Lesson Notes By Weeks and Term v4 - SHS 3
ATOMIC PHYSICS
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
ATOMIC PHYSICS
Download the Lessonotes Mobile Ghana app for faster lesson access on Android and iPhone.
Subject: Physics
Class: SHS 3
Term: 2nd Term
Week: 17
Grade code: 3.3.4.LI.2
Strand code: 4
Sub-strand code: 1
Content standard code: 3.3.4.CS.3
Indicator code: 3.3.4.LI.2
Theme: ATOMIC AND NUCLEAR PHYSICS
Subtheme: ATOMIC PHYSICS
This page supports the lesson note with a companion video and a short classroom-ready summary.
For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.
In our daily lives in Ghana, from Accra to Bolgatanga, we are surrounded by rechargeable devices: our mobile phones, laptops, 'chargeable' lamps and fans that save us during 'dumsor', and even the batteries in cars and solar power systems. But have you ever wondered about the science that allows us to plug a device into a wall socket and safely store electrical energy in a battery? This lesson bridges the gap between the abstract world of atoms and the practical technology of a battery charger. We will discover how the behaviour of electrons in different materials, a core concept of Atomic Physics, is harnessed to create the essential components that make a charger work.
This section breaks down the fundamental physics required to understand and design a battery charger. 2.1. Energy Band Theory in Solids
In an isolated atom, electrons exist in discrete energy levels. However, when atoms come together to form a solid, these energy levels interact and broaden into continuous bands of allowed energy, separated by forbidden energy gaps. Valence Band: The outermost energy band that is completely filled with electrons at absolute zero temperature. Electrons in this band are involved in bonding and are not free to move. Conduction Band: The next allowed energy band above the valence band. It is normally empty. Electrons in this band are free to move and conduct electricity. Forbidden Energy Gap (E_g): The energy difference between the top of the valence band and the bottom of the conduction band. No electrons can exist in this gap. The size of this gap determines the material's electrical properties. Conductors (e.g., Copper, Silver): The valence and conduction bands overlap (E_g ≈ 0 eV). A large number of free electrons are available to conduct electricity with even a small applied voltage. Insulators (e.g., Wood, Rubber, Glass): The forbidden energy gap is very large (E_g > 3 eV). It requires a huge amount of energy to move an electron from the valence to the conduction band. Therefore, they do not conduct electricity under normal conditions. Semiconductors (e.g., Silicon (Si), Germanium (Ge)): The forbidden energy gap is small (E_g ≈ 1 eV). At room temperature, some electrons gain enough thermal energy to jump into the conduction band, allowing for a small amount of conductivity. This conductivity can be precisely controlled, which is what makes them so useful. 2.2. Doping and Types of Semiconductors
The conductivity of a pure (intrinsic) semiconductor is too low for most applications. We can dramatically increase it by a process called doping – deliberately adding a small amount of impurity atoms. N-type Semiconductor: Created by doping a pure semiconductor (like Silicon, Group IV) with a pentavalent impurity (Group V, e.g., Phosphorus). The impurity atom provides an extra, "free" electron, which becomes the majority charge carrier. 'N' stands for negative. P-type Semiconductor: Created by doping with a trivalent impurity (Group III, e.g., Boron). The impurity atom creates a vacancy or a "hole" where an electron should be. This hole acts as a positive charge carrier and is the majority charge carrier. 'P' stands for positive. 2.3. The P-N Junction Diode: The Heart of the Charger
A P-N junction is formed by joining a piece of P-type semiconductor to a piece of N-type semiconductor. This simple device is the foundation of modern electronics. Formation: When joined, free electrons from the N-side diffuse across the junction to fill holes on the P-side. This leaves behind positive ions on the N-side and creates negative ions on the P-side. Depletion Region: This process creates a thin region at the junction that is depleted of free charge carriers. An electric field, called the potential barrier, is established across this region, preventing further diffusion.