This blog is managed by Song Hock Chye, author of Improve Your Thinking Skills in Maths (P1-P3 series), which is published and distributed by EPH.

## Friday, November 16, 2007

### The Consequential Question Trap

“The challenge, and it is often a difficult one, is for the question setter to pose the question in such a way that pupils with widely different background experiences will all build a sufficiently common mental picture and that mental picture is the same as the question setter’s mental picture”Associate Prof Boo Hong Kwen, NIE (Straits Times Forum, 15 Oct 2004), commenting on the difficulty level of the PSLE 2004 Science Paper.

Question for students is, do you have a mental picture that is the same as the question setter’s mental picture?

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THE CONSEQUENTIAL QUESTION TRAP -
Why you should know what is in the question setter’s mind behind that Science question

Some students are puzzled, why they are marked wrong for certain Science questions, when the answer they give is right. This usually occurs when a set of questions is tied to a certain understanding of a theory.

A typical question (like the one illustrated below), is subdivided into Part (a) and Part (b). In this particular example, Part (a) tests on application of a theory, while Part (b) tests on knowledge of the theory itself.

In such an instance, if Part (a) is answered wrongly, Part (b) will also be marked wrong, regardless if the answer in Part (b) is answered correctly or not. The reason is because if the student gets Part (a) wrong, it tells the examiner that he/she does not understand the topic at all.

As such, even if Part (b) is answered correctly, it simply gives the examiner the impression that the student has probably just memorised the answer by heart, without understanding the theory involved.

Such a question is dubbed, The “Consequential Question Trap". It is considered a “trap” because students who learn science “by heart”, will usually fall for this kind of “trap” questions.

Below is an example of a typical “consequential question”, where Part (b) is dependent on Part (a). This example is a question taken from Primary 5 syllabus. The topic is “Electricity”.

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Question
The diagram below shows four objects A, B, C and D connected to an electric circuit.

a) Which bulb(s) will light up?
b) What conclusion can you give regarding objects A, B, C and D?

a) Bulbs 1, 2 and 4 only.
b) Steel rod and metal rulers are conductors of electricity, while rubber and plastic rods are not.
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Part (a) tests the student’s application of theory, as to what are the consequences if you place a conductor or an insulator in an electrical circuit.

Part (b) tests on student’s knowledge on the characteristics of conductors and insulators.

To be able to answer Part (b) correctly, you must be able to identify which bulbs light up in Part (a).

If the student gets Part (a) wrong, it gives examiners the idea that he/she does not understand that the conductors will form a closed electrical circuit, resulting Bulbs 1, 2 and 4 to light up - while insulators will break the circuit, causing Bulb 3 to remain unlit.

From here, we can see that if Part (a) is answered wrongly, and if the student proceeds to answer Part (b) correctly, the impression given to examiners is that, the student has probably learnt by heart that “metals are conductors of electricity while plastic and rubber are not” in Part (b) - without understanding the theory that conductors conduct electricity, while insulators break the electrical circuit.

The above being the case, examiners will be highly suspicious as to how the student answered Part (b) correctly, when Part (a) has been answered wrongly!

A “consequential question” hence, has to be answered correctly from the start. If the initial part is answered wrongly, the subsequent answer(s) will be marked wrong, regardless how they have been answered.

The only way to get all parts right, is to study and understand its theory.

Learning “by heart” will not help!
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The above article was published in Excel!, a publication of Excel Eduservice in Oct 2004.
Publication Permit No: MITA (P) 297/03/2004

keentolearn said...

Dear Mr Song

Sarah wants to find out whether the voltage of batteries used in a circuit affects the brightness of a bulb. To ensure a fair test, the number of batteries and the length of wires are kept constant. Besides changing the voltage of batteries, one of the variables that she should change is the voltage of the bulb. Please help to explain why we need to change the voltage of the bulb?

Excel Eduservice said...

Where did you get the question from? If you want to test if a change in the voltage of the batteries will affect the brightness of the bulb, ALL other factors must be kept constant.

I cannot think of a logical answer why there is a need to change the voltage rating of the bulb.

keentolearn said...

Dear Mr Song
Thank you for your reply.I am sorry, I can't remember the source where I read the question from.I do hope I remembered the facts correctly.

Will inceased voltage of batteries blown up a bulb rated at lower voltage? For example a light fitting rated at 24V ac needs a transformer when installed in a 230Vac circuit.I am not sure about bulb in a dc circuit.

Excel Eduservice said...

It does not matter if it is an AC or DC circuit. If the bulb voltage rating is lower than the voltage of the circuit, there is a good chance the bulb may blow.

Incidentally, AC circuit is not part of PSLE Science syllabus.

keentolearn said...

Dear Mr Song,

Going back to the Sarah's question, can we now say that the voltage of the bulb should be changed to correspond with the increase in batteries' voltage.This is to prevent the bulbs from being blown.

Excel Eduservice said...

Yes, a the voltage rating of the bulb must be the same as the voltage of the circuit.

If the voltage rating of the bulb is lower than the voltage of the circuit, the bulb may blow.

If the voltage rating of the bulb is higher than the voltage of the circuit, the bulb may not light up to its optimum performance, because the voltage of the circuit will not be able to "power up" the bulb to its "designed brightness".

That means, you wasted your money on that over-rated voltage bulb.

keentolearn said...

Dear Mr Song

Upper primary students will certainly benefit if they read your input diligently.

A big Thank You.

Anonymous said...

The weak / average students tend to be careless. Due to their carelessness, they may answer part a wrongly. Hence to mark part b wrong when the answer is correct does not sound fair to them.

Anonymous said...

What if you get part (a) right but part (b) wrong, would you get the marks for part (a)?

Excel Eduservice said...

Yes, you will score for part (a).

pls help me said...

Hi um could someone help me pls?

Sophian set up an experiment to find out the products of alcoholic fermentation.He boiled the glucose solution and cooled it.Then he added yeast cells.Next,he poured a thin layer of liquid parrafin on top of the glucose solution.He observed that the limewater turned cloudy when the set-up was left in a warm place after an hour.

Anonymous said...

Hi um could someone help me??

Sophian set up an experiment to find out the products of alcoholic fermentation.He boiled the glucose solution and cooled it.Then he added yeast cells.Next,he poured a thin layer of liquid parrafin on top of the glucose solution.He observed that the limewater turned cloudy when the set-up was left in a warm place after an hour.