12.14 Which magnet will hit the ground first?
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- čas přidán 28. 06. 2024
- This is an example of Faraday's and Lenz's law applied. As the magnet moves through the coil there is an increase and decrease in magnetic flux so there will be emf induced. The direction of emf will also change. There will be a repulsive and attractive magnetic force acting on the magnet and coil which is trying to oppose the change in flux. Overall effect is to reduce the accleration of the magnet. Finally we can explain all of this using a emf induced against time graph.
Topics for A-level Physics: AQA Paper 2, OCR paper 2, Edexcel Paper 1 and NCERT Class 12
00:00 - Intro
00:20 - Explanation entering
01:15 - Explanation leaving
02:06 - Coil with gap
02:28 - Emf-time graph
05:13 - Questions
05:23 - Answers
#A_level #physics #magnetic_field
Hello, i have a question. Say we have 3 coils, coil 1 has the greatest resistivity, then coil 2 and finally coil 3 with the least resistivity. If Magnet P fell through coil 1, Magnet Q through coil 2 and Magnet Y through coil 3, which magnet would fall to the ground in the shortest time and why?
Magnets are identical and when they fall through coils there is the same change of flux and same emf induced. The coil wilth lowest resistivity will have largest current so will produce biggest magnetic field to oppose the change in flux. It will repel (at first) and then attract (when coil has gone through) such that magnet Y hits the ground last. Magnet P first and magnet Q in between.
Hope that helps.
@@MrNagaPhysics Thank you!
Why is the emf time graphs gradient not reversed due to Lens’ law?
The gradient of the emf-time graph doesn't need to follow any law.
(The area does need to add up to zero, because it is the flux change)
Lenz's law tell us the gradient of flux-time gives the value of emf at any point in time.
@@MrNagaPhysics I understand that but in your other videos and in the equation for Lenz’s law there’s a negative sign so surely the negative of the flux time graph gradient give the emf at a given time not just the gradient of the flux time graph itself
@@davidoloughlin7612 Oh i see what you're saying.
What's important is that the direction changes as the flux increases and then decreases.
If i had switched the terminals of the voltmeter it would read negative then positive.
So it can be drawn either way, you should get the marks either way. Including in my old videos. I emphasised it there just to ensure students understood the negative is there.