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Explain why the focal length of a plane mirror is infinite, and explain what it means for the focal point to be at infinity.

Short Answer

Expert verified

The focal length of a plane mirror is because the parallel rays couldn’t be focused hence f is infinity.

Step by step solution

01

Radius of curvature for a flat mirror

Now, we know that the focal length of any mirror is equal to the half of the radius of curvature of the mirror:

f=R2

Since we know that the flat mirror doesn’t have a curvature meaning that the radius of curvature of such mirror is equal to infinity. Hence if we replaceR= , putting this in the above equation we get:

f=2=

02

Conclusion

All light rays are parallel to the main optical axis of the mirror and are reflected from the surface of the mirror through the focal point. Since the focal point of the plane mirror is in infinity, meaning that the rays which are parallel to the main optical axis are reflected back to the parallel to the main optical axis.

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Most popular questions from this chapter

The laws of optics also apply to electromagnetic waves invisible to the eye. A satellite TV dish is used to detect radio waves coming from orbiting satellites. Why is a curved reflecting surface (a “dish”) used? The dish is always concave, never convex; why? The actual radio receiver is placed on an arm and suspended in front of the dish. How far in front of the dish should it be placed?

When a converging lens is immersed in water, does itsfocal length increase or decrease in comparison with the value inair? Explain.

A person is lying on a diving board 3.00 m above the surface of the water in a swimming pool. She looks at a penny that is on the bottom of the pool directly below her. To her, the penny appears to be a distance of 7.00 m from her. What is the depth of the water at this point?

A Spherical Fish Bowl. A small tropical fish is at the centre of a water-filled, spherical fish bowl 28.0 cm in diameter.
(a) Find the apparent position and magnification of the fish to an observer outside the bowl. The effect of the thin walls of the bowl may be ignored. (b) A friend advised the owner of the bowl to keep it out of direct sunlight to avoid blinding the fish, which might swim into the focal point of the parallel rays from the sun. Is the focal point actually within the bowl?

A student claims that she can start a fire on a sunny day using just the sun’s rays and a concave mirror. How is this done? Is the concept of image relevant? Can she do the same thing with a convex mirror? Explain.

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