Q&A - PSLE Science
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Chenonceau:
A coin or a nail will allow current to flow through as easily as a wire. Therefore, if we connect a coin or a nail in parallel to a bulb, the bulb will not light up because current will only flow through the coin or the iron - the bulb is short-circuited.
Can I bother you to explain a bit more?atutor2001:
Incidentally, I think coin and nail have very low resistance and will cause short-circuit. -
atutor2001:
A coin or a nail will allow current to flow through as easily as a wire. Therefore, if we connect a coin or a nail in parallel to a bulb, the bulb will not light up because current will only flow through the coin or the iron - the bulb is short-circuited.[/quote]Ok thank you. So, you weren't referring to Pixiedust's earlier question right? Because that question did not have the coin and nail in parallel...
Can I bother you to explain a bit more?Chenonceau:
[quote=\"atutor2001\"]
Incidentally, I think coin and nail have very low resistance and will cause short-circuit. -
Chenonceau:
Right. Apology for giving confusing feedback.
Ok thank you. So, you weren't referring to Pixiedust's earlier question right? Because that question did not have the coin and nail in parallel... -
atutor2001:
Nah... no harm done.
Right. Apology for giving confusing feedback.Chenonceau:
Ok thank you. So, you weren't referring to Pixiedust's earlier question right? Because that question did not have the coin and nail in parallel...
I learnt something except that my son had to calm me down and explain carefully a few times that parallel thingy because I kept telling him that he was wrong on Pixiedust's question. But that's ok. My DS learns when he has to explain to his Idiot Mom. -
you’re welcome, atutor2001, Chenonceau.
Thanks for pointing out the nail and coin. I thought there might be impurities in the nail and coin and thus increase their resistance. I’ll take it out of the explanation. -
Fat Mama:
actually, both of us are correct. It's just a matter of perspective.
Just to clarify as I am not v gd at circuits. DD's teacher said electricity flows from -ve to +ve pole. However in ur diag, the current flows from +ve to -ve. So who is correct?
Your child's teacher is explaining it from the perspective of physical subatomic particles. Current is caused by the travel of electrons, which move from the negative terminal to the positive terminal. However, when the current flow is drawn on paper, the convention is to draw from + to -. This is because at the time when electricity was first discovered, scientists did not understand the atomic model and electrons were not really understood. They actually thought that electricity was caused by the flow of positive particles. However, that convention of current flow has stuck to this day, so they now say that current flow is opposite to electron flow.
Just take note that when drawing current flow on paper, it is from positive to negative. When explaining it from a particle viewpoint, the flow is from negative to positive.Fat Mama:
when analysing circuit diagrams, you have to look at it segment by segment. You can't look at the entire electrical path because of the different segments the current flows through. What is a segment ? it is a path delineated by two junctions. A junction is where the path forks into 2 or more paths. So you can't really compare resistance of B1,B2 and B4 with B2 and B3 because there are all on different segments. It is a bit difficult to explain with words, diagrams would be very helpful here to give you an example. I'll see if I can come up with something.Is it right to say B1, B2 n B4 are connected in series? B2 n B3 are connected in parallel. So resistence of B1, B2 n B4 are greater that B2 n B3 so the current flows to B2 n B3?
Fat Mama:
you need to look at resistance on a segment by segment basis. Maybe later I'll see if I can explain in more detail. kinda rushed right now.U said LM and GH with no device on it's path, but isn't B3 connected to LM and GH?
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Much appreciate your help, cimman !
I am not getting 100% yet, need to digest digest, drink more coffee !
Hopefully my son can help me out later....
About the flow +ve to -ve, yup agree with cimman, I've also asked a similar question earlier in this thread as I was confused by the point raised in a PSLE science guide book (MC). -
Can somebody please advise if the topic on Simple Machines (lever, pulley and gears) is out of the PSLE syllabus. I observe questions on this topic appeared in the 2009 top school exam papers, but not anymore in the 2010 exam papers.
Also, where can one get the 2011 top school exam papers, other than buying from the stands I see around shopping malls. The printing is often poor.
Thank you. -
anneshirleygilbert:
Yes, simple machines is out of PSLE syllabus. The sun, moon and the universe is out too.Can somebody please advise if the topic on Simple Machines (lever, pulley and gears) is out of the PSLE syllabus. I observe questions on this topic appeared in the 2009 top school exam papers, but not anymore in the 2010 exam papers.
Also, where can one get the 2011 top school exam papers, other than buying from the stands I see around shopping malls. The printing is often poor.
Thank you. -
You can get exam papers from websites.
Like this one here:
http://www.misskoh.com/
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