Consider a device we will call a \"spin-1/2 filter.\" This simply consists of St

Question

Consider a device we will call a "spin-1/2 filter." This simply consists of Stem-Gerlach apparatus where one of the two outgoing beams of electrons is blocked, so that only the other beam emerges. Suppose we employ two such filters in succession. Discuss what emerges from the second filter compared to what goes in the first filter for each of the following cases. The filters are arranged so that their north and south magnets are aligned in the same manner. The filters are arranged so that their north and south magnets are rotated through 180 degree with each other. The filters are arranged so that their north and south magnets are at right angles to each other. Discuss how this compares with the filtering phenomenon we see with light passing through polaroids.

Explanation / Answer

a) If both the poles are aligned in the same manner then they measure electrons with same spin. So all the electrons passing through first device will also pass through second device.

b) If both the poles are rotated through 180 deg then one measure electrons with spin 1/2 and second device measure electrons with spin -1/2. So no electron pass through second device.

c) If both are aligned through right angles to each other then one measure spin-1/2 in x-direction and second device measures the spin-1/2 in y-direction. So half of the electrons coming from first device will pass through second device.

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