Question

When potassium metal is exposed to violet light: (a) There is no effect (b) Ejection of electron takes place (c) The absorption of electrons takes place (d) Ejection of some potassium atoms occurs

Short answer

(b) Ejection of electron takes place.

Step-by-step solution

Understanding the Photoelectric Effect

The photoelectric effect refers to the ejection of electrons from the surface of a metal when it is exposed to light of a certain minimum frequency. This occurs because the energy of the photons in the light is absorbed by electrons in the metal, providing them with enough energy to overcome the attractive forces holding them within the metal.

Determine the Energy of Violet Light

Violet light is part of the visible spectrum with a high frequency and energy. Photons of violet light carry more energy compared to other colors within the visible light spectrum, which makes them likely candidates for causing the photoelectric effect when interacting with metals like potassium.

Applying the Photoelectric Effect to Potassium

Potassium is a metal with a relatively low work function, meaning it requires less energy to release its electrons compared to many other metals. When potassium is exposed to high-energy photons, such as those present in violet light, the energetic photons can transfer enough energy to the electrons in the metal to cause them to be ejected.

Choose the Correct Effect

Given that violet light provides enough energy to cause the ejection of electrons from metals with low work functions, exposure of potassium to violet light will most likely result in electron ejection. This aligns with the principles of the photoelectric effect.

Key concepts

Violet Light and Its Properties

Violet light is a fascinating part of the visible spectrum, known for its high frequency and energy. It sits at the edge of the visible light spectrum, just before ultraviolet light, which makes it one of the most energetic forms of visible light. Due to its high frequency, violet light carries more energy in its photons compared to other colors like red or yellow.
This energy is crucial in many scientific phenomena, including the photoelectric effect. Let's break down some key points:

• Violet light has shorter wavelengths and higher frequencies than other visible light.
• It typically has wavelengths between 380 to 450 nanometers.
• Due to its high energy, it plays a significant role in processes requiring substantial energy input, such as electron ejection.

When violet light interacts with certain materials, it can impart enough energy to cause electrons to escape, especially from metals with lower work functions, like potassium.

Characteristics of Potassium Metal

Potassium metal is known for its unique properties, which make it particularly susceptible to the photoelectric effect. Among the alkali metals, potassium stands out due to its low work function, meaning it requires less energy for electrons to be ejected from its surface.
This characteristic makes it an excellent candidate for observing the effects when exposed to high-energy light, such as violet light. Key characteristics of potassium include:

• Its position as an alkali metal in the periodic table, resulting in a single electron in its outer shell.
• A low work function, allowing easier electron escape when exposed to energetic light.
• High reactivity, often requiring careful handling outside an inert environment.

The combination of low work function and high reactivity makes potassium ideal for photoelectric experiments, especially under light with high photon energy, like violet.

Electron Ejection and the Photoelectric Effect

Electron ejection is the fundamental concept behind the photoelectric effect. This physical phenomenon occurs when light of sufficient energy strikes the surface of a metal, such as potassium, causing electrons to be ejected.
The process is governed by several crucial principles. Let's explore how it works:

• When light hits a metal surface, photons transfer energy to electrons.
• If this energy exceeds the metal's work function, electrons overcome the attractive forces binding them.
• Ejected electrons, also known as photoelectrons, are observed as a current or as individual particles.

In the case of potassium exposed to violet light, the high-energy photons of violet light efficiently transfer energy to potassium’s electrons, overcoming the low work function, and resulting in electron ejection.
This emphasizes the importance of both the light's energy and the metal's properties in the photoelectric effect.