Sciences Dissertations | Photoelectric Effect Electrons

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Assessment Task Topic: The Photoelectric Effect

1. Introduction

The photoelectric effect is the name given to the phenomenon whereby electrons are emitted from a metal when exposed to electromagnetic radiation of the appropriate frequency. It was first discovered by Heinrich Hertz in 1887, but remained a conundrum to many scientists who sought to explain it, as it clearly contradicted the accepted principles of classical physics such as James Clerk Maxwell’s Theory of Electromagnetic Waves. This phenomenon, unable to be explained by the wave model of light, was finally explained by Albert Einstein in 1905 with the inception of his Quantum Theory, a concept that would completely revolutionise scientific thought. The photoelectric effect has played and continues to play an important role in mankind’s scientific development.

2. Discovery of the Photoelectric Effect: Hertz

The original observation of the photoelectric effect can be traced back to the German scientist Heinrich Hertz. In 1887, in an attempt to generate and detect electromagnetic radiation, Hertz created a rapidly-oscillating electric field with a high voltage induction coil to cause a spark discharge between two spherical brass electrodes. He observed that when a small length of copper wire with brass spheres attached on either end was bent into a loop, leaving a small gap between the spheres, and held near the sparking induction coil, a spark would jump across the gap at the same time when the brass electrodes in the induction loop sparked. This induced spark occurred despite the copper loop not being connected to any electrical current source. Thus Hertz came to the conclusion that the copper loop was a detector of the electromagnetic waves propagated by the transmitting loop.

This successful experiment was followed up by a series of others, through which Hertz demonstrated that these electromagnetic waves could be reflected from a metal mirror, and refracted as they passed through a prism made from pitch, thus proving that these waves behaved similarly to light waves. He also proved these waves were polarised.

Through the course of his investigations, he discovered a mysterious phenomenon: “I occasionally enclosed the spark B[the detector spark]in a dark case so as to more easily make the observations; and in so doing I observed that the maximum spark-length became decidedly smaller in the case than it was before. On removing in succession the various parts of the case, it was seen that the only portion of it which exercised this prejudicial effect was that which screened the spark B from the spark A[the transmitter spark]. The partition on that side exhibited this effect, not only when it was in the immediate neighbourhood of the spark B, but also when it was interposed at greater distances from B between A and B. A phenomenon so remarkable called for closer investigation.”

Upon shielding the detecting loop with glass, the intensity of the spark produced was reduced. However, when a quartz shield (a substance that allows UV rays to pass) was applied,

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