Why we need to use immersion oil in the 100x objective?

Question

why we need to use immersion oil in the 100x objective

Answer 1

Immersionoil touches the objective lense and it forms another lens. The refractive index of the oil is equal to that of the glass from which the objective lens is made up of. So it just goes well with the objective lens. It further magnifies the object.

Answer 2

It's all about the refraction of light.  If you look at something under the 100x objective, you'll see the image is blurry without any sort of sharpness to it.  The reason is because the light that is reflected off the thing on the slide doesn't enter the objective, but rather bends too little and all of it enters the lens.  The immersion oil decreases the amount of refraction, thus causing the light to enter the lens less and revealing under the microscope darker areas where the thing on the slide actually is.

It may be the other way round, with light entering the lens too little, but I think it's this way.

The person below me is somewhat correct, but the fact is that if light never left the fluid, all of it would enter the lens, and in doing so cause you to be unable to see whatever is on the slide.  The light does exit the fluid, and the difference the fluid causes is in the angle of the light, thus changing the amount of light that enters the lens.

Answer 3

I read the previous answer and i didnt really understand what he was talking about the light and dark areas. I think what he is talking about is the diaphragm, which you can adjust the amount of light coming in (effects the depth of field and contrast of an image). Like the aperture on a camera.

So the answer to your question is :

But generally when you magnify something so great, the specimen you want to look at is in some water. So the light must go from the liquid the specimen is in, to plain air, then into the lens.  Light bends when it leaves water, and since the magnification is so great the bending and distortion of the light ruins the image making it too blurry to see.

SO what the oil does is you put it on top of the coverslip so the lens is touching the oil. Therefor the light never has to go into the air, it always stays in a liquid and the bending (distortion) is reduced to almost no distortion.

Answer 4

Passing light through media with different refractive indeces reduces the quality if the image.  The refractive index of oil is similar to that of the glass in the lens thus reducing the amount of image degradation.