A-level Topics

09 June

Temperature and Pressure of Gas

Seng Kwang Tan 08 Temperature and Ideal Gases, IP4 17 Kinetic Model of Matter, Simulations 0 Comments

This interactive HTML5 simulation models the behavior of gas particles in a fixed-volume container, allowing users to explore the relationships between temperature, pressure, and particle motion. Users can adjust the temperature using a slider, which directly affects the speed of the particles based on kinetic theory. As particles collide with the container walls, they briefly turn red to visually indicate wall interactions—collisions that contribute to pressure. A real-time pressure gauge on the side rises proportionally with temperature, consistent with the ideal gas law.

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500 K

According to the kinetic model of matter, gases consist of a large number of small particles (atoms or molecules) moving randomly and continuously in all directions. These particles have kinetic energy, which depends on temperature.

As temperature increases, the average kinetic energy of the gas particles increases. This means the particles move faster. Since pressure arises from particles colliding with the walls of the container, faster-moving particles collide more frequently and with greater force. These more energetic collisions result in a higher pressure on the container walls.

In a fixed volume, this explains why pressure is directly proportional to temperature (in kelvin), a relationship described by: P∝T
(if volume and number of particles are constant)

08 June

AC Generator Simulator

Seng Kwang Tan 17 Alternating Current, 18 Electromagnetic Induction, IP4 16 Electromagnetic Induction, Simulations 0 Comments
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An AC generator, or alternator, is a device that converts mechanical energy into electrical energy by means of electromagnetic induction. At its core, the generator consists of a coil of wire that is made to rotate within a magnetic field. This magnetic field is usually produced by permanent magnets or electromagnets positioned so that their field lines pass through the area enclosed by the coil.

As the coil rotates, it cuts through the magnetic field lines. This motion causes the magnetic flux linkage through the coil to change over time. According to Faraday’s Law of Electromagnetic Induction, whenever there is a change in magnetic flux linkage through a circuit, an electromotive force (emf) is induced in the circuit. The faster the coil rotates or the stronger the magnetic field, the greater the rate of change of flux, and thus, the greater the induced emf.

The rotation causes the magnetic flux to vary in a sinusoidal manner, leading to an emf that also varies sinusoidally. This means the direction of the induced current reverses every half-turn, producing an alternating current (AC). The expression for the induced emf is typically given by: ϵ(t)=NBAωsin⁡⁡(ωt)

where N is the number of turns in the coil, B is the magnetic flux density, A is the area of the coil, ω is the angular velocity of rotation, and t is time.

To extract the current from the spinning coil without tangling wires, slip rings are connected to the ends of the coil. These rotate with the coil and maintain contact with carbon brushes, which allow the generated current to flow into an external circuit.

In essence, an AC generator works by continually rotating a coil within a magnetic field, causing a periodic change in magnetic flux that induces an alternating voltage. This principle is the foundation of electricity generation in power stations around the world.

07 June

Faraday’s Experiment Simulation

Seng Kwang Tan 18 Electromagnetic Induction, IP4 16 Electromagnetic Induction, Simulations 0 Comments
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In Faraday’s experiment, moving a magnet into or out of a coil induces an electric current, which is detected by a galvanometer. The faster the magnet moves, the greater the deflection of the needle. The direction of needle deflection depends on whether the magnet is moving toward or away from the coil—reversing as the direction of motion changes. When the magnet is stationary, the needle returns to the center, indicating no induced current.

This simulation allows the user to explore the laws of electromagnetic induction (Faraday and Lenz) by dragging a magnet into and away from a coil.

09 May

Fleming’s left-hand rule vs right-hand palm rule

Seng Kwang Tan 16 Electromagnetism 0 Comments

Fleming’s Left-Hand Rule and the Right-Hand Palm Rule are visual tools used to predict directions in electromagnetic interactions.

Fleming’s Left-Hand Rule applies to electric motors and helps determine the direction of the force (motion) on a current-carrying conductor placed in a magnetic field. By aligning the thumb (force, F), first finger (magnetic field, B), and second finger (current, I) at right angles, one can deduce the force direction.

