IP Topics

01 September

Newton’s Nightmare

Seng Kwang Tan 18 Electromagnetic Induction, Demonstrations, IP4 16 Electromagnetic Induction 0 Comments

This demonstration is called Newton’s nightmare because it involves the slow dropping of a magnet that seems to be inconsitent with gravitational acceleration.

Using the “CFILE” structure, we can explain how the magnet moves much slower in a metal pipe than when it is undergoing free fall (as in the PVC pipe, which serves as a control).

Now, the metal that we use cannot be ferromagnetic, or the magnet will not even drop at all. It will simply be attracted to the pipe and stick to it.

However, if another metal such as copper or aluminum is used, as the magnet moves through the pipe, different sections of the pipe will experience either a change (either decreasing or increasing) in magnetic flux. Sections of the pipe that the magnet has just gone through suffers a decreasing flux while those that the magnet are approaching gains magnetic flux.

By Faraday’s law, which states that an induced emf is proportional to the rate of change of magnetic flux linkage, emf and hence, current is induced within the pipes. These induced currents are called eddy currents.

By Lenz’s law, the induced currents tend to flow in a way so as to oppose the change causing it. The current in the sections of the pipe that the magnet is leaving will trying to attract the magnet while those that the magnet is approaching will try to repel the magnet.

The effect is that the magnet experiences a retarding magnetic force that acts against gravitational force, hence decreasing its downward acceleration.

01 September

Diamagnetism

Seng Kwang Tan 16 Electromagnetism, Demonstrations, IP4 14 Magnetism 0 Comments

I didn’t want to spend money on buying a piece of pyrolytic graphite and large neodymium magnets so I made do with what I have to make the following video. While diamagnetism is not in the A-level physics syllabus, it’s good for students to know that there are other classifications of magnetic materials.

What we study in our syllabus is ferromagnetism, which is exhibited by materials such as iron, cobalt and nickel. Some pencil leads are paramagnetic (weakly attracted to magnets) while others such as the one in the video are diamagnetic (repelled by magnets).

I bought my neodymium magnets from DX.com and the shipping to Singapore takes about 3 weeks, so you might want to factor that time in if you want to get some for your lessons. These magnets are great for other demonstrations such as homopolar motors and Newton’s nightmare.

15 August

Introducing Delight! An Educational Board Game on Current Electricity

Seng Kwang Tan 15 DC Circuits, Featured, Games, IP4 12 DC Circuits, IP4 13 Practical Electricity, Teaching Resources 0 Comments

Delight - Physics board game on electricity

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Creative Commons License
Delight by Tan Seng Kwang is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

An educational board game for 2 or any even number of players (in 2 teams) based on the concepts of current electricity. Targeted at high school / junior college physics students, Delight is a fun way of practising the use of physics concepts such as

  1. electrical power $$P=\frac{V^2}{R}$$
  2. the potential divider rule.
  3. wires bypassing a device short-circuits it.

This game can be easily printed on A4 paper and the game pieces can be cut up for use.

Game Play

  1. This game is meant for 2 players or 2 teams of players. Each player/team has the following tiles:
    • 2 x light bulbs
    • 3 x T-shaped wires
    • 2 x crossed wires
  2. The players will take turns to place the tiles on the board.
  3. Each new tile must have at least one wire connected to an existing wire on the board.
  4. The game will end when the last tile has been placed on the board.
  5. The person with the brightest bulb will win.In the event that there is an equal number of opposing bulbs of the same brightness, it will be considered a tie. If there are three bulbs of the same brightness, the one with two of these bulbs wins.

Test Yourself: Who is the winner for the games below?

GAME 1

delightend

GAME 2

gameplay2

 

 

 

Conditions for Using this Game

  1. Anyone can print and use this game for free as long as it is for educational or personal use. Any other reproduction or republishing of this material, in hard copy or electronic form, without written permission, is prohibited.
  2. If you would like to make a suggestion or an enquiry, please leave a comment below.
08 May

Learning about Sound with Audacity

Seng Kwang Tan 11 Wave Motion, IP3 08 General Wave Properties (Sound), Teaching Resources, Technology

Audacity is a free audio recording and editing software downloadable from http://audacity.sourceforge.net. It is cross-platform meaning you can run it on PC or Mac.

Once you have the software installed, you can try out some of its simpler functions, such as recording and playing back. You can also generate tones of known frequencies, which will be useful for experiments such as using stationary waves to determine the speed of sound in air.

Frequency and pitch

The first activity serves as an introduction to the software and can be easily carried out. All you need is a computer with Audacity installed and a microphone connected to it. Tuning forks of different frequencies will be best for this activity because of the simple and pure waveforms generated. A regular wave pattern can also be recorded with the help of a musical instrument such as a guitar or by singing a note.

To make a sound with the tuning fork, strike it against something hard such as the heel of your hand. The two prongs of the fork, known as “tines,”  will then vibrate with a fixed frequency, thus generating a waveform with a displacement that is almost sinusoidal. Place this tuning fork next to the microphone and you should see a densely packed waveform like the following:

using-audacity-to-learn-about-sound

Zoom into the peaks recorded by clicking on the peaks of interest and pressing Ctrl 1 for Windows or Command 1 for Mac. You should observe a repeated pattern in the waveform.

audacity-sound-experiment

By reading off the time difference on the horizontal axis between two peaks, you can measure the period of the wave. Using $$f=\frac{1}{T}$$ where f is the frequency of the wave, and T is the period, you can verify the frequency measured with the known value of the tuning fork’s frequency.

In the above graph, the period is 2.8190-2.8155 = 0.0035s. The frequency of the tuning fork used is given by $$f=\frac{1}{T}=\frac{1}{0.0035}= 286 \text{ Hz}$$ which is roughly that of a D note.