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Hertz Lenard Observations

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Last updated date: 09th Apr 2024
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Hertz and Lenard’s Observations

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


A year later we can say that Wilhelm Hallwachs generally confirmed these results and showed that light which was the UV light on a Zinc plate that is connected to a battery generated a current that is because of electron emission.  J.J. Thompson in 1898 found that the amount of current varies with the frequency and intensity of the radiation that is used.


Later in 1908, Lenard Observed that the kinetic energy of electrons which are emitted increased with the frequency of radiation that is used. This could not be explained as the theory of Maxwell’s electromagnetic which Hertz proved correct, predicted that the energy which is kinetic should be only dependent on light intensity and not on the frequency.


The resolution which we have discussed would only come a few years later that too from famous scientist  Einstein when he would provide an explanation to the Photoelectric Effect.


Hertz Lenard Observations


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To test the hypothesis of Maxwell's Hertz that is used, an oscillator which is made of polished brass knobs that each one is connected to an induction coil and separated by a tiny gap that is over which sparks could leap. To confirm this whole thing that we have discussed, Hertz made a simple receiver of looped wire. Its ends are separated by a tiny gap as we will notice this. The receiver present was placed several yards from the oscillator. Hertz reasoned that if Maxwell's had the predictions which were said to be correct, electromagnetic waves would be transmitted during each series of sparks that would induce a current which is in the loop that would send the sparks that too across the gap. This generally occurred when Hertz turned on the oscillator and produced the first reception and the transmission of electromagnetic waves. Hertz also noted that a conductor which is electrical reflects the waves and that they can be focused that too by a reflector that is concave. He found that the nonconductors generally allow most of the waves to pass through. The phenomenon of photoelectric emission was discovered in the year 1887 by Heinrich Hertz during the electromagnetic wave experiments. He generally observed that when the light falls on a surface of a metal, some of the electrons that are near the surface absorb energy which is enough from the incident radiation to overcome the attraction which is of the positive ions which are in the material of the surface.


Hertz and Lenard's Observations of the Photoelectric Effect

This observation that we have seen that is related to the effect which is photoelectric and how this effect is proven by two scientists is one of the experiments that was conducted in 1887 by Heinrich Hertz to prove the theory of electromagnetic light when he observed strange phenomena as he placed two electrodes at a very small distance. So we can say here that an electric spark can be generated and he used a spark gap to apply this experiment so that he can easily observe the presence of waves which are electromagnetic. The same which we can say is the case with Lenard as he observed the kinetic energy of electrons which are emitted and then increased with the radiation that is used. Both of their experiments show the different types of samples or we can say that the experiment to prove the same thing but they all were given green signals and only when this was confirmed and proven by Einstein.


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Every metal that we have learnt consists of certain minimum frequency which is of incident radiation below which no photoelectrons are emitted or are not able to emit this type of frequency is known as the threshold frequency The increasing frequency of the beam which is incident keep the number of photons that are fixed and this would keep the proportionate increase in energy and also this increases the kinetic energy to its maximum and leads to stopping the voltage which is increased. It is also generally mentioned that if the intensity which is of the radiation that is incident is said to be increased when there will be no effect on the kinetic energy of photoelectrons as kinetic energy depends upon the frequency that is of light and thus, the level of energy provided by each photon. On the other hand, we can say that stopping the voltage does not depend on the intensity of the light but we can say that it is generally provided with the light frequency that is to be fixed at a point.


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In a subject like physics, kinetic energy is the energy that is possessed by an object which is moving or by its motion. In other words, we can say that it can be defined as work which is required by a body which is to accelerate from its actual position to the position it wants to reach and the body which keeps this kinetic energy until and unless it changes its speed. Same goes with the case of accelerating the body which is from moving at a speed that is to divert itself towards the rating part. It is said that the energy that generally occurs in many forms which include energy which is chemical or we can also say the thermal energy and the electromagnetic energy that includes nuclear energy and rest energy and many more can be added to this category. Thus, kinetic energy can be seen in a moving object and also in the resting one.

FAQs on Hertz Lenard Observations

1. What is Hertz Observation on Photoelectric Effect?

The Photoelectric Effect was discovered in 1887 by the German physicist Heinrich Rudolf Hertz. In connection with all that, we have discussed the work on radio waves that Hertz Observed that when the ultraviolet light shines on two metal electrodes with a voltage that is applied across them, the light changes the voltage at which sparking takes place generally.

2. Explain what Hertz and Lenard's observation is.

Hertz used a gap of spark, i.e. the two sharp electrodes that were placed at a distance which is small so that the electric sparks that can be generated which is to detect the presence of wave which is electromagnetic. To get an even closer look , he placed it in a dark box and then he found that the spark length was reduced.

3. What is Hertz’s Observation?

The Hertz's Observation: Heinrich Hertz in 1887 observed that when light falls on a metal surface some electrons that are near the surface absorb enough energy from the incident radiation to overcome the attraction of the positive ions in the material of the surface.

4. What is the Hertz effect?

The effect of the radiation which is ultraviolet in lowering the sparking voltage that is across a spark gap: an example we can take is the Photoelectric Effect.

5. What is the Photoelectric Effect?

Photoelectric Effect can be described as the phenomenon where the electrically charged particles are lost from a material when the particles start absorbing electromagnetic radiation. This phenomenon is the removal of electrons from a plate made of a metal compound when light falls there. The light that falls on the plate may be infrared, ultraviolet light, gamma, or X-rays, and the material at which it falls may be of any form i.e. solid, gas or liquid. The released particles are ions or electrons. This phenomenon was important for modern physics development as there was much confusion related to the nature of light which was finally explained by Einstein in the year 1905.  

6. What are the applications of the Photoelectric Effect?

There are many applications that are related to the Photoelectric Effect which are directly dependent on the intensity of light and also the frequency. One of the devices we see is the photoelectric cell which was originally the phototube. It is a vacuum tube that has a cathode that is made of metal. It functions to emit electrons. The current that is released is held by the anode. A photoelectric cell can detect light and also measure the intensity of light. It can also control the illumination of other devices and turn light into electrical energy. These work on low voltages and they are important for industrial usage. They are also used in solar cells and telecommunication networks and have many applications.

7. What are photoconductive cells?

Photoconductive cells are cells that are composed of semiconductors and have band-gaps. These correspond to the energies of the photons to be sensed. We can observe such cells in the exposure meters and automatic switches of the street lamps which operate in the visible spectrum. They are made of cadmium sulfide. The infrared detectors like the night-vision sensors are such examples. These are made of mercury cadmium telluride or sulfur cadmium telluride.

8. What was Lenard’s experiment?

Lenard and Hallwachs experimented on the phenomenon of photoelectric emission between the years 1886 and 1902. Their observations are as follows:

  • When light falls on the metal plate, the electrons are removed from it.

  • They also observed that when light falls on the plate then electrons are not emitted when the frequency is lower than the frequency of the light that falls on the plate. This frequency was named the threshold energy.

  • They also observed that different metals were of different frequencies of threshold energy.

9. Give one observation made by Hertz-Lenard.

Lenard and Hallwachs experimented on the phenomenon of photoelectric emission between the years 1886-1902. One of the observations they made is that the photoelectric current was directly dependent on the intensity of light that fell on the electric plate. When the intensity of light is increased then there is an increase in current as well. When the voltage is decreased then this results in a decrease of current as well. To obtain no amount of current, the voltage was reversed to an extent where the electrons couldn’t reach the anode.