Question

If a spherical mirror is immersed in water, does its focal length change?

Asked by: Amanda

Answer

Mirrors, spherical or otherwise, operate on the principle that the angle of reflection of a ray of light equals the angle at which it strikes the mirror's surface. That behavior is not affected by the medium in which the light travels, so the mirror's focal length would be no different in air or water.

If you had asked about the focal length of a LENS, however, the answer would be different. Lenses work by REFRACTION, not reflection, and the angle of refraction is based on the difference between the speed of light in the lens compared to the surrounding medium. When immersed in water, the difference between light's speed in the lens and the surrounding medium is less than the difference when it's in air, and the focal length of a lens would be greater under water.

Answered by: Paul Walorski, Part Time Physics Instructor

Search

Loading



Sponsors

USC University of Southern California Dornsife College Physics and Astronomy Department McMaster University Physics and Astronomy Department

Science Quote

'There comes a time when the mind takes a higher plane of knowledge but can never prove how it got there. All great discoveries have involved such a leap. The important thing is not to stop questioning.'

Albert Einstein
(1879-1955)

Deal of the Day

Image of Shark Tooth Fossil in Matrix. Click on this image for more info. Shark Tooth Fossil in Matrix
Regular Price: $39.95
Today's Price: $15.00
Superb shark fossil specimen for the science classroom! Buy it now! Deal ends at midnight!

Top Selling

Here are our physics & astronomy bestsellers:
Mini Plasma Ball
Slide Making Kit
Top Secret - Spinning Top
Wood Grain Newtons Cradle
Deluxe 3D Mirascope
Solar Radiometer
Periscope
Solar Science 4M Kit
Ultimate Chemistry Set CHEM C3000
3D Magnetic Field Tube