The Right-Hand Palm Rule serves the same purpose, but might actually be more intuitive, as the fingers would look like parallel vectors in a uniform magnetic field. The thumb points in the direction of the current. The hand will then naturally look like it is exerting a push in the direction of the palm.

I like to joke with my class that both serve the same purpose but one resembles a gun while the other resembles a kungfu move. Which would you prefer?

Side note: The image above is generated using a single prompt with ChatGPT 4o: “draw an image representing fleming’s left hand rule, next to the right-hand palm rule.” I’m impressed by how far AI image generation has come.

05 April

Simulation of Projectile Motion with Air Resistance

Seng Kwang Tan 02 Kinematics, 03 Dynamics, IP3 03 Dynamics, Simulations 0 Comments
Open in new tab 🔗 This simulation offers a hands-on and dynamic way to explore the physics of projectile motion with and without air resistance. By adjusting parameters such as launch velocity, angle, and air resistance, users can visualize how these factors affect the shape and reach of a projectile’s trajectory. The app provides real-time changes including motion paths, velocity vectors, and a velocity-time graph showing horizontal and vertical components separately. It also calculates and displays key quantities such as maximum height and range under ideal and non-ideal conditions (based on an arbitrary coefficient of drag. Through interactive experimentation and visual reinforcement, learners gain a deeper understanding of concepts the effect of air resistance, and the difference between theoretical and real-world motion. This is suitable for JC1’s topic on projectile motion. It can also be used for Upper Sec, if you change the launch angle to 90 degrees.
15 March

Interactive System Schema Generator

Seng Kwang Tan 03 Dynamics, IP3 03 Dynamics, Simulations, Student Learning Space 0 Comments

I built this web app to help students draw system schemas, having blogged about this before.

It is also available and optimised for download for SLS.

Basic Instructions

To add Bodies:

  • Click the “Add Body” button.​
  • Click on the canvas to place the body at your desired location.​
  • Label the Body.

Add Forces:

  • Click the “Add Force” button.​
  • Click on two bodies that exert the force on each other.​
  • Label the Force.

Using System Schema to Understand Newton’s Third Law

Newton’s Third Law states that when Body A exerts a force on Body B, Body B exerts an equal and opposite force on Body A. While this principle is conceptually simple, many students struggle to apply it consistently across different physical scenarios. The System Schema approach provides a powerful way to visualise and analyse these interactions. It is a representation tool developed by The Modeling Instruction program at Arizona State University (Hinrichs, 2004).

A system schema is a diagram that represents objects (as circles) and interactions (as lines) between them. Instead of focusing on individual forces, a system schema helps students see the relationships between objects before applying force diagrams. This method emphasizes Newton’s Third Law by explicitly showing how forces come in pairs between interacting objects.

To correctly identify action-reaction force pairs, consider the following guidelines:​

  1. Forces Act on Different Objects: Each force in the pair acts on a different object. For example, if Body A exerts a force on Body B, then Body B simultaneously exerts an equal and opposite force on Body A.​
  2. Forces Are Equal in Magnitude and Opposite in Direction: The magnitudes of the two forces are identical, but their directions are opposite.​
  3. Forces Are of the Same Type: Both forces in the pair are of the same nature, such as gravitational, electromagnetic, or contact forces.

The steps to applying System Schema to Newton’s Third Law are as follow:

  1. Identify the bodies in the system – Draw each object as a separate circle.
  2. Represent interactions – Draw lines between bodies to indicate forces they exert on each other (e.g., a box on the ground interacts with Earth through gravitational force).
  3. Label force pairs – Each interaction represents an action-reaction force pair (e.g., a hand pushes a wall; the wall pushes back).
  4. By mapping forces this way, students can easily recognize that forces always act between bodies and in pairs, reinforcing the symmetry of Newton’s Third Law.

One of the most common misconceptions of students is that normal contact force and gravitational force acting on a body are action-reaction pairs because they are equal and opposite in a non-accelerating system. By using the system schema, they can see that the two forces involve interaction with different bodies, e.g. the floor of an elevator for normal contact force, and the Earth for gravitational force.