Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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.

Performance objectives

• Define energy, frequency, and wavelength.
• Calculate the energy of a photon using E = hf.
• Determine the frequency of X-rays.
• Calculate the wavelength of X-rays using λ = c/f.

Lesson summary

This lesson delves into the fascinating world of X-rays, a high-energy form of electromagnetic radiation. We will explore how these invisible rays are produced and learn the fundamental relationships that govern their energy, frequency, and wavelength. Understanding X-rays is crucial not only for physics but also for our daily lives in Ghana. From a doctor at the Korle Bu Teaching Hospital diagnosing a bone fracture to a security officer at Kotoka International Airport scanning luggage, the principles we will learn today are applied every day to keep us safe and healthy. This lesson connects concepts of electricity (voltage), energy, and wave mechanics into a single, powerful application.

Lesson notes

2.1 How are X-rays Produced?

X-rays are produced when fast-moving electrons are suddenly stopped or decelerated. This process typically happens inside a device called an X-ray tube.

Here is a step-by-step breakdown of what happens inside an X-ray tube: Thermionic Emission: A filament (cathode) is heated by a low voltage supply. This heat gives the electrons in the filament enough energy to escape from the metal surface. This process is called thermionic emission. Acceleration: A very high potential difference (voltage), often thousands of volts (kilovolts, kV), is applied between the heated filament (cathode, negative) and a metal target (anode, positive). High-Speed Collision: The emitted electrons are strongly attracted to the positive anode and accelerate across the vacuum tube, gaining a large amount of kinetic energy. Deceleration and Energy Conversion: The high-speed electrons violently collide with the dense metal target (often made of tungsten). Upon impact, they are forced to stop or slow down very abruptly. According to the principle of conservation of energy, the kinetic energy lost by the electrons must be converted into other forms. A small amount becomes heat (about 99%), and a tiny but significant fraction (about 1%) is converted into high-energy electromagnetic radiation – X-ray photons. 2.2 The Physics of X-ray Production: Key Formulas

The entire calculation process hinges on one fundamental principle of energy conservation:

Evaluation guide

• Calculate the energy, frequency and wavelength of x -rays.
• Experiential learning: Let learners employ their knowledge in calculating the energy of a
• photon to determine the frequency of x -rays produced.
• conceptual