The path difference between two interfering light waves meeting at a point on the screen is…
The path difference between two interfering light waves meeting at a point on the screen is $\left(\frac{57}{2}\right) \lambda$. The band obtained at that point is
$29^{\text {th }}$ bright band
$57^{\text {th }}$ dark band
$57^{\text {th }}$ bright band
$29^{\text {th }}$ dark band
Solution
Path difference $=\frac{57}{2} \lambda=28.5 \lambda$
Since the path difference is not an integral multiple of $\lambda$, it is not a bright bond.
Path difference for $n$th dark band is given by $\left(n-\frac{1}{2}\right) \lambda$
Hence $\mathrm{n}=29$.