[DOWNLOAD] My Half-Yearly Examination (3 Viewers)

[someth1ng]

I should read the question properly (I was just skimming). I'll have a look later.

If it did say EMF in the coil, then it would be AC since the coil would act like an AC generator.

 

[anomalousdecay]

One thing I've learnt from this: I need to read and analyse questions a lot more carefully.

+1000000

 

[iBibah]

Here's what I was thinking. Since when t=0, V=0, the plane would initially be perpendicular to the direction of the magnetic field. If you turned it clockwise or anti-clockwise, the induced current would be induced in the same direction using right hand rule, and so as you said by Faraday's Law, the induced voltage should not change direction. Therefore, our answer would be A, if that makes any sense.

That's incorrect though. If you turn it one way, according to Lenz's Law, an EMF will be induced to create a current that generates force to oppose the original motion. By what you have said (if either direction of rotation occurs a current is generated in the same direction regardless) one of the ways would violate the law of conservation of energy as the current would be in the direction of rotation and you would generate infinite energy.

These diagrams shows the direction the sides are moving at each point in rotation. Reversing rotation would revise direction.

 

[bleakarcher]

That's incorrect though. If you turn it one way, according to Lenz's Law, an EMF will be induced to create a current that generates force to oppose the original motion. By what you have said (if either direction of rotation occurs a current is generated in the same direction regardless) one of the ways would violate the law of conservation of energy as the current would be in the direction of rotation and you would generate infinite energy.

These diagrams shows the direction the sides are moving at each point in rotation. Reversing rotation would revise direction.

I get what you're saying man but do you mind explaining how you could deduce it using the right hand grip rule? I tried using that and got a result that violated the law of conservation of energy lol.

 

[RealiseNothing]

Yer question 11 is B.

 

[RealiseNothing]

I think you can use the formula to see that as the loop rotates in the opposite direction, the velocity of the coil is in the opposite direction and hence the induced EMF will change from positive to negative etc.

Also another way to think of it is that the current induced will reverse every half-turn, and so the induced EMF has to reverse every half-turn.

 

[iBibah]

I get what you're saying man but do you mind explaining how you could deduce it using the right hand grip rule? I tried using that and got a result that violated the law of conservation of energy lol.

In this case to deduce it using the right hand *palm rule you cannot consider it at that point.

Here are the two cases:

Ignore the graph for now, and consider the framed diagrams:

LEFT:

LK is moving clockwise, hence when the plane is parellel to the magentic field, it will be moving downwards. To oppose that motion, a current will be generated such to make it move up, and now we use the right hand palm rule to deduce that the current must run from K to L in order to oppose the motion.

RIGHT:

LK is moving anticlockwise, and will also being moving downwards when the plane is parallel. To oppose that motion the current will flow from K to L.


Now even though they are the same in direction at this point, they are still in different half-turn's. So when LK reaches Y (on the right picture), the current will in fact be moving from L to K (using RHP rule).

Consider the graph now:

So in half-turn 'A', they are going different directions, hence one is negative of the other. Hope that makes a little more sense.

 

[bleakarcher]

Thanks for that man, appreciate it. Just one final thing, what's wrong with this? There must be something wrong with the direction of the induced magnetic field but it's not clear to me.

 

[Hypem]

Thanks for that man, appreciate it. Just one final thing, what's wrong with this? There must be something wrong with the direction of the induced magnetic field but it's not clear to me.

View attachment 28045

I'm pretty sure the current on that first diagram is going the wrong way.

If you use the RHP rule - the right side of the coil is being pushed downward, so you switch your palm to make the force upward and the current travels down on the right side, not up.

 

[iBibah]

"Using the Right-Hand or Left-Hand Grip Rule, Please write your name neatly in the box above."

 

[Fizzy_Cyst]

Awesome to see all the intense debating the MC has caused!

MUAHAHAHAHA

I hope my classes are as intense!

 

[Fizzy_Cyst]

but with Q 7, in hsc isnt friction ignored, so shudnt answer be C?
i know in reality friction will affect

Orbital decay is definitely in the syllabus

Whilst you would never be asked to use in terms of quantitative analysis, you are expected to 'account for orbital decay', this is really just that.

 

[hayabusaboston]

Orbital decay is definitely in the syllabus

Whilst you would never be asked to use in terms of quantitative analysis, you are expected to 'account for orbital decay', this is really just that.

How deep do u think a question on orbital decay could possibly get? not more than 4 marks surely?

 

[RealiseNothing]

How deep do u think a question on orbital decay could possibly get? not more than 4 marks surely?

I think it's possible that you could get a long response on it such as "assess the impact of varying atmospheric densities on space travel and satellite navigational systems".

I'd say that's worth atleast 6 marks.

 

[anomalousdecay]

I think it's possible that you could get a long response on it such as "assess the impact of varying atmospheric densities on space travel and satellite navigational systems".

I'd say that's worth atleast 6 marks.

Yeah but a question like that does not assess a students FULL knowledge towards space travel.
Rather, a 6 marker would be something like:

"Discuss the issues involved with orbiting and re-entering Earth's atmosphere on space travel and satellite navigation systems."