A2 Physics | Post your doubts here

[smzimran]

Hey folks,
please explain me this question! Q6 part b1 and and part c of MAY/JUNE2009, Q9 of MAY/JUNE 2009, and Q10 c2( my answer is coming as 10V but in M.S it is 9.0V)
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s09_qp_4.pdf

Q6(b)(ii):
F = BIL
mg = BIL
Substitute values
(2.3 × 10^-3) (9.8) = B × (2.6) (4.4 × 10^-2)
B = 0.20 T

Q6(c):
Peak value, I0 = 2.3 × √2 = 3.25 A
The a.c current has one peak at positive value and the other peak at negative value so,
Variation at positive peak = 3.25 g
Variation at negative peak = - 3.25 g
The total variation is
= (3.25) - (-3.25)
= 6.5 g

Q10(c)(ii):
Vin = +0.4 V
Vout = Gain * Vin
Vout = 25 * (+0.4)
Vout = 10 V

But this output is more than the supply of the op-amp, therefore the amplifier saturates and the output is equal to the supply voltage!
So,
Vout = 9 V

 

[smzimran]

people wth is all this derivation of weird equations in the ideal gases chapter? do I neeed to know them?

Yes, you need to!

 

[optimistic]

Q6(b)(ii):
F = BIL
mg = BIL
Substitute values
(2.3 × 10^-3) (9.8) = B × (2.6) (4.4 × 10^-2)
B = 0.20 T

Q6(c):
Peak value, I0 = 2.3 × √2 = 3.25 A
The a.c current has one peak at positive value and the other peak at negative value so,
Variation at positive peak = 3.25 g
Variation at negative peak = - 3.25 g
The total variation is
= (3.25) - (-3.25)
= 6.5 g

Q10(c)(ii):
Vin = +0.4 V
Vout = Gain * Vin
Vout = 25 * (+0.4)
Vout = 10 V

But this output is more than the supply of the op-amp, therefore the amplifier saturates and the output is equal to the supply voltage!
So,
Vout = 9 V

Can you explain Q6b 1 too?

 

[smzimran]

Can you explain Q6b 1 too?

Use fleming's left hand rule,
current in from X to Y (second finger)
force is upwards (thumb)
the direction where your forefinger points is the direction of the field, check it

 

[angelicsuccubus]

does anyone have notes on the direct sensing, medical imaging and communication systems chapters? ... I'm running low on energy and I can't deal with readin this shit any longer!

 

[smzimran]

does anyone have notes on the direct sensing, medical imaging and communication systems chapters? ... I'm running low on energy and I can't deal with readin this shit any longer!

Have you seen Chris Mee book ?

 

[optimistic]

Use fleming's left hand rule,
current in from X to Y (second finger)
force is downwards (thumb)
the direction where your forefinger points is the direction of the field, check it

I understand that but i don't get why force on wire is upwards? in the marking scheme they are saying pole P is North

 

[smzimran]

I understand that but i don't get why force on wire is upwards? in the marking scheme they are saying pole P is North

Because magnetic force balances weight

 

[angelicsuccubus]

Have you seen Chris Mee book ?

nope..

 

[angelicsuccubus]

I understand that but i don't get why force on wire is upwards? in the marking scheme they are saying pole P is North

I have no idea what you guys are talking about but reading the two comments reminded me of Lenz's law... lenz's law always makes the force the other way round.

 

[smzimran]

I have no idea what you guys are talking about but reading the two comments reminded me of Lenz's law... lenz's law always makes the force the other way round.

This is not electromagnetic indution!
Lenz Law is used when an e.m.f is induced by a moving coil or magnet!
This is just electromagnetism

 

[smzimran]

nope..

See it, its given somewhat better in that!

 

[angelicsuccubus]

This is not electromagnetic indution!
Lenz Law is used when an e.m.f is induced by a moving coil or magnet!
This is just electromagnetism

okay okay sorry!

 

[angelicsuccubus]

See it, its given somewhat better in that!

and where am I supposed to find that book at this ungodly hour?

 

[smzimran]

and where am I supposed to find that book at this ungodly hour?

Can't help with that!

 

[optimistic]

Because magnetic force balances weight[/quotb
but si

Because magnetic force balances weight

Thanks!

 

[optimistic]

please explain me MAY/JUNE 2009 Q 2 part a
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s09_qp_4.pdf

 

[angelicsuccubus]

please explain me MAY/JUNE 2009 Q 2 part a
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s09_qp_4.pdf

half life is the time taken for half the atoms to decay, in this case by alpha decay. Half life pltted against time has an exponentioal slope and so seen as constant, which means the time taken for alpha decay is constant.

 

[optimistic]

half life is the time taken for half the atoms to decay, in this case by alpha decay. Half life pltted against time has an exponentioal slope and so seen as constant, which means the time taken for alpha decay is constant.

but why have they taken 40 days as half life?

 

[angelicsuccubus]

but why have they taken 40 days as half life?

because that's the only time they've given? I donno.. maybe cause they implied that the alpha decay was only for 40 days?... maybe they are just bad at wording the question. It doesn't matter.. its the only time given so it has to be the half life..