Peoples Physics Book Version-2

17.1. The Big Idea http://www.ck12.org

Double slit interference maxima.mis the order of the interference maximum in question,dis the distance between
slits. andθis the angular position of the maximum.

mλ=dsinθ

Single slit interference maxima.mandθare defined as above anddis the width of the slit.

mλ=dsinθ

Diffraction grating interference maxima.mandθare defined as above anddis the distance between the lines on the
grating.

mλ= 2 nd

Thin film interference:nis the index of refraction of the film,dis the thickness of the film, andmis an integer.
In the film interference, there is aλ/2 delay (phase change) if the light is reflected from an object with an index of
refraction greater than that of the incident material.

1

f

=

1

d 0

+

1

di

For lenses, the distance from the center of the lens to the focus isf. Focal lengths for foci behind the lens are positive
in sign. The distance from the center of the lens to the object in question isd 0 , where distances to the left of the
lens are positive in sign. The distance from the center of the lens to the image isdi. This number is positive for real
images (formed to the right of the lens), and negative for virtual images (formed to the left of the lens). For mirrors,
the same equation holds! However, the object and image distances are both positive for real images formed to the
left of the mirror. For virtual images formed to the right of the mirror, the image distance is negative

M=

−di

d 0

The size of an object’s image is larger (or smaller) than the object itself by its magnification,M. The level of
magnification is proportional to the ratio ofdianddo. An image that is double the size of the object would have
magnificationM=2.

R= 2 f

The radius of curvature of a mirror is twice its focal length