# Distance between light source and slits in the double slit

• sqljunkey
In summary, the distance between the light source and the slits does matter in determining the interference pattern. Collimation of light changes with distance, affecting the pattern, and the further the light source, the more impurities can interfere with the pattern. A coherent source and a lens system can help ensure a good interference pattern, while using a laser source can also produce a good pattern due to its monochromatic wave.

#### sqljunkey

Hi,

Does the distance between the light source and the slits matter? Does the interference pattern change if you move the light source closer or further from the slits?

I read from this link that the collimation of the light changes with distance and that affects the interference pattern, and also the further the light source is the more impurities there will be between the light source and the slits and that will interfere with the pattern we see.

https://physics.stackexchange.com/q...ght-and-distance-between-the-slits-is-changed

sqljunkey said:
Does the distance between the light source and the slits matter?
Yes. The simple formula assumes that the two sources are totally coherent. That means the optical path from the (Infinitely narrow) source slit is equal for the two slits (and across them). One way to ensure this is to have the source at great distance behind. Alternatively, a lens system can be used.
Using a laser source takes care of that and it also gives a good monochromatic wave which produces a good pattern.

## 1. What is the double slit experiment?

The double slit experiment is a classic physics experiment that demonstrates the wave-like nature of light. It involves shining a beam of light through two narrow slits and observing the resulting interference pattern on a screen behind the slits.

## 2. How does the distance between the light source and slits affect the interference pattern?

The distance between the light source and the slits affects the spacing of the interference pattern on the screen. As the distance increases, the pattern becomes more spread out and the bright fringes become narrower. As the distance decreases, the pattern becomes more compact and the bright fringes become wider.

## 3. What happens to the interference pattern if the distance between the light source and slits is increased?

If the distance between the light source and slits is increased, the interference pattern will become more spread out and the intensity of the bright fringes will decrease. This is because the light waves have more time to spread out and overlap with each other, resulting in a decrease in the overall intensity of the pattern.

## 4. How does the distance between the light source and slits affect the wavelength of light?

The distance between the light source and slits does not affect the wavelength of light. The wavelength of light is determined by the source itself and is not affected by the distance it travels.

## 5. Can the distance between the light source and slits be changed during the experiment?

Yes, the distance between the light source and slits can be changed during the experiment. This can be done by moving either the light source or the slits, as long as the position of the screen remains constant. However, changing the distance during the experiment may affect the overall results, so it is important to keep this variable constant for accurate measurements.