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Common Science Mistake

March 28, 2014

After Science CA1, we looked through and analysed the papers of the students and there are some mistakes that most students get it wrong over and over again in PSLE science across all P4, P5, P6 students.
We have decided to share them with you and may the mistake / misconception get recified once and for all.  PSLE A* Science for the win!
For a better view of the questions and answers, you may download the documenthere.
Feel free to post your questions to us if you have any. 🙂
Common Mistake 1
Topic: Matter (Primary4 Science)
An air pump is used to pump air into a tank through an inlet as shown below. The tank and air pump have a capacity of 500cm³ and 150cm³ respectively.
Kaizer added 200cm³ of water into the tank.
He then pushed the plunger of the air pump 5 times.
What is the volume of air in the tank now?
Mistake: 750cm³
Misconception: (amount of air in air pump – 150 cm³) X (5 times) = 750cm³
Actual Answer: 300cm³
Explanation: Water has a definite volume and occupies 200cm³ of space in the tank.
The remaining volume will be taken up by air which is 300cm³ as air has no definite volume and can be compressed.
Common Mistake 2
Topic: Water Cycle (Primary 5 Science)
When the water boils, a ‘white mist’ is seen off the kettle’s mouth. What is the ‘white mist‘?
Mistake: The ‘white mist’ is steam.
Misconception: white mist = steam
Actual answer: The ‘white mist’ is tiny water droplets.
Explanation: Steam is in gaseous state and gas can’t be seen. 
The steam from boiling water loses heat and condenses onto cooler surface provided by surrounding air forming tiny water droplets, such as mist.
Common Mistake 3
Topic: Magnets (Primary 4 Science)
The diagram belows shows 3 discs A, B and C.
     [  C  ]
     [  B  ]
 __[  A  ]__
Which of the follow above disc(s) is/are definitely magnet(s).
Mistake: B and C.
Misconception: Disc that repel are magnets
Actual Answer: C only
Scenerio 1: Disc A could be the magnet and Disc B, the non-magnetic material.
Magnetism can pass through non-magnetic material B and repulsion between like poles of A and C could occur.
Scenerio 2:  Disc B could be the magnet and A, either magnet/magnetic material or non-magnetic material.
Like poles of B and C could repel.
Thus we can only be sure that C is definitely magnet but not A and B.
Common Mistake 4
Topic: Light (Primary 4 Science)
How is shadow formed?
Mistake: Shadows are formed when an opaque object blocks the light.
Remarks: This is usually a 1-mark question. It requires 2 key points. The above answer only gives 1 and its half correct.
Actual answer: Light travels in a straight line and is blocked by opaque or translucent object.
Common Mistake 5
Topic: Light (Primary 4 Science)
A policeman was driving a patrol car and saw a tree behind him using the rear view mirror in his car.
Using lines and arrows, explain how the policeman was ableto see the image of the tree on the rear view mirror.
Mistake: Wrong direction of arrows. *We do not have Cylops eyes to give out light*
Forgets about the rear  view mirror.
Actual Answer: 1st Arrow: From Light source (sun) to object (tree)
2nd arrow: From object (tree) to Reflective surface (Mirror)
3rd arrow: From reflective surface (Mirror) to person (Eye).
Explanation: 1st arrow is always FROM light sources as it gives out light.
Light falls onto objects and reflect INTO our eyes.
Thus last arrow is always INTO the eyes.
Common Mistake 6
Topic: Light (Primary 4 Science)
Aaron set up a light sensor to count the number of identical cans on a moving belt.
The belt moves at the same speed. As the cans pass between the light source and the sensor, they block light from reaching the sensor. The data recorded is shown in the graph below.
Brightness Level
|   __    __     __
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|   |   |   |   |   |   |
|_ |_ |__|_ |__|__|____ Time (min)
How many cans could be counted in 5 minutes
Mistake: 2
Misconception: Students count the bar
Actual answer: 3
Explanation: The object will block the light. The part of graph WITHOUT any brightness shows that there is an object.
Thus we count the spacing instead.
Common Mistake 7
Topic:  Forces (Primary 6 Science)
The diagram below shows how a ball travelled across a school field when it was thrown from point X. .
                          [X] (ball)
Draw bar graph to show the correct amount of gravity acting on the ball at point , X, Y and Z.
Amount of Gravity
|________________ Time
    X        Y        Z
Mistake: Student draw a graph showing Y has the highest amount of gravity and Z the lowest amount of gravity.
Misconception: Student thought that the question is asking for gravitational potential energy.
Amount of gravity IS NOT EQUAL to gravitational potential energy.
Actual Answer: The bar graph for point X, Y and Z should be at the same height.
Explanation: Amount of gravity on earth isthe same irregardless of heigh which the ball is at.
Do you have any questions to ask? Feel free to contact us.

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