Lesson Notes By Weeks and Term v4 - SHS 2

Lesson Video

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Performance objectives

• Explain the force on a moving charged particle in an electric field.
• Describe factors affecting a particle's motion in a magnetic field.
• Understand the Lorentz force in crossed electric and magnetic fields.
• Apply these concepts to real-world scenarios in Ghana.

Lesson summary

This lesson introduces a fundamental concept in electromagnetism: the force experienced by a moving charged particle when it travels through a magnetic field. We have all seen magnets attract and repel objects, but the magnetic force can also act on invisible, moving charges like electrons and protons. This principle is not just an abstract idea; it is the engine behind many technologies we use in Ghana. From the way old "box" television sets created pictures on the screen to the sophisticated medical imaging machines in our major hospitals like Korle-Bu, understanding this force is key. It also explains how the Earth's own magnetic field protects us from harmful solar radiation.

Lesson notes

2.1 The Origin of the Magnetic Force on a Charge

A magnetic field is a region of space where a magnetic force can be detected. We know that magnets and current-carrying wires create magnetic fields. A key discovery in physics is that: A stationary electric charge feels NO force from a static magnetic field. A moving electric charge CAN experience a force from a magnetic field.

This force is often called the magnetic Lorentz force. It is a unique force because it only acts on charges that are in motion relative to the magnetic field. 2.2 Factors Affecting the Magnetic Force

The magnitude of the force (F) experienced by a charged particle depends on four main factors, as highlighted in the NaCCA exemplar: Magnetic Field Strength (B): A stronger magnetic field exerts a greater force. The magnetic field strength (also called magnetic flux density) is measured in Tesla (T). Magnitude of the Charge (q): A particle with a larger charge (e.g., an alpha particle with +2e) will experience a greater force than a particle with a smaller charge (e.g., a proton with +1e), all other factors being equal. Charge is measured in Coulombs (C). Velocity of the Particle (v): A faster-moving particle experiences a greater force. If the particle is not moving (v=0), the force is zero. Velocity is measured in metres per second (m/s). Angle of Motion (θ): The angle between the particle's velocity vector (v) and the magnetic field vector (B) is crucial. The force is maximum when the particle moves perpendicular (at 90°) to the magnetic field lines (`sin 90° = 1`). The force is zero when the particle moves parallel (at 0°) or anti-parallel (at 180°) to the magnetic field lines (`sin 0° = 0`, `sin 180° = 0`). 2.3 The Formula for Magnetic Force

Evaluation guide

• Explain f orce on a moving charged particle in an electric field.
• Experiential Learning: Using video simulations explain the main factors that affect charged particle s
• moving in the magnetic field i.e., the direction of the field, the direction of the particle and the charge of
• conceptual