Question

lenard's observation explaination..?​

Answer 1

Answer:

Hertz's Observation:

In 1887 by Heinrich Hertz observed that when light falls on a metal surface, some electrons near the surface absorb enough energy from the incident radiation to overcome the attraction of the positive ions in the material of the surface.

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Answer 2

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• It was in 1887 when Heinrich Hertz was conducting experiments to prove Maxwell’s electromagnetic theory of light, that he noticed a strange phenomenon. Hertz used a spark gap (two sharp electrodes placed at a small distance so that electric sparks can be generated) to detect the presence of electromagnetic waves. To get a closer look, he placed it in a dark box and found that the spark length was reduced. When he used a glass box, the spark length increased and when he replaced it with a quartz box, the spark length increased further. This was the first observation of the photoelectric effect.

Observations

• The photoelectric current (same as the rate of emission of electrons) is directly proportional to the intensity of light falling on the electrode. Note from the figure below that with increasing intensity the current is increasing. Also, observe that as the voltage has decreased the current also decreases. But to obtain zero current, the voltage has to be reversed to a certain V­0 known as the stopping potential. The voltage must be reversed to such an extent that the electrons cannot reach the anode. This is the maximum kinetic energy an emitted electron can achieve,

Maximum Kinetic energy,KE = eV°

(e is the charge of the electron)

• The Maximum kinetic energy increases with increase in the frequency of light. With a higher frequency of light (ν), the stopping potential becomes more negative which implies that the kinetic energy of electrons also increases.

• All frequencies of light, however, cannot cause a photoelectric current to develop. Only light above a certain frequency (ν0) can produce a photoelectric current. This frequency is known as the threshold frequency. This varies with the electrode material. Also, the maximum kinetic energy of the electrons increases linearly with increasing light frequency. If we extend the graph below the x-axis, the intercept on the Kinetic energy axis represents the minimum energy required for emission of the electron; this is known as the work function of the material.

• Lastly, the electron emission occurs instantly without any time lag.