reflected off the front surface of the thin film relative to the radiation reflected off the back surface of the film and returning to the front?

A.Zero

B.1/4 wavelength

C.1/2 wavelength

D.None of the above

3. A 1.25 refractive index thin film on a 1.50 refractive index glass window is made to reflect infrared radiation of wavelength 1000 nm. Which wavelength below is closest to the wavelength of the infrared radiation in while in the thin film?

A.670 nm

B.800 nm

C.1000 nm

D.1250 nm

E.1500 nm

4. The actual thin film built for windows reflects about what percent of the incident infrared radiation at 1000 nm?

A.10

B.30

C.50

D.70

E.90

Explanation / Answer

Ans part a

option a,b,c are correct so answer is option E

Part-b

phase change =wavelength/2

Part-c

closest wavelength is 1250nm

Part-d

from second figure percentage of infrared radiation = 70%

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