Physics

In solar cells, electron emission converts the light energy into electrical energy through the photoelectric effect. Solar cells work due to photoelectric effect, in which photons from sunlight strike solar cell surface. When a photon that has sufficient energy hits the surface, it transfers its energy to an electron in the material of solar cell surface. This causes the electron emission from its bound state. Solar cells can use photoelectric effect to generate electron-hole pairs that are separated and collected for producing electrical current. This provides a renewable source of power.

Electron emission is used for generating a beam of electrons in an electron microscope. An electron microscope requires a source of electrons for creating a beam of electrons. This source can be mostly a gun that uses electron emission for producing free electrons. Once the electrons are emitted, they are accelerated by anode and then, they are focused as a fine beam through a series of electromagnetic lenses. The beam is then directed onto the specimen that is being examined.

The work function in electron emission is the minimum amount of energy needed for removing an electron from the surface of a material. This function is denoted as? , and it is measured in electron volts. An electron requires at least the work function as energy to escape the surface of a solid material into the vacuum. This represents the difference between energy of an electron at rest in vacuum and fermi level of the material. Work function varies from material to material.

A camera lens focuses the light onto a light-sensitive surface like film or a digital sensor for capturing an image. The camera lens gathers as much light as possible for forming a clear and bright image. This lens focuses the collected light on a specific point like camera's film or its digital sensor. The focus is achieved due to the curvature of lens and the arrangement of its optical elements. This lens refracts light rays so that they converge at focal plane where film/sensor is located.

A telescope functions on the working principle of gathering light form distant source and then, forming image which can be magnified for observation. Based on their design, there are two types of telescopes including refracting telescopes and reflecting telescopes. A refracting telescope has a front lens called as objective lens. This front lens is a convex lens that collects light from distant objects and then bend it to the focal point. In a reflecting telescope, a concave mirror is the primary mirror that collects light and then, reflects it to a focal point.

As we all know that like charges repel each other. This means that there must be a repulsive electromagnetic force between positively charged protons. However, the nuclear force is said to be 100 times stronger than electromagnetic force which makes it strong enough to hold protons together within a nucleus. This nuclear force is much stronger than coulomb force at short ranges.

Cross product will represent a vector perpendicular to both the vector.

Dir. Of Motion of P : $=\left(\widehat{i}+\widehat{j}\right)*\left(\widehat{j}*\widehat{k}\right)$ $\stackrel{}{}\stackrel{}{}\stackrel{}{}\stackrel{}{}$

= $\widehat{k}-\widehat{j}+\widehat{i}$ $\stackrel{}{}\stackrel{}{}$

Dir. Of Motion of Q = $\left(\widehat{i}+\widehat{j}\right)*\left(-\widehat{i}+\widehat{j}\right)$ $\stackrel{}{}\stackrel{}{}\stackrel{}{}\stackrel{}{}$

$=2\widehat{k}$

$cos\theta =\frac{\overrightarrow{a}.\overrightarrow{b}}{ab}=\frac{2}{2\sqrt[]{3}}=\frac{1}{\sqrt[]{3}}\Rightarrow \theta =co{s}^{-1}\left(\frac{1}{\sqrt[]{3}}\right)$