IIT JEE , AIEEE Forum - Physics , Mechanics - A metal sheet with a hole is heated uniformly.

ADPDAVCTC

HOW THE HOLE GETS LARGER? THE SOLUTION READS :comparatively,the expansion of the hole is more than its contraction . WHY the expansion is only outwards,why it cannot be inwards to make the hole smaller?

supreet159

look at da edge of the hole...now due to uniform heatin the edje expand as the metal expands due to xpansion ....simple ...got it

anchitsaini

Heating means giving energy that is the electrons will have more kinetic energy and would try to separate as much as possible from each other , hence the expansion occurs and not the contraction

ADPDAVCTC

IF THE EDGE EXPANDS ,THEN THE HOLE WILL BECOME SMALLER
I think u want 2 say if the outer edge will expand outwards,then the inner edge will also expand outwards only by that much.
but how is that possible, there will be no relative apparent expansion.

ADPDAVCTC

i just don't want about any K.E OR CONTRACTION . I JUST WANT
THAT WHY THE EXPANSION IS OUTWARDS NOT INWARDS?

sagarvaze

simple consider the inner hole now if it expands inwards then circumference decreases which means distance between adjacent molecules on heating decreases which is not possible

(**321**)

The expansion, for me must be both sides...inwards as well as outwards...

sagarvaze

see if hole expands inwards distance between adjacent point has decreased which is not possible

v.sabarish

Forget everything else, the answer is very simple and straight
When you heat it, the disc expands, but the relative dimensions of the hole and the disc remain unaltered. Put in better words, the ring after heating would just look like a magnified image of the original one
The disc, as well as the hole, is magnified
I guess you get my poing

ADPDAVCTC

answering 2 sagarvaze if the inner hole expands inwards,then how can u be so sure that the circumference decreases,it can increase expanding outward as well therby increasing the gap between adjacent molecules which is possible.
I PARTIALLY AGREE WITH V.SABARISH.
FINALLY PLEASE TELL ME WHETHER THIS STATEMENT IS CORRECT:the circular hole becomes smaller(shrinks)& the circumference becomes larger.
I want 2 knw whether expansion is unidirectional or polydirectional?
eg :if a 1m^3 cubical body is heated uniformly & suppose it expands by 6m, then expansion is 1m on all the6 sides or 3m & 3m in 2 opp.sides or 2m in one side & 4m in another side or 1m in one side& 5m on another or 2,2,2 or 3,2,1 or..........etc.

ADPDAVCTC

yes thank u very much sagarvaze 4 ur diagram. now, i understand everything....the hole can never become smaller.....as the k.e increases,the molecules will try to b far apart which is not possible
between 2 adjacent molecules placed radially or along the circumference of small concentric circles near the hole.

v.sabarish

About the statement you've made... there isn't much clarity...
"the circular hole becomes smaller(shrinks)& the circumference becomes larger."
smaller w.r.t what?
smaller w.r.t its previous size, or its size relative to the disc??
If it's w.r.t its previous size, it may expand or shrink, depending on heating or cooling ... but relative to the disc, it's size remains unaltered

ADPDAVCTC

thanks sabarish for ur idea of w.r.t ..... i was asking w.r.t disc.
RELATIVE 2 DISC ,ITS SIZE REMAINS UNALTERED, do u want 2 say that as much the inner hole expands outwards ,the outer circumference will expand outwards by that much only.Then there will be no relative expansion w.r.t. disc.

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Heating means giving energy that is the electrons will have more kinetic energy and would try to separate as much as possible from each other , hence the expansion occurs and not the contraction