Thomas Young is generally credited for conduction the double slit experiment which shows evidence for wave nature of light through interference
The two slit interference can be investigated as follows:
- We would need a monochromatic(consists of only one frequency) light source, for example lasers.
- We set up the experiment such that the laser passes through two very thin adjacent slits.
- We record the the pattern formed on a screen
- When the light beams from the two slits interfere constructively, it forms a bright fringe on the optical screen.
- When the light beams from the two slits interfere destructively, it forms a dark fringe on the optical screen.
To understand the interference taking place in double slit experiment, let’s look at the following diagram :
- The distance between the two slits is d
- The two rays r1 and r2 , meet at P1 on the optical screen
- The angular displacement of the point P1 is θ
- If we consider the distance from the slits to optical screen >> d , then we can consider the rays r1 and r2 to be almost parallel
- Then the path difference (extra distance travelled) between the two rays is : d x sin θ
- For constructive interference , the path difference must be an integer multiple of the wavelength
- i.e. , where m = 0, 1, 2, 3, 4, . . . . . .
- For destructive interference , the path difference must be
- i.e. , where m = 0, 1, 2, 3, 4, . . . . .
Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)