Ch. 26 Flashcards
(5 cards)
What is the radius of curvature of a plane mirror? What is the focal
Length? Explain.
The radius of curvature of a plane mirror is infinite because the plane mirror is a flat mirror. If the radius is infinite then the focal length is also infinite.
We know that f = R/2, so if R is infinite then so is f
Dish receivers for satellite TV always use the concave side of the dish never the convex. Explain.
The dish acts as a mirror due to the painting on it. If we use the convex side of the dish, the parallel rays would be diverted outward. If we use the concave side of the dish it converges all the parallel rays to its focus. Therefore using the concave side results in more intense rays to the receiver placed st the focus of the dish.
Suppose you would like to start a fire by focusing sunlight into a piece of paper. In conceptual example 26-4 we saw that a concave mirror would be better than a convex mirror for this purpose. At what distance from the mirror should be held for the best results?
Concave mirror is preferred over the convex because when the light rays strike a concave mirror it gets reflected and meets at the focal point of the mirror. Whereas, the reflected rays from a convex mirror diverge from the mirror and appear as they come from the focal point behind the mirror.
The parallel rays from the sun are focused on a very small area of the paper. If a concave mirror is used the light rays will be converged in front of the mirror. Whereas, when the rays are focused on a convex mirror the light rays appear to come from the focal point behind the mirror. A concave mirror focuses the light rays more strongly on the paper when compared to a convex mirror.
Best results are when the paper is held at the focal length of the concave mirror, with the light rays converging on a small area of the paper resulting in the greatest heat.
When light propagates from one medium to another, does it always bend toward the normal. Explain.
No, the bending of light depends upon the speed through the medium.
The light bends towards the normal when the light enters a medium in which it’s speed of propagation is lower than it was in the first medium.
The light bends away from the normal when it enters a medium in which it’s speed of propagation is greater than the first medium.
A swimmer at point B in figure 26-55 needs help. Two lifeguards depart simultaneously from their tower but they…
Even though the two life guards are running and swimming at the same speeds, they can run much quicker in sand than water. In the ACB path the sand part is longer and therefore he swims less and reaches point B earlier.
