2011 GCE O Level Physics (Pure) Paper 1 Suggested Solutions

冷风1985

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Combined Chemistry Paper 1 (MCQ)      Combined Science Paper 2 (Physics)      Combined Science Paper 3 (Chemistry)

冷风1985

Reserved for explanations.

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[Q23]

In the above diagrams, the orange colored rays indicate the orginal direction of light. Compare the orange colored rays with the refracted rays on the right, you will notice that only in A, light beams become more converging.
这个题目其实稍稍有一点超纲. 不过, 从converging lens这个名称上, 应该可以判断出来"光透过这种透镜后, 会变得更加汇聚".
For further understanding (this explains why a lens of convex surfaces (凸面) is always a converging lens):

Note: every time when refraction occurs on the intermedia surface, incident angle/refracted angle in the glass will be smaller than the refracted/incident angle in air.
Following this law, you can also explan using graph, why diverging lenses always have concaved surfaces (凹面).

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[Q33]
Question:  A person touches the live wire. Will it cause the 3A fuse to blow?
Answer:    No.
Explanation:The resistance of a human body ranges from a few hundred ohms (wet condition) to a few hundred kilo-ohms (dry condition). So the current will be less than 3A. The fuse will not blow.

Refer to the following table: you will notice that a current that causes death is actually quite small, only 0.1~0.3A

Current	Effect
1mA	Threshold - no pain below this point
5mA	A frightening but harmless shock
10 -20mA	Uncontrolled muscular contractions Loss of muscle control - you cannot let go
50mA	Pain and exhaustion; breathing affected
100 - 300mA	Uncoordinated contraction of the heart leading to death

shichuanhua

16should be c

冷风1985

shichuanhua 发表于 11-11-2011 14:12
16should be c

you are correct. I thought its asking about the vacuum.

shichuanhua

I dont get question 37 :X ughhh stupid sia , I lost 7 marks :'(:'(

云海儿

Q33 起了很多议论。
有 B/C 的答案 x.x
我也是搞不清楚。。

冷风1985

qwe561187 发表于 11-11-2011 17:35
33   should be C?
A person touches the live wire
The live wire touches the neutral wire

The resistance of a human body ranges from 300 - a few k ohms, so for a mains voltage of 230V, the current is less than 1A, will not cause the 3A fuse to melt.

taxy

why 23 cannot choose c?

你猜

冷风1985 发表于 11-11-2011 21:22
The resistance of a human body ranges from 300 - a few k ohms, so for a mains voltage of 230V, the  ...

If the person`s hand is wet,the resistance of the person would be very low,then the statement is possible.Right?

冷风1985

你猜 发表于 12-11-2011 00:50
If the person`s hand is wet,the resistance of the person would be very low,then the statement is p ...

if the person is wet, resistance will also be a few hunderd ohms.