When the object is placed at the focus of concave lens the image formed is virtual and inverted?

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When viewing an object through a convex lens, the observer will always see an upright, smaller version, for all positions of the object.

This can be demonstrated as follows.

Object at more than `2F`

This means that the object is further away than two principal focal lengths from the concave lens.

The image is smaller, upright, virtual and between the principal focal point on the object side and the concave lens.

Object at `2F`

When the object is at two principal focal points from the concave lens, you get the following ray diagram:

The image is smaller, upright, virtual and between the principal focal point on the object side and concave lens.

Object between `2F` and `F`

Placing the object between two focal points and one focal point produces the following ray diagram:

The image is smaller, upright, virtual and between the principal focal point on the object side and the concave lens.

Object at `F`

When the object is placed at the focal point of the concave lens, you get the following ray diagram:

The image is smaller, upright, virtual and between the principal focal point on the object side and the concave lens.

Object between `F` and concave lens

When the object is placed between the principal focal point and the lens, the following occurs:

The image is smaller, upright, virtual and between the principal focal point on the object side and the concave lens.

Conclusion

We can see from the above that for every position of the object the image created is always.

SMALLER

UPRIGHT

VIRTUAL (can not be projected on a screen)

Between principal focal point and the concave lens

All images through a concave lens will look smaller and closer.

A tank is filled with water to a height of 12.5 cm. The apparent depth of a needle lying at the bottom of the tank is measured by a microscope to be 9.4 cm. What is the refractive index of water? If water is replaced by a liquid of refractive index 1.63 up to the same height, by what distance would the mircoscope have to be moved to focus on the needle again?

Case I: When tank is filled with water. Given, real depth = 12.5 cm;           apparent depth = 9.4 cm Now, using the formula, 

                    μ = real depthapparent depth

Refractive index,  μ = 12.59.4 = 1.33

Case II: When water in the tank is replaced by another liquid.

apparent depth = real depthμ 

i.e., apparent depth = 12.51.63 = 7.67 cm

Distance through which microscope has to be moved downward is = (9.4 – 7.67) cm = 1.73 cm.

The word "lens" owes its origin to the Latin word for lentils, the tiny beans that have from ancient times been an important ingredient in the cuisine of the Mediterranean region. The convex shape of lentils resulted in thier Latin name being coined for glass possessing the same shape.

Because of the way in which lenses refract light that strikes them, they are used to concentrate or disperse light. Light entering a lens can be altered in many different ways according, for example, to the composition, size, thickness, curvature and combination of the lens used. Many different kinds of lenses are manufactured for use in such devices as cameras, telescopes, microscopes and eyeglasses. Copying machines, image scanners, optical fiber transponders and cutting-edge semiconductor production equipment are other more recent devices in which the ability of lenses to diffuse or condense light is put to use.