27-28 May SPA Key Sources of Error

NOTE: The key sources of error mentioned below are speculations. Also, do remember that in Physics SPA we are allowed to write as many answers as possible and they will give us marks for one correct answer. For Chemistry SPA, we are allowed ONLY ONE answer. Always remember to write what the errors lead to. It is advisable to rephrase the answers mentioned below to fit the context of the question in the actual exam.

Physics: (topic is Light)

-Involving mirrors
There is glass in between the area where the light ray strikes at the mirror and the silvered surface (where the light ray is reflected), leading to inaccurate angles of reflection recorded.

The mirror is light and is easily shifted by accident, leading to inaccurate drawing of lines for the light rays.

-Involving pins
The pin holes are too big for a pencil to pass through accurately, leading to inaccurate drawing of lines for the light rays.

When pins are required to be placed at the edge of the glass block or mirror, the pins cannot be placed exactly at the edge of the block, leading to inaccurate drawing of lines for the light rays.

- Involving lenses
The exact point where a clear image is formed cannot be defined exactly (for reasons similar to that of comparing colours to the colour comparison chart in Chemistry), leading to...

Chemistry: (topic is Metals)

This topic is somewhat difficult due to the broad scope of possible experiments. I will try my best to cover as many possibilities as possible

- Involving reaction of metals with time as a variable
The stopwatch cannot be started at the exact time when the reaction begins due to human reaction time (remember those experiments involving the small test tubes?), leading to inaccurate timings recorded.

- Involving reactions of metals with heat as a variable
There is heat loss to the environment, leading to inaccurate readings of temperature change in the solution.

It will be great if you guys could inform me of any other possible answers that I have missed out, and I will edit this post accordingly. Good luck, and feel free to ask questions.