Problem 2 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The metal mainly used in devising photoelectric cells is : (a) \(\mathrm{Na}\) (b) Li (c) \(\mathrm{Rb}\) (d) \(\mathrm{Cs}\)

Step-by-Step Solution

Answer

Cesium (Cs) is the metal mainly used in photoelectric cells.

Step 1: Identify the Requirement

In the given question, we need to identify which metal is primarily used in the creation of photoelectric cells. Photoelectric cells are devices that convert light into electrical energy via the photoelectric effect.

Step 2: Understanding the Photoelectric Effect

The photoelectric effect occurs when light hits a metal surface and causes it to emit electrons. It efficiently occurs in metals with lower work functions, meaning lower energy needed to eject electrons.

Step 3: Comparing Metals for Photoelectric Cells

The metals listed are: Sodium (Na), Lithium (Li), Rubidium (Rb), and Cesium (Cs). Among these, Cesium (Cs) is known for having a relatively low work function compared to the others. This property makes it ideal for use in photoelectric cells.

Step 4: Conclusion

Considering the properties of the metals, Cesium (Cs) is commonly used in photoelectric cells due to its low work function.

Key Concepts

Metal with Low Work Function

In the realm of photoelectric cells, a crucial concept is the term "work function." Simply put, the work function is the minimum energy required to remove an electron from the surface of a metal. Metals with a low work function are particularly interesting for photoelectric applications because they require less energy to liberate electrons, making them more efficient in converting light to electricity.

• Cesium, for example, is a metal with a notably low work function of approximately 2.1 eV, making it an excellent choice for photoelectric cells.
• A material that needs higher energy (or higher work function) will not eject electrons as easily when light is shone upon it. Therefore, it's less efficient.

Choosing metals with low work function enables the creation of devices that can effectively harness solar energy by easily releasing electrons. These metals simplify the process of converting light into electrical energy, making them both vital and efficient in the field of photoelectric technology.

Photoelectric Effect

The photoelectric effect is a fundamental concept that explains how light can induce electrical energy production. It was first explained by Albert Einstein, earning him a Nobel Prize. Here’s how it works: when light strikes a material with a low work function, it can cause electrons to be ejected from that material's surface.

• When photons, which are particles of light, hit a metal surface, their energy can be transferred to electrons in the metal.
• If the photon's energy is greater than the work function of the material, electrons will be emitted.
• This effect is central to creating photoelectric cells, as it directly translates light energy into electrical energy, thus facilitating a renewable energy source.

Photons of light must have enough energy, known as their "frequency," to surpass the work function energy barrier for electrons to be released. In photoelectric cells, this process is deliberately harnessed to create electricity efficiently.

Electron Emission

Electron emission refers to the release of electrons from a substance, commonly achieved in metals by using the photoelectric effect. When discussing photoelectric cells, electron emission is crucial because it converts light energy directly into a flow of electrical current.

• The ejected electrons, known as photoelectrons, can be collected to create a usable electrical current.
• Once emitted, electrons can travel through a circuit, providing power to various devices or systems.
• Lower energy input for electron emission is desired in photoelectric cells to optimize efficiency.

Essentially, electron emission is the bridge between light and electricity, allowing for the practical application of light-induced energy. The process is maximized when metals with a low work function are used, as they enable an easier and more efficient conversion of light energy into electrical energy.