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# AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread] watch

1. (Original post by ajonesyw)
Attachment 425287

I dont understand why induced EMF is at greatest when the rotation at B is parralel to the field lines? Because this means its not cutting any at this point?

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Emf is proportional to the change in flux and when the cool is parallel a change in flux has taken place from BAN when the coil was perpendicular to 0 when it is parallel. This change causes an emf to be induced.
2. (Original post by ajonesyw)
Can someone explain why potential is negative? and how many and which satellite equations do we need to know? cheeeeeeerss
potential isn't negative is a scalar quantity
3. Today's the day guys. Just wanted to say thank you for this thread it's been a life saver! I hope it goes well for you all - you all deserve the grades you want. Good luck!

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4. (Original post by _Caz_)
Today's the day guys. Just wanted to say thank you for this thread it's been a life saver! I hope it goes well for you all - you all deserve the grades you want. Good luck!

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Good luck to you too! I remember when this thread was in its infancy!

Hope it goes well

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5. (Original post by SA043)
potential isn't negative is a scalar quantity
It is negative actually, because to accelerate something towards Earth (attraction), we get work out of the system rather than having to put work into a system
6. Can I ask, if momentum is a vector, how come when it rebounds momentum becomes 2mv?

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7. An elastic collision will cause a colliding object to change from momentum = mv to momentum = -mv, since velocity is reversing and all is conserved. It doesn't change to 2mv, but the total overall momentum change over the collision is 2mv
8. (Original post by NotLuis)
An elastic collision will cause a colliding object to change from momentum = mv to momentum = -mv, since velocity is reversing and all is conserved. It doesn't change to 2mv, but the total overall momentum change over the collision is 2mv
Cheers! But how come the velocities don't cancel?

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9. Good luck!
10. Good luck everyone!!
11. (Original post by xela238)
Cheers! But how come the velocities don't cancel?

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mv - - mv = 2mv
12. (Original post by QueNNch)
mv - - mv = 2mv
Ahhhh ok thanks!!! Good luck!

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13. (Original post by CD223)
Good luck to you too! I remember when this thread was in its infancy!

Hope it goes well

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Yeah great thread, hope everyone gets what they need!

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14. do we always take the direction positive which the momentum acts ? (i.e. he football ques with the impulse graph)
15. Does a step down transformer have less turns on the secondary than the primary?

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16. (Original post by huniibehi)
Does a step down transformer have less turns on the secondary than the primary?

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Step down has more on the primary less on the secondary

Visa versa for step up

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17. (Original post by huniibehi)
Does a step down transformer have less turns on the secondary than the primary?

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Yep number of turns is proportional to velocity

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18. I just remember it as step up - voltage up, turns up

Step down- Voltage down, number of turns down.
19. (Original post by _Caz_)
Yep number of turns is proportional to edit voltage I MEAN VOLTAGE OMG WHAT US WRING WITH ME

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20. I'm going now before i cause any more confusion. But yeah number of turns is proportional to voltage!

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