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HSC Physics Marathon 2016 (1 Viewer)

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leehuan

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According to Faraday's Law a change in magnetic flux will induce emf as according to the formula emf = (ceebs latexing formula). As current does not reach maximum instantaneously, there is a brief building up period. According to the relationship B = kI/d, current is proportional to B, and hence as the current builds up (therefore changes) similarly there is a change in magnetic flux inducing emf on the phone. As the build up interval is very small, the change in magnetic flux would be very high and hence the repeated emf induced on the phone would be very high, which could lead to damage of the phone's internal components. This will occur both when the charge is turning on and when it is turning off, meaning that the emf is being repeatedly applied to the phone, potentially causing damage to the internal components.
An interesting thing to keep in mind is that the semiconductors (integrated circuits) in phones don't really want high voltages. Indeed though, correct
 

Drsoccerball

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An interesting thing to keep in mind is that the semiconductors (integrated circuits) in phones don't really want high voltages. Indeed though, correct
I think it's the opposite high voltages are better. If there is a low voltage the current is higher and thus has a higher chance of causing the semi-conductor to no longer possess its super conductive properties.
 

leehuan

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I think it's the opposite high voltages are better. If there is a low voltage the current is higher and thus has a higher chance of causing the semi-conductor to no longer possess its super conductive properties.
Typo here.
__________________________________

Isn't the input power what is technically constant?
 

Nailgun

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I think it's the opposite high voltages are better. If there is a low voltage the current is higher and thus has a higher chance of causing the semi-conductor to no longer possess its super conductive properties.
Does this mean my answer was wrong lol?
 

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Quick question:

A cannon shot was fired at an elevation angle of 40. A second shot was fired at the same speed, but at an elevation angle of 60. Compared with the first shot, what would the second shot expected to have:

A. shorter range
B. longer range
C. shorter time of flight
D. longer time of flight

I picked A, because if the 2nd shot was fired at the same speed but a higher angle wouldn't Ux be smaller (and hence range is smaller)? The answer is apparently D (not from textbook, just a teacher's answer)

Cheers
 

Drsoccerball

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Quick question:

A cannon shot was fired at an elevation angle of 40. A second shot was fired at the same speed, but at an elevation angle of 60. Compared with the first shot, what would the second shot expected to have:

A. shorter range
B. longer range
C. shorter time of flight
D. longer time of flight

I picked A, because if the 2nd shot was fired at the same speed but a higher angle wouldn't Ux be smaller (and hence range is smaller)? The answer is apparently D (not from textbook, just a teacher's answer)

Cheers
Worst question in HSC physics multiple choice...
 

loje

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Nah the answer is right.. but A is right as well.

Lel currently in the car and was bothered doing this bc bored if it makes it clearer hahaha.

(image clipped)
Thank you haha :)
 

InteGrand

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Quick question:

A cannon shot was fired at an elevation angle of 40. A second shot was fired at the same speed, but at an elevation angle of 60. Compared with the first shot, what would the second shot expected to have:

A. shorter range
B. longer range
C. shorter time of flight
D. longer time of flight

I picked A, because if the 2nd shot was fired at the same speed but a higher angle wouldn't Ux be smaller (and hence range is smaller)? The answer is apparently D (not from textbook, just a teacher's answer)

Cheers
 
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Jeff_

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Hey just a quick question about something I wrote in the exam:

Would it be correct if I wrote that when a magnet is dropped through a copper pipe, the eddy currents (... and here I state that its from Lenz's Law) will make the magnet fall slower and kinetic energy is converted into heat? The question was basically asking to compare the magnet falling in a copper pipe, to the induction cooktop. (So here it is somewhat similar that they both produce heat but in different ways).

Thanks :)
 

Bestintheworld

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^ not too sure.

Discuss the effects on the environment of the development of AC generators. (6 Marks)
 

leehuan

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^ not too sure.

Discuss the effects on the environment of the development of AC generators. (6 Marks)
Woah what... is this seriously a 6 marker?

I would've made it 6 if you also included social though..
 

Jeff_

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Hey just a quick question about something I wrote in the exam:

Would it be correct if I wrote that when a magnet is dropped through a copper pipe, the eddy currents (... and here I state that its from Lenz's Law) will make the magnet fall slower and kinetic energy is converted into heat? The question was basically asking to compare the magnet falling in a copper pipe, to the induction cooktop. (So here it is somewhat similar that they both produce heat but in different ways).
^ not too sure.
Just found this:

When a magnetic field moves through a conductor a current called an Eddy current is induced in the conductor due to the magnetic field’s movement. The flow of electrons in the conductor creates an opposing magnetic field to the magnet which results in damping of the magnet and causes heating inside of the conductor similar to heat buildup inside of power cords. The loss of energy used to heat up the conductor is equal to the loss of kinetic energy by the magnet.
(from http://thekidshouldseethis.com/post/75596084570)
 

leehuan

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That's just conservation of energy, I think

Honestly I reckon the main similarity is that in both cases on top of Faraday's and Lenz's law it's eddy currents being induced cause you obviously don't have a complete circuit

Clearly, the application of the induced currents differs, as one is used for heating whereas the other is used to slow down something. But because the question says to compare you would've had to include that as well because compare implies give similarities AND differences
 
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Jeff_

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That's just conservation of energy, I think

Honestly I reckon the main similarity is that in both cases on top of Faraday's and Lenz's law it's eddy currents being induced cause you obviously don't have a complete circuit

Clearly, the application of the induced currents differs, as one is used for heating whereas the other is used to slow down something. But because the question says to compare you would've had to include that as well because compare implies give similarities AND differences
Yeah that would make sense that the main similarity is the eddy currents. I guess I went onto the more specifics, thinking how heat is produced in the induction cooktop and therefore somehow the teacher might want us to talk about heat and eddy currents with magnet/copper pipe.
 
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