CURRENT DOUBTSS.....:):)

well now the above law shows whenever there will be a changing electric field there will be magnetic induction or in better words when there is a changing electric flux in free space, a magnetic field is created(relate with electromagnetic induction they are similar)

so both rotation and revolution HAS to create magnetic field!!

Now, clockwise spins have a magnetic effect and an anticlockwise spin has exactly same magnetic effect but in just opposite directions...(Electrons are subject to Pauli's Exclusion Prnciple and have spin ±12 and are fermion particles)

also accordind to hund's rule of maximum multiplicity, the electrons first fill in ALL the degenerate orbitals with SAME spin and after all the degenerate orbitals are filled that the opposite spin filling starts...

again...those which have unpaired electrons are called paramagnetic and those having all paired electrons are called diamagnetic...paramagnetic substances having unpaired spins are capable of orienting themselves with any externally applied magnetic field...opposite is the case with diamagnetic...

Iron has a high number of unpaired electrons...i.e. FOUR and hence forms a HIGHLY para-magnetic group called FERROmagnetic...

the best ferromagnetic substance by my logic would be Chromium(3d⁵4s¹) with SIX unpaired electrons(i am excluding f block elements)
but since iron is highly abundant and has fairly large ferromagnetic nature, it and its alloys are widely used for making magnets!!!

a magnet not only attracts iron, but it also attracts all other ferromagnetic substances and paramagnetic substances...

in this regard it is to be mentioned that para magnetic substances and ferromagnetic compounds can be ROUGHLY distinguished by saying paramagnetic substances contain 1-2 unpaired elecs and ferro has 4-5-6 and so on!!

Magnets are MADE of iron coz as earlier stated for abundance and for 2 other properties that iron has higher permeability and lower retentivity(iron is used to make most temporary magnets while steel with lower permeability and higher retentivity are mostly used to make permanent magnets!!)

# 14 is now open as a googly from ATGS 16!!

http://www.targetiit.com/iit-jee-forum/posts/googly-from-atgs-16-17237.html

lets see whats the general idea about it!!

ek secret batata hoon:: the question is a very silly one and so is the answer!!

@Sanchit : i hope reading HC V will help u in ur doubts!

yeah J is the current density

will write at night...bye!

Returning to the ORIGINAL question of the THREAD!!

look u can do 2 approaches to the problem!!

FIRST!!!

by symmetry u try to find out points with same potential !!

now we tingle our bacic concept to know that points of same potential THOUGH CONNECTED will never have any current in the bridge between them...

also we know that 2 points which are NOT connected will have no current between them...

so in symmetry what we basically do is try and find out all the equipotential points...now if the points are connected, we can detatch them(in any case no current flows through them) or if the points are NOT connected, we SORT them(in any case there is going to be no current!!!)

For simplest example, we consider a WHEATSTONE BRIDGE!!

The 2 bridged points whether sorted or detatched will always give the same equivalent resistance(try out yourself!!)

For a and b refer to H C Verma chapter: Permanent magnets...

there the thing is explained better that my patience would ever permit me to write!! :)

for h)

come-on man! now do not ask this question....

well i ask u a similar question...if u know the answer of the question I ask then u ll be able to answer ur doubt number h) urself!!

the question is...

In electron's frame of reference, attractive electrostatic force is balanced by centrifugal force [don't chuckle to read that word as many including me often do ;)] and thus doesnot move! (remember we are in electron's reference frame!)

NOW we change reference frame to the nucleus, the only force acting on it is the force of electrostatic attraction due to eletrons and STILL the nucleus doesnot accelerate towards the electrons!! the question is WHY??? :P

i THINK that c.d.e.f.g are answered!!

well, a changing electric field or a flowing charge (which causes change in electric field) induces a magnetic field...

the second part is very obvious as given by ampere's circuital law or biot-savart's law...

but consider a case...

When an uncharged capacitor is connected across a battery, there flows a current and supplies charge to one plate of capacitor...also the other connecting wire, conducts current and takes away charge from the other plate of capacitor...

here it must be noted that no charge flows between the two capacitor plates but by observation, we find a magnetic field being created in that region...

this observation was historically used by maxwell to redefing ampere's circuital law!!

the circuital law stated,

\oint_{c}^{.}{B.dl}=\mu_o \int\!\!\!\!\!\int_{A}^{.}{J.dS}=\mu _oi

Maxwell restated it as,

\oint_{c}^{.}{B.dl}=\mu_o \int\!\!\!\!\! \int_{A}^{.}{(J+\epsilon _o\frac{\partial E}{\partial t}).dS}

where, \int\!\!\!\!\! \int_{A}^{.}f(x)dx mean surface integral(do not get confused by double integral sign)