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23 May

Adiabatic Process Demonstrations

09 First Law of Thermodynamics, Demonstrations, Featured 0 Comments

Here are some interesting lecture demonstrations on adiabatic thermodynamic processes you can carry out. In an adiabatic process, there is no heat transfer between the system and other systems (including its environment.) According to the First Law of Thermodynamics ($$\Delta U=Q+W$$), where Q = 0, a compression of a gas which is associated with work being done on the gas will cause the internal energy and hence, the temperature of the gas to rise. On the other hand, when an expansion of a gas takes place, the gas will cool down.

1. Adiabatic compression using a fire syringe

(available from Funlearners for $30 in Singapore)

2. Adiabatic expansion using a fire extinguisher

19 September

P6 Science Question on Light Bulb

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This picture has been making its way around the internet. This is a Primary 6 Science question that has a questionable answer. As teachers, there are times when we make mistakes in crafting answers for a multiple-choice question. Good thing there is often a fail-safe in the form of our colleagues who would help each other vet the questions we set. Sometimes, despite all effort, mistakes are made such as this

Primary 6 Science Question on Light Bulb

The story according to the person who posted this:

This P6 science question is taken from a paper that is set by a local brand name primary school. The majority of the students who took this test gave the answer as (4). The science teacher insisted that the answer is (2). The reason given was that sentence D should be interpreted to mean that only light energy is given off when an electric current passes through it.

The children, as well as many other adults who are well versed in the English language, unanimously agreed that the students were correct to interpret the sentence as meaning that the bulb will give off light energy (though it does not rule out other forms of energy) only if an electric current passes through it (so if there is no electric current, the bulb will not give off light energy.

The HOD called to clarify that her teacher (and therefore the dept) is correct. She apparently said that there is nothing wrong with the statement, and that it is not meant to be read in an ‘English’ way, but rather in a ‘scientific’ way. She then proceeded to read the sentence aloud, pausing after the word ‘only’. When it was pointed out to her that there is a need for a comma after ‘only’ if it is to be read with a pause, she insisted that that was the ‘scientific’ way of reading the sentence, and went on to qualify that laymen would not be able to distinguish between the scientific reading and the English reading, but that the students, having studied the subject for four years, were expected to tell the difference. According to her, this would set the A* students apart from the A students.

Since when our English language developed a ‘scientific’ dialect?! And if you cannot apply standard English language rules to reading the questions of a paper set in English, then perhaps we need to clarify that the paper is written in Scientific-English instead? What kind of nonsense is this?

Many netizens have condemned the answer which was given by the teacher as (2) instead of (4), what made matters worse was the defence given by the HOD. I agree that the statement D could be better phrased as “It gives off only light energy when an electric current passes through it”, therefore making it a false statement and hence, not part of the answer.

This incident reminds us of the need to be careful in the way we phrase our questions, often re-reading them to see if they could be misinterpreted or if they could be made clearer.

15 August

Introducing Delight! An Educational Board Game on Current Electricity

15 DC Circuits, Featured, Games, 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.
04 January

Homopolar Motor 1

16 Electromagnetism, Demonstrations, Featured

A homopolar motor is a simple electric motor that does not require the use of a commutator. The electric current flows in a fixed direction within the wires of the motor. The following are instructions on how to construct this simple teaching tool that can be used to demonstrate how a motor works, as well as teach concepts such as Fleming’s left-hand rule and $$\mathbf{F}= I\mathbf{l \times B}$$.

Materials

  1. Copper wire (about 22 cm)
  2. Small neodymium magnets (1 or 2)
  3. 1.5 V AA-size battery
  4. Base with either another magnet or a iron surface, such as the head of an iron nail

Procedure

  1. Make a V-shaped bend in the middle of the copper wire, with about 0.5 cm on both sides of the V-shape. Bend the copper wire into a rectangular loop using the dimensions shown below. Homopolar Motor Diagram
  2. homopolar motor baseTip: You may use the edge of a wooden block as a guide to bend the copper wires at right angles. A pair of wooden blocks can also be used to flatten the rectangular loop if you press them together tightly with the loop in between.
  3. Mount the neodymium magnet(s) onto the magnet or iron base.
  4. Hook the wires at the base around the magnets.
  5. Place the AA-sized battery with the protruding end on the magnet(s).
  6. Complete the electric circuit by placing the V-shaped end of the rectangular loop onto the flat end of the battery and watch the loop spin.
  7. Be careful not to keep the current flowing for too long as the battery and wire can get very hot.

Science Explained

  1. A force acts on a current if it is placed in a magnetic field. This force is what causes the motor to spin about its axis.
  2. To apply Fleming’s left hand rule, observe from the diagram below how the magnetic field bends around the magnet and its direction with respect to the direction of current flow. How do you think the loop will spin?homopolar motor field lines

If you are having difficulty making this version of the homopolar motor, try the other design for the homopolar motor made using a screw.