62) This question goes over Young's double-slit experiment and asks us which answer choice(s) will decrease the spacing between bright regions.
The distance between bright fringes can be expressed with the following equation.
Choice A: By using a shorter wavelength, λ is decreased. For example, let's say that the wavelength λ is halved.
When the wavelength is halved, the distance between bright regions would be halved as well. Choice A is valid.
Choice B: Let's take an example where the distance from the slits to the screen is halved.
When the distance from the slits to the screen is halved, the distance between bright regions must be halved, in order to balance the equation. Choice B must be valid as well.
Choice C: Again let's take an example where we double the distance between the slits.
This shows us that if the distance between the slits is doubled, the distance between bright regions would be halved. Therefore, Choice C must also be valid.
Choice D: If we perform the experiment underwater, the speed of light will be slower due to the change to a denser medium. Using the wave equation v = f * λ we know that when the velocity decreases, so will the wavelength. As shown in the explanation of choice A, a shorter wavelength leads to a shorter distance between fringes. Choice D is valid.
All the choices will decrease the distance between the bright regions, so our answer is Choice E.
Answer: E
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