Question

What is the minimum (non-zero) thickness of a benzene (n = 1.501) thin film that will result in constructive interference when viewed at normal incidence and illuminated with orange light (λvacuum = 615 nm)? A glass slide (ng = 1.620) supports the thin film.

Answer 1

Step-by-step explanation:

At each reflecting surface (benzene and glass) there will be 180 degree phase change.

Now, for constructive interference the optical path in benzene is
`\lambda`.

Formula to calculate thickness of a benzene thin film is as follows.

Optical path length through benzene (
`\lambda`) =
`2 * n * d`

Hence, substituting the given values into the above formula as follows.

Optical path length through benzene =
`2 * n * d`

d =
`\frac{\text{Optical path length through benzene}}{2 * n}`

=
`(\lambda)/(2 * n)`

=
`(615 * 10^(-9))/(2 * 1.501)` (as 1 nm =
`10^(-9)m`

= 204.9 m

Thus, we can conclude that minimum thickness of benzene is 204.9 m.