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What is the principle used in the working of 3D glasses?

Sreeda asked:

What is the principle used in the working of 3D glasses?


3D glasses are actually polaroids. They are not creating the 3D effects. The 3 D movies are filmatographed with two cameras help at two different angles just like we see with TWO eyes.

The two films are projected on the screen with polarized light with their plane of polarization in perpendicular to each other. If we look at the screen without ant 3D glass we will see blurred images only as the two pictures are overlapping each other and both the image are seen together by both the eyes.

3D glasses use Polaroid with the plane of polarization in mutually perpendicular directions. So, when we wear the Polaroid glasses and look at the screen, only one of the image will be seen by one of the eyes and the second eye sees the other image. This creates the 3D sensation, we are seeing the image filmed with the left camera with the left aye and that with the right camera with right eye.

MAGNETISM : Why repulsion is told to be the test for magnetism?

Sreeda sked:

“Can a magnet lose its magnetic properties?How?
Why ‘repulsion’ and not ‘attraction’  is suggested to be a good test of finding whether a substance is a magnet or not?”


A magnet can lose its magnetism.

A magnetic substance is made a magnet by making the molecules which are individually possessing magnetic properties align in a particular direction. In the unmagnetized state they are arranged randomly and hence do not have magnetic behaviour.

If a magnet is heated, beaten, mishandled etc, it will lose its magnetism.

Why repulsion is the sure test for magnetism?

A magnet can attract the opposite pole of other magnet as well as the magnetic substance (iron cobalt nickel). SO, if A magnet attracts another object, we cannot say that the other object is a magnet. But if the magnet repels the object, then we can surely say that the other object is a magnet. Because “Like poles of a magnet repel each other”

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