Lesson Notes By Weeks and Term v4 - SHS 3
ATOMIC PHYSICS
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ATOMIC PHYSICS
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Subject: Physics
Class: SHS 3
Term: 2nd Term
Week: 18
Grade code: 3.4.1.LI.3
Strand code: 4
Sub-strand code: 1
Content standard code: 3.4.1.CS.1
Indicator code: 3.4.1.LI.3
Theme: ATOMIC AND NUCLEAR PHYSICS
Subtheme: ATOMIC PHYSICS
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This lesson introduces the fundamental properties of X-rays, a crucial type of electromagnetic radiation discovered within the study of atomic physics. We will explore how these invisible rays are produced and learn how to calculate their key characteristics: energy, frequency, and wavelength. Understanding X-rays is vital, not just for passing WASSCE, but also for appreciating modern technology that we see in our daily lives, from medical check-ups at Korle-Bu Teaching Hospital to security checks at Kotoka International Airport. This lesson connects the abstract world of atoms and electrons to the powerful, practical applications that keep us safe and healthy.
A. What are X-rays?
X-rays are a form of high-energy electromagnetic radiation. Just like visible light, radio waves, and microwaves, they are part of the electromagnetic spectrum. However, they have much shorter wavelengths (typically 0.01 to 10 nanometres) and much higher frequencies, which gives them a large amount of energy. This high energy allows them to pass through many materials that are opaque to visible light, such as skin and muscle, but they are stopped by denser materials like bone and metal. B. How X-rays are Produced (The Atomic Physics Connection)
X-rays are produced in a device called an X-ray tube. The process is a direct application of atomic physics: A filament (cathode) is heated, causing it to release electrons through thermionic emission. A very high potential difference (voltage), typically in kilovolts (kV), is applied between the cathode and a metal target (anode), usually made of a dense material like Tungsten. This high voltage accelerates the electrons to a very high speed, giving them a large amount of kinetic energy (KE). These high-speed electrons smash into the metal target. When the electrons are suddenly stopped or slowed down ("braked") by the atoms in the target, their kinetic energy is converted into other forms, primarily heat and electromagnetic radiation. The electromagnetic radiation produced is an X-ray photon.
The maximum energy of the X-ray photon produced is equal to the maximum kinetic energy of the electron that was stopped. This is the key principle for our calculations.