Lenses homework problem

In summary, the formula for calculating the focal length of a lens is F = (n2 - n1) / (n1 * R). The power of a lens can be determined using the formula P = 1 / F. A convex lens converges light rays at a focal point while a concave lens causes light rays to diverge. The thickness of a lens affects its focal length, with thicker lenses having a shorter focal length. The magnification of a lens can be calculated by dividing the image distance by the object distance using the formula m = di / do.
  • #1
no idea
93
0
An object pin is placed 20cm in front of a convex lens which is 10 cm away from a plane mirror . An inverted image is found at the same position of the object(above the object).
What is the focal length?
thanks
 
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  • #2
Here are a few hints. Is the image formed by the lens real or virtual? What does a plane mirror do?

Figure out where the image would be if the mirror wasn't there.
 
  • #3


The focal length can be calculated using the lens equation, which states that 1/f = 1/do + 1/di, where f is the focal length, do is the distance of the object from the lens, and di is the distance of the image from the lens. In this case, do = 20cm and di = 20cm, since the image is found at the same position as the object. Plugging these values into the lens equation, we get: 1/f = 1/20cm + 1/20cm = 2/20cm. Solving for f, we get a focal length of 10cm. This means that the convex lens has a focal length of 10cm, and it is able to create an inverted image at the same position as the object when placed 20cm in front of it. I hope this helps!
 

1. What is the formula for calculating the focal length of a lens?

The formula for calculating the focal length of a lens is F = (n2 - n1) / (n1 * R), where F is the focal length, n1 is the refractive index of the medium the light is coming from, n2 is the refractive index of the medium the light is entering into, and R is the radius of curvature of the lens.

2. How do you determine the power of a lens?

The power of a lens can be determined by using the formula P = 1 / F, where P is the power of the lens and F is the focal length of the lens.

3. What is the difference between a convex and concave lens?

A convex lens is thicker in the middle and thinner at the edges, causing light rays to converge at a focal point. A concave lens is thinner in the middle and thicker at the edges, causing light rays to diverge.

4. How does the thickness of a lens affect its focal length?

The thicker the lens, the shorter the focal length will be. This is because a thicker lens has a smaller radius of curvature, which leads to a shorter focal length.

5. How do you calculate the magnification of a lens?

The magnification of a lens can be calculated by dividing the image distance by the object distance. This is represented by the formula m = di / do, where m is the magnification, di is the image distance, and do is the object distance.

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