Well, if you think about a single ray of light hitting the mirror, it only hits a very very small spot. And if we think of each little spot on the mirror as being basically flat, then each ray of light that hits the mirror acts like it's hitting a flat mirror. When we draw light rays on a piece of paper, we usually use something called a 'tangent line'. This is just a straight line, drawn right up against the curve of the mirror. A tangent line is kind of like what the curve would look like really really close up.
Convex mirrors cause light to spread out, concave mirrors cause light to go in and create a focal point. But lenses work the opposite way: concave lenses spread the light out, convex lenses focus the light. Why don't they work in the SAME way as mirrors, instead of the opposite way? Dana, Thanks for your question.
The reason that mirrors and lenses behave so differently is that light passes though lenses but bounces off mirrors. But when light rays strike a convex mirror, the reflected rays spread out. Like flat mirrors, convex mirrors also produce images which are virtual, upright, front-back inverted, and laterally inverted. An obvious difference though is that the images are smaller than the objects are in real life. The outwards curve of the convex mirror also results in a wider so-called field of view.
In the convex mirror, we can see a large part of the landscape because everything is shrunk down in size, whereas in the flat mirror, we can only see the tops of a few trees.
For this reason, convex mirrors are used as safety mirrors wherever you might need a larger field of view. Some are used to allow drivers coming out of a driveway to see any pedestrians on the footpath before the car reaches the footpath. Convex mirrors are also used in carparks, in hospital corridors, offices, shops, at train stations, and many, many other places. Convex mirrors are often used in side-view mirrors on cars, because they allow you to see a wider view of the road behind you.
In the flat mirror of this minibus, you can see only one person. In the convex mirror though, you can see six people. When driving, the convex mirror gives you a wider view of the road. Many, if not most, trucks, vans, and buses have, on both the driver side and the non-driver side, both flat mirrors and convex mirrors. We can use ray diagrams to work out why convex mirrors produce diminished images. Now because the image is smaller, everything seems to be further away, but in fact this is just an illusion.
As you can see from the ray diagram, the image of the racket is a shorter distance behind the mirror than the actual racket is in front of the mirror. Concave mirrors are mirrors which curve inwards. So it should be easy to remember which is a concave mirror and which is a convex mirror. Unlike convex mirrors which reflect parallel light rays outwards, concave mirrors reflect parallel light rays inwards towards a focus. The distance of this focal point to the so-called vertex of the mirror is called the focal length.
Concave mirrors produce two types of images depending on how far the object is from the mirror. So-called shaving mirrors are concave mirrors. Make up mirrors are also concave. Dentists sometimes use concave mirrors to see a magnified image of your teeth. This type of image is called a real image because you can project it onto a screen. The light rays coming from the scene all reflect in such a way that the light is focused on the same side of the mirror as the object, but the image is upside down, and, in this case diminished, that is smaller than the object.
Placing a screen of some sort at this position will allow you to see the image on the screen, because reflected light is illuminating the screen. Many astronomical telescopes, especially the bigger ones, use large concave mirrors, and smaller secondary mirrors, to capture light from distant stars and planets and to then focus it onto cameras which can then take pictures.
Because they use mirrors, these kinds of telescopes are called reflecting telescopes. Now, not all telescopes use mirrors. Many use lenses. In the next section of Lesson 3 , these two rules will be applied to determine the location, orientation, size and type of image produced by a concave mirror.
As the rules are applied in the construction of ray diagrams, do not forget the fact that the law of reflection holds for each of these rays. It just so happens that when the law of reflection is applied for a ray either traveling parallel to the principal axis or passing through F that strikes the mirror at a location near the principal axis, the ray will reflect in close approximation with the above two rules.
Physics Tutorial. My Cart Subscription Selection. Student Extras. The two types of spherical mirrors are shown in the diagram on the right. Spherical mirrors can be thought of as a portion of a sphere that was sliced away and then silvered on one of the sides to form a reflecting surface. Concave mirrors were silvered on the inside of the sphere and convex mirrors were silvered on the outside of the sphere.
In Lesson 3 we will focus on concave mirrors and in Lesson 4 we will focus on convex mirrors. Beginning a study of spherical mirrors demands that you first become acquainted with some terminology that will be periodically used.
The internalized understanding of the following terms will be essential during Lessons 3 and 4. If a concave mirror were thought of as being a slice of a sphere, then there would be a line passing through the center of the sphere and attaching to the mirror in the exact center of the mirror.
This line is known as the principal axis. The point in the center of the sphere from which the mirror was sliced is known as the center of curvature and is denoted by the letter C in the diagram below. The point on the mirror's surface where the principal axis meets the mirror is known as the vertex and is denoted by the letter A in the diagram below. The vertex is the geometric center of the mirror. Midway between the vertex and the center of curvature is a point known as the focal point ; the focal point is denoted by the letter F in the diagram below.
The distance from the vertex to the center of curvature is known as the radius of curvature represented by R.
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