What is the minimum thickness of a soap film that appears dark in reflected ligh
Practice Questions
Q1
What is the minimum thickness of a soap film that appears dark in reflected light for a wavelength of 600 nm?
150 nm
300 nm
600 nm
1200 nm
Questions & Step-by-Step Solutions
What is the minimum thickness of a soap film that appears dark in reflected light for a wavelength of 600 nm?
Correct Answer: 200 nm
Step 1: Understand that we are looking for the minimum thickness of a soap film that appears dark when light reflects off it.
Step 2: Know that for a soap film, dark appearance in reflected light happens due to destructive interference.
Step 3: Remember the formula for destructive interference in reflected light: t = λ / (2n), where t is the thickness, λ is the wavelength of light, and n is the refractive index.
Step 4: Identify the given values: the wavelength λ is 600 nm and the refractive index n for soap is approximately 1.5.
Step 5: Plug the values into the formula: t = 600 nm / (2 * 1.5).
Step 6: Calculate the denominator: 2 * 1.5 = 3.
Step 7: Divide the wavelength by the denominator: 600 nm / 3 = 200 nm.
Step 8: Conclude that the minimum thickness of the soap film that appears dark in reflected light is 200 nm.
