# The gold leaf electroscope and the photoelectric effect

• zoya76
In summary, when you charge an electroscope with a negatively charged rod, electrons are repelled to the bottom of the electroscope and the gold leaf rises. When you shine light above the fundamental frequency on the top plate of the electroscope, electrons are liberated from the plate and the leaf falls. These electrons are liberated into the surroundings and form an electron cloud which expands under mutual repulsion.
zoya76
When you charge an electroscope with a negatively charged rod, electrons are repelled to the bottom of the electroscope and the gold leaf rises. Then when you shine light above the fundamental frequency on the top plate of the electroscope, electrons are liberated from the plate and the leaf falls.

What I don't understand
Where are these electrons liberated too? Where do they go? And are they dragged up from the gold leaf before being liberated somewhere? If they are liberated from the plate itself (too somewhere) then surely the plate will get even more positively charged and therefore the leaf would stay elevated. Am I missing something?

Hello zoya76,

Welcome to Physics Forums!

Maybe the problem statement is implying that the electrocsope is charged by touching the top plate with the negatively charged rod. That would give a net negative charge to the whole kit and kaboodle (i.e. the top plate and the gold leaf). This would cause the gold leaf to rise due to its net negative charge, and the top plate would maintain a negative charge too (that is, until you neutralize the whole thing by blasting some electrons off the top plate by shining a high-frequency light on it).

Last edited:
zoya76 said:
When you charge an electroscope with a negatively charged rod, electrons are repelled to the bottom of the electroscope and the gold leaf rises. Then when you shine light above the fundamental frequency on the top plate of the electroscope, electrons are liberated from the plate and the leaf falls.

What I don't understand
Where are these electrons liberated too? Where do they go? And are they dragged up from the gold leaf before being liberated somewhere? If they are liberated from the plate itself (too somewhere) then surely the plate will get even more positively charged and therefore the leaf would stay elevated. Am I missing something?

I think that initially the electrons are liberated into the surroundings and form an electron cloud which expands under mutual repulsion as more electrons are added.I have a vague memory of something called the Richardson Dushman equation which quantifies the cloud formed by thermionic emission.Try googling to see if this equation or some sort of variation of it can be applied to photoelectric emission and answer your question in greater depth.

Thanks guys. It makes sense now. I think I'll have to use this forum more frequently!

## 1. What is a gold leaf electroscope?

A gold leaf electroscope is a scientific instrument used to detect and measure the presence of electric charge. It consists of a metal rod with two thin gold leaves attached to the bottom. When an electric charge is applied to the rod, the leaves will either repel or attract each other, indicating the presence and type of charge.

## 2. How does a gold leaf electroscope work?

The gold leaf electroscope works based on the principle of electrostatic repulsion. When a charged object is brought near the metal rod, it will induce a charge in the rod, causing the leaves to repel each other. This repulsion is used to detect the presence of an electric charge.

## 3. What is the photoelectric effect?

The photoelectric effect is the phenomenon where electrons are ejected from a material when it is exposed to light. This effect was first observed by Heinrich Hertz in 1887 and has since been explained by Albert Einstein's theory of quantum physics.

## 4. How does the photoelectric effect relate to the gold leaf electroscope?

The photoelectric effect is used in the gold leaf electroscope to detect the presence of electromagnetic radiation, such as visible light. When light is shone on the metal rod, it can cause the release of electrons, which can then be detected by the movement of the gold leaves.

## 5. What are the practical applications of the gold leaf electroscope and the photoelectric effect?

The gold leaf electroscope has many applications in science and engineering, such as detecting the presence of static electricity, measuring the intensity of radiation, and testing for the presence of radioactive materials. The photoelectric effect has also been used in various technologies, including solar cells, photomultiplier tubes, and digital cameras.

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