drav

drav ka koi nishchit aakaar naheen hota. drav jis paatr mein rakha jaata hai usi ka aakaar grahan kar leta hai.

prakruti mein sabhi raasaayanik padaarth saadhaaranat: thos, drav aur gas tatha plaajma - in chaar avasthaaon mein paae jaate hain. drav aur gas pravaahit ho sakte hain, kintu thos pravaahit naheen hota. lacheele thos padaarthon mein aayatan athva aakaar ko vikrut karne se pratibl utpann hota hai. alp vikrutiyon ke liye vikruti aur pratibl paraspar samaanupaati hote hain. is gun ke kaaran lacheele thos ek nishchit maan tak ke baahari balon ko sainbhaalane ki kshamata rakhate hain.

pravaah ka gun hone ke kaaran dravon aur gaison ko taral padaarth (fluid) kaha jaