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# ("Photoelectric effect in magnetic field") A small metallic ball is suspended at the center of a cylindrical glass vessel of radius R.

("Photoelectric effect in magnetic field") A small metallic ball is suspended at the center of a cylindrical glass vessel of radius R. A monochromatic light of frequency f illuminates the surface of the ball, and the photo-electrons are being emitted. The inside of the vessel is in high vacuum, and the inner wall of the side of the cylinder is coated with phosphorus, so that it glows when the photo-electrons are able to reach it.

(a) Under these conditions, what is the maximal kinetic energy of the photo-electrons? The work function of the metal is ΦW .

(b) The whole system is placed in a big electromagnet capable of producing a homogeneous magnetic field throughout the glass vessel. The field is collinear with the 1 axis of the cylinder. What is the minimal magnetic field, Bmin, necessary to stop the side of the glass vessel from glowing - that is, to prevent the photo-electrons from reaching its surface? What is the dependence of Bmin on f?

(c) Can we use this apparatus to study the photoelectric effect? Imagine that we can't measure B directly, but only measure the current I that goes through the electromagnet. (That would be a more realistic scenario.) Will we still be able to prove that the energy of the photon only depends on the frequency and not on the intensity of the light? (Please explain why, or why not.)

#### Top Answer

Answers: (a) (1/2).m.v max 2 = hf - W 0 (b) (i) B = (2/Rq)... View the full answer

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