Insight 2010 Exam [Questions]

[Linkage1992]

Oh boy, i seem to be digging myself into a deeper hole. i don't know what the hell to think now.   

[d-ea-6]

LOL.

All you have to do, mate, is say that Insight are wrong. And we can put this to rest

[Linkage1992]

yeah, i'll probably talk to my teacher about it. what a fucked up question.

[cjw]

hey, i get what your saying, but how can you multiply the whole area by 3, if it is only the rod that has extra lengths in it and not the horizontal rails?

[3Xamz]

This is true according to iTute;

If a 10 cm conducting wire moves 5 cm horizontally across a magnetic field;
The the change in area is given by 10cm*5cm = 50cm^2

This will provide an induced EMF, and also produces a current according to Lenz's Law.

This supports what Linkage was saying earlier; but not to the part where he said no current is produced. According to iTute there is indeed a current along the moving wire? :S

[d-ea-6]

This is true according to iTute;

If a 10 cm conducting wire moves 5 cm horizontally across a magnetic field;
The the change in area is given by 10cm*5cm = 50cm^2

This will provide an induced EMF, and also produces a current according to Lenz's Law.

This supports what Linkage was saying earlier; but not to the part where he said no current is produced. According to iTute there is indeed a current along the moving wire? :S

This is only relevant to question 4. Like I said earlier, the rods are stationary in question 3 when the magnetic field is switched off.

But, if you'd like, we can look at question 4 and find that it works as follows:

emf = nBlv = 3 x (30/1000) x (30/100) x (5/100) = 1.35x10^-3 V
Alternatively:
emf = nΔBA/Δt = (3 x (30/1000) x ((15/100)x(30/100))) / 3   =  1.35x10^-3 V     (3 is obtained by using t=d/v = 15cm/5cms^-1 = 3seconds)

[3Xamz]

Oh yes of course!
So, question 3 is not do-able?
Because its a wire thats not moving, so we don't have a change in flux ?

[d-ea-6]

Question 3 is not do-able because we don't know the area. The change in flux is 30x10^-3 T x area (as a result of the magnetic field being switched off).

Hypothetically, let's just say that the width of each rod was 2cm. Then it'd just be a standard emf question which you'd answer by doing as such:

emf = nΔBA/Δt = (3 x (30/1000) x ((30/100)x(2/100))) / (6/1000)  = however many volts

That's how I see it.

Edit: Yes, my mistake

[3Xamz]

Yup, that's how I see it too.

Except;

"The change in flux is (30x10^-3)*AREA"

[Linkage1992]

This supports what Linkage was saying earlier; but not to the part where he said no current is produced. According to iTute there is indeed a current along the moving wire? :S

well that's what i initially thought because it said conducting rails, so i assumed there was a current running  along both of them. But then when dea6 started suggesting otherwise, I realised that the rails weren't actually connected to anything so I started doubting myself. It really is an ambiguous question.

[SixWinged]

The question is do-able if you make some assumptions. Since there is only one vertical and one horizontal measurement given, it's pretty clear that the area will be the product of those two, even if the diagram doesn't support it.

Anyway, I agree, Insight 2010 was ridiculous, they tried to make it hard and couldn't even do basic maths themselves. So many errors in their solutions.

[jpcauchi]

LISTEN, point is, the 2010 insight exam is the worst physics exam i have ever come across, and it's my 17th unit 4 practice exam. It is riddled with errors and many of the solutions are ... simply wrong

[shokstar]

LISTEN, point is, the 2010 insight exam is the worst physics exam i have ever come across, and it's my 17th unit 4 practice exam. It is riddled with errors and many of the solutions are ... simply wrong

Are you referring to the last two questions? Cos they are unbelievable. Are the correct answers 150ohm for q17 and 54000J for q18?