Physics paper 1

[waleedsmz]

Question 34: http://www.xtremepapers.me/CIE/index.ph ... _qp_11.pdf

What exactly is the plastic support? My answer was A but it turned out to be C. I thought that the plastic insulates the current.

Another thing is why A is not correct. I mean won't the current pass through the metal in this situation?

Thanks.

 

[cHeStEr]

It is under an metal which is nit earthed..so current can pass thru metal into the wire so one can get a shock when touching !

Idea that states .. Improper earthing of wire can pass a shock .. Should be kept in mind !

I hope this things helps !

Best of luck @9

 

[Rahma Magdy]

I couldn't really get why A isn't correct :S

 

[amaghraby]

plastics do insulates current....this will be true if the person touches the plastic but in this question the person touches the metal case which is a conductor

 

[amaghraby]

plastic support simply means that the metal case is placed on a plastic table or so

 

[waleedsmz]

Thanks so much dude. But I still don't know why A is incorrect... I mean the current would have to pass through the metal case to electrocute anyone right?

 

[mshaheen95]

look the for a current to pass through the circuit (i.e. the man) it needs to be closed.
so when someone touches the metal case the circuit is closed and the current is earthed through the mans body
but until it is touched (earthed) no current will pass
i hope u understand

 

[waleedsmz]

You mean that without anyone touching it, it will be assumed that the metal case is an opened circuit?

 

[mshaheen95]

yes with no current passing through it

Other useful cases:
there is an earth wire --> fuse in live wire will blow because a large current passes
no plastic support i.e. its in touch with ground --> fuse in live wire will blow