Q. In a thin film of oil on water, if the thickness of the film is 0.1 mm and the wavelength of light in air is 600 nm, what is the condition for constructive interference?
A.2t = (m + 0.5)λ
B.2t = mλ
C.2t = (m + 1)λ
D.2t = mλ/2
Solution
For constructive interference in a thin film with a denser medium below, the condition is 2t = mλ.
Q. In a thin film of oil on water, if the thickness of the oil film is 0.5 μm and the wavelength of light in air is 600 nm, what is the wavelength of light in the oil?
A.400 nm
B.500 nm
C.600 nm
D.700 nm
Solution
Wavelength in oil = λ/n, where n is the refractive index of oil. Assuming n = 1.5, λ_oil = 600 nm / 1.5 = 400 nm.
Q. In a thin film of oil on water, which color of light will be most prominently reflected if the film thickness is such that it causes constructive interference?
A.Red
B.Green
C.Blue
D.Yellow
Solution
The color that is most prominently reflected depends on the thickness of the film and the wavelength of light. Typically, shorter wavelengths (like blue) are more affected by thin films.
Q. In a thin film of oil on water, which color will appear at the center of the pattern if the film thickness is such that the path difference is λ?
A.Red
B.Blue
C.Green
D.Yellow
Solution
At the center, where the path difference is λ, constructive interference occurs, and the color that appears depends on the wavelength of light, typically red for thin films.
Q. In a thin film of oil on water, which color will appear at the topmost layer if the film is of thickness comparable to the wavelength of blue light?
A.Red
B.Green
C.Blue
D.Yellow
Solution
The color that appears depends on the thickness of the film and the wavelength of light. Blue light has a shorter wavelength and will be more prominently reflected.
Q. In a thin film of oil on water, which color will appear at the topmost layer if the film thickness is such that it causes constructive interference for blue light?
A.Red
B.Green
C.Blue
D.Yellow
Solution
If the film thickness causes constructive interference for blue light, blue will be the color that appears at the topmost layer.
Q. In a thin film of oil on water, which color will appear at the topmost layer if the thickness of the film is such that it causes constructive interference for blue light?
A.Red
B.Green
C.Blue
D.Yellow
Solution
If the film thickness causes constructive interference for blue light, blue will be the color that appears most prominently.
Q. In a thin film of oil on water, which color will appear at the topmost layer when viewed from above?
A.Red
B.Blue
C.Green
D.Yellow
Solution
The color that appears depends on the thickness of the film and the wavelength of light. Typically, red light is least affected by thin film interference.
Q. In a thin film of soap, why do we see different colors?
A.Different wavelengths interfere constructively at different angles
B.Different wavelengths are absorbed
C.Different wavelengths reflect differently
D.Different wavelengths travel at different speeds
Solution
Different colors are seen because different wavelengths of light interfere constructively at different angles due to the varying thickness of the soap film.
Correct Answer: A — Different wavelengths interfere constructively at different angles