Biology; Chemistry; Physics: Post your doubts here!

[Anon]

You are one "awesome" teacher...
Can you grace the Add.Maths thread too?

I have a query there...

EDIT: just realised Add.Math is not your subject... ah..bad luck..

 

[SalmanPakRocks]

Oye buddhu, when you provide a separate (easier) pathway for current, the second 3 ohms resistor doesn't share the circuit anymore.
(Even if it does, that's not part of your syllabus)

Oh yeah, sorry but my teacher is too good to teach me so I learn mostly from notes or Youtube.
Thank u for explaning!

 

[Anon]

A question of Physics:

16 What is caused by the thermal expansion of a substance when heated?

A - a decrease in the resistance of a tungsten-filament lamp when switched on
B - a rise in the pressure of the gas trapped in a gas cylinder placed in hot water
C - the blowing of the fuse in a circuit when the current becomes too large
D - the upward movement of the air above a Bunsen burner when it is lit

The thing is, I find another option, other then an answer, equally good enough to qualify as one..

 

[Anon]

There was an explanation to this answer in Error Report..
According to it, majority got it wrong..

So no need to brainstorm over it,

 

[abcde]

I believe the answer is D. Which is the correct one and your secondary choice?

 

[abcde]

There was an explanation to this answer in Error Report..
According to it, majority got it wrong..

So no need to brainstorm over it,

One must read and examine the mark scheme and er before posting a question. My opinion. Anyway, Kudos!

 

[Anon]

Yeah answer is D.

But B seems pretty plausible as well..

But er said, that gas have not actually expanaded in the container, so there is no thermal expansion..

 

[Anon]

Your'e right. I had read the ms, but not er...

Alert: Another question is on its way...

 

[Anon]

Here is the question:

I was able to answer it, but it was due to a very logical reason, and not the understanding of the concept..
Can anyone explain voltage time graph, compared to rotation of the coil, in light of this question.

 

[abcde]

Obviously! The word 'trapped' is an indication 'B' is incorrect.
When the coil is in the horizontal position, there is maximum cutting of magnetic field lines, thereby inducing maximum voltage, leading to a point that is either A or C on the graph. The vertical position of the coil corresponds to 'B' as there is no cutting of magnetic field lines and hence no induced emf (=> zero voltage output). You can very well imagine that being in the vertical position, the magnetic lines of force would pass through the 'hollow portion' of the coil.

 

[Anon]

Thanks a dozen abcde..
I would remember the hollow part thing...

Actually with Physics Exam tomorrow, Speed is the Essence..
Thanks again.

 

[Nibz]

Answer is B.

Here's the thing:
When the coil is horizontal, the coil 'CUTS' the magnetic lines with greatest rate, i.e, magnetic flux is greatest. (Max or min point on graph)
When the coil is vertical, the coil 'CUTS' the magnetic lines with least rate, i.e, magnetic flux is smallest => Voltage = 0 graph at x-axis.

 

[Nibz]

Sorry for any confusion. I had no idea someone already posted the answer. Net's driving me crazy!

 

[Anon]

Thank you tooo Nibzy..

Will remember that....

 

[scouserlfc]

this image will help u get it !

 

[Anon]

Sorry for any confusion. I had no idea someone already posted the answer. Net's driving me crazy!

Na, it just clarified the original.

Thanks again

 

[Nibz]

Anytime.

 

[Anon]

Thanks scouserlfc...
btw, where di you got the pic from?

ALso, what determines, that voltage produnced is negative or positive..

 

[abcde]

Someone? :O
You're welcome!

 

[scouserlfc]

u see that the currents switch like if u take a wire ABCD the current in wire AB points in one direction before half Revolution then it points in the other