Biology; Chemistry; Physics: Post your doubts here!

[kitecrystal]

relationship b/w resistance and current ??

inverse propotion as V=IR,hence I=V\R.

 

[convent2012]

need help in 9,26,33,37,40.

9 A because as two spring are hung with same load , extension wil be half .

 

[kitecrystal]

9 A because as two spring are hung with same load , extension wil be half .

thanku.

 

[asd]

describe and explain circuits operating as light-sensitive switches and temperature operated alarms(using a reed relay)
copy from syllabus...

http://www.xtremepapers.com/papers/...onal O Level/Physics (5054)/5054_s09_qp_2.pdf
Look at the question no 7 part c.
It is normally used along with a coil. Now, thermistor attached to the second circuit actually reduces the resistance in the circuit when there is a high temperature (say, a fire in the building) The coil produces a magnetic field and the contacts are magnetised. Apply the Right-hand rule to see where the N-pole forms. The contact on the left forms a N-pole on it's left end, and therefore a S-pole on it's right end. Similarly, from Right-hand rule you know that N-pole forms on the left, so there will be a S-pole on the right end of the right contact, and therefore a N-pole on its left end. The contacts attract each other and circuit closes. The alarm is switched on.

Now, for a light sensitive circuit use an LDR in place of thermistor!

 

[Dukeofwin]

need help in 9,26,33,37,40.

9 is A because the increase in load is shared between two springs.
26 is D beacuse iron magnetizes and demagenetises quickly
33 is C use L.H.R
37 is B because when resistence increase less current flows thus the capacitor discharges very slowly
40 is A because Alpha Particles go straight pass the foil!

 

[a.abid]

http://www.xtremepapers.com/papers/CIE/Cambridge International O Level/Physics (5054)/5054_s09_qp_2.pdf
Look at the question no 7 part c.
It is normally used along with a coil. Now, thermistor attached to the second circuit actually reduces the resistance in the circuit when there is a high temperature (say, a fire in the building) The coil produces a magnetic field and the contacts are magnetised. Apply the Right-hand rule to see where the N-pole forms. The contact on the left forms a N-pole on it's left end, and therefore a S-pole on it's right end. Similarly, from Right-hand rule you know that N-pole forms on the left, so there will be a S-pole on the right end of the right contact, and therefore a N-pole on its left end. The contacts attract each other and circuit closes. The alarm is switched on.

Now, for a light sensitive circuit use an LDR in place of thermistor!

That is correct

 

[snoonono]

guys go here for physics revision http://www.xtremepapers.com/community/threads/physics-o-levels-post-doubts-plz.16372/#post-279765

 

[bogus]

lol...Well split rings help in reversing the current, while slip rings help the generator to connect to the external environment,AC generator does not need any split rings cuz the current is already reversing,so it wont work...Thats wat I think :/

will stop in vetical position

 

[luckywang]

http://www.xtremepapers.com/papers/CIE/Cambridge International O Level/Physics (5054)/5054_s09_qp_2.pdf
Look at the question no 7 part c.
It is normally used along with a coil. Now, thermistor attached to the second circuit actually reduces the resistance in the circuit when there is a high temperature (say, a fire in the building) The coil produces a magnetic field and the contacts are magnetised. Apply the Right-hand rule to see where the N-pole forms. The contact on the left forms a N-pole on it's left end, and therefore a S-pole on it's right end. Similarly, from Right-hand rule you know that N-pole forms on the left, so there will be a S-pole on the right end of the right contact, and therefore a N-pole on its left end. The contacts attract each other and circuit closes. The alarm is switched on.

Now, for a light sensitive circuit use an LDR in place of thermistor!

thanks! it is very helpful!

 

[syed1995]

Could someone give me any idea/notes on how the electrons/beta particles/alpha particles deflect in an magnetic field which is into the page or out of the page??

 

[luckywang]

http://www.xtremepapers.com/papers/CIE/Cambridge International O Level/Physics (5054)/5054_s09_qp_2.pdf

but how about q7 part(a)? is the whole left iron bar become north pole or one end is north while the other end is south?

 

[luckywang]

Could someone give me any idea/notes on how the electrons/beta particles/alpha particles deflect in an magnetic field which is into the page or out of the page??

use fleming left hand rule!

 

[bogus]

transistor notes any one?

 

[asd]

Left hand rule. If the question states that magnetic field is out of the page/into the page, you'll have to give you answer with respect to top/bottom of the page.
For protons (carrying positive charge) the direction of the current will be the same as shown. For eg: Field is into the page (x)(x)(x)(x)(x), and the alpha particles/protons are released from left to right, from flehming's left hand rule, they will divert to the top of the page.
Your middle finger ( ) to the right ----> for alpha particles, and your first finger towards the floor (for field which is into the page). You will see your thumb pointing forwards, which depicts they will divert to the top of the page.
For electrons/beta-particles, point your middle finger to the opposite side of the direction shown (for the particles), because the electrons carry -ve charge (opposite to that of protons)

Could someone give me any idea/notes on how the electrons/beta particles/alpha particles deflect in an magnetic field which is into the page or out of the page??

 

[syed1995]

use fleming left hand rule!

how? where to point when it is inside the page and outside the page?

 

[syed1995]

For protons (carrying positive charge) the direction of the current will be the same as shown. For eg: Field is into the page (x)(x)(x)(x)(x), and the alpha particles/protons are released from left to right, from flehming's left hand rule, they will divert to the top of the page.
Your middle finger ( ) to the right ----> for alpha particles, and your first finger towards the floor (for field which is into the page). You will see your thumb pointing forwards, which depicts they will divert to the top of the page.

the finger's pointing towards the bottom of the page (Towards My Face to explain it.) in this instance .. is that right? :s

 

[luckywang]

how? where to point when it is inside the page and outside the page?

just point toward the page or opposite of the page....

 

[luckywang]

transistor only included the npn transistor?

 

[asd]

the finger's pointing towards the bottom of the page (Towards My Face to explain it.) in this instance .. is that right? :s

If your face is in line with your finger then yes. Bottom of the page is simply BACKWARDS.

 

[asd]

but how about q7 part(a)? is the whole left iron bar become north pole or one end is north while the other end is south?

but how about q7 part(a)? is the whole left iron bar become north pole or one end is north while the other end is south?

For the left iron bar: One end is north (which points towards the South pole of the magnet) and the other is S-pole (that points towards the North pole of the magnet)
For the right iron bar: Conclude yourself, want to see if you understand.
Hint: Induced magnetism always induce an opposite pole on the object to attract it!