Derive the formula to find the focal length of concave mirror and convex lens?
Answers
Answer:
1)focal length for concave mirror = R/2
here R is radius
2)focal length for convex lens=1/P
here P is power
if we have to find out the focal length in cm then we have to use the formula=100/P for focal length of convex lens
Answer:
Focal Length of Concave Mirror Formula
Explanation:
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Determination of Focal Length of Concave Mirror and Convex Mirror
Physics
Determination of Focal Length ...
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What are Convex and Concave Mirrors?
A curved mirror in which a reflective surface bulges out towards the light source is known as convex mirror. The convex mirror reflects the light outwards and so it is not used to focus light. As the object comes nearer to the mirror, the size of the object gets larger until it reaches its original size. These mirrors are also known as the diverging mirrors.
A concave mirror has a reflecting surface that caves inwards. The mirror also converges the light at one prime focus point; hence they are also called as converging mirrors. They are applied to focus light. Depending upon the location of the object with respect to the mirror, the size of the image formed by the concave mirror varies. It can be real or virtual, inverted or erect and magnified, reduced, or be similar in size of the object depending upon the position.
Focal Length of Concave Mirror
This article will help you find the focal length of a concave mirror. Let’s look at the theory to obtain the image of a farther object.
Like a plane mirror, the concave mirror obeys the law of reflection of light.
Ray of light from an object – The rays of light emitted from a distant object, e.g., distant buildings or sun, are parallel to each other. When the parallel rays from the source fall on the concave mirror along the axis, reflect and meet at the point in front of the mirror, which is known as the mirror's principal focus.
At the focus of the mirror, a real, inverted, and very small image size is formed.
Focal length – Focal length of the concave mirror is the distance between the pole P of concave mirror and the focus F. By obtaining the Real image of the distant object, the focal length of concave mirror can be determined, as shown in the diagram.
Focal Length of Concave Mirror Formula
Lets see the above shown diagram,
Focal Length – The space between the pole P of concave mirror and the focus F is the focal length of concave mirror. By obtaining the Real image of a distant object at its focus, the focal length of the concave mirror can be estimated as shown in the diagram.
The focal length of the convex mirror is positive, whereas that of the concave mirror is negative. The same can also be proved by using the mirror formula
Let's see how
Since we know that an object is always placed at the left side or direction opposite the incidence ray of the mirror, the object distance will always be negative.
u = -u
v = -v (Image distance is negative since image produced by concave mirrors are usually on the left side or direction opposite to the incidence ray)
Using mirror formula,
1/f = 1/v +1/u
Or, 1/f = (-u-v)/uv
Or, f = -uv/(u+v)
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