After getting everything wrong last time, Bob now asks for help when he\'s confu
ID: 1568834 • Letter: A
Question
After getting everything wrong last time, Bob now asks for help when he's confused. Help him become less confused by answering his questions below. Note: just because it's Bob saying these things doesn't mean that they're easy to answer. Think through each of them carefully! d) "Speaking of capacitors, since C = Q / V, that means if Q = 0, then C = 0 too, right? e) "Why are there at least two prongs on every electrical plug? If power is traveling in one direction (from the wall to the appliance), why can't there be just one wire carrying it? And don't just say 'because circuits need to be closed' - after all, current can flow through a capacitor, and that's an open circuit. f) "I have a great idea that should make me filthy rich. I'm going to build a generator with a huge number of loops and an enormous magnetic field, but also with very low friction materials. That way, the opposing force against the spinning loops will be negligible. Therefore due to inertia, the loops will spin forever, with only very minimal input power to overcome the tiny amount of friction. In other words, I have found a loophole in conservation of energy: more electric power will be output than the mechanical power that was input. Who can stop me?!"Explanation / Answer
d)
Kinetic energy is given by KE = (1/2)mv2, Now, if KE = 0 would that mean m = 0?? No.
Just like that when Q = 0, we get CV = 0, this simply indicates that the product of two quantities, C and V is zero. So, there can be 3 cases - either C is zero, or V is zero, or both C and V are zero.
But, C is the intrinsic property of an object of praticular configuration. It depends only on the diemnsions of the object consedred as capacitor. Charge Q and voltage V adjust themsleves to keep the C constant.
So, Q = CV = 0 would just make V = 0, and won't affect the capacitance at all.
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e)
"Current can flow through a capacitor, and that's and open circuit." :- It's just wrong.. It's an open circuit only when the capacitor is fully charged and at that time the current stops and does not flow...
During its charging, the circuit is certainly not open and current flows. So, "current flow through a cpacitor" and "open circuit", both do not happen at same time........
So, the premise Bob used to discard the "circuit needs to be closed" theory is baseless.
You do need a closed circuit for the current to flow....
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f)
Forget even the tiny friction, even if Bob removes all the friction by some magic, he is not going to get what he wants.
Lenz's law will make sure of that.
When the coil moves through a magnetic field and the flux through the coil is increasing, the induced current in the coilwould be in such a direction so as to oppose the original field which produced it. To overcome this opposition you would have to do work against it to keep the coil moving and keep the current flowing.
Similarly, when the coil moves through a magnetic field and the flux through the coil is decreasin, the induced current in the coil would be in such a direction so as to oppose the original field which produced it. To overcome this opposition you would have to do work again.
So, in any case, you have to do work to move the coil through the field to get the current even without frition. Friction is just an additional opposition you have to overcome.
It's not so easy to be filthy rich after all!!!!!!!!!!
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This concludes the answers. Check the answer and let me know if it's correct. If you need any more clarification or correction, feel free to ask.....
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