The drawing shows a cross section of a plano-concave lens resting on a flat glass plate. (A plano-concave lens has one surface that is a plane and the other that is concave spherical.) The thickness t is 1.38 10-5 m. The lens is illuminated with monochromatic light (λvacuum = 535 nm), and a series of concentric bright and dark rings is formed, much like Newton's rings. How many bright rings are there?

I have been using the equation t=n(lambda)/2.... but it says im wrong. help?

To determine the number of bright rings formed by a plano-concave lens, you need to use a different formula known as the equation of Newton's rings:

t = (m + 1/2)(λn)/2

In this equation:
- t represents the thickness of the air film between the plano-concave lens and the flat glass plate,
- m represents the order of the bright ring,
- λn represents the wavelength of the monochromatic light in the given medium.

In this case, the thickness t is given as 1.38 × 10^(-5) m, and the wavelength λvacuum is given as 535 nm. However, keep in mind that the given wavelength is in vacuum, but you need the wavelength in the medium where the light is passing through.

To find the wavelength in the medium, you can use the formula:

λmedium = λvacuum/n

Where n represents the refractive index of the medium.

Since the medium is air in this case, the refractive index of air is approximately 1 (to a good approximation). Therefore, the wavelength in the medium is the same as in a vacuum, so:

λmedium = λvacuum = 535 nm

Now, substitute the values in the equation of Newton's rings:

t = (m + 1/2)(λn)/2

1.38 × 10^(-5) m = (m + 1/2)(535 × 10^(-9) m)/2

Solving this equation for m will give you the order of the bright ring. Since m must be a positive integer, you can start with m = 0 and increment it until you reach the maximum possible value.

By trying different values of m, you can find the number of bright rings formed by the plano-concave lens.

just keep thinking you can figure it out it is a college course so i cant help you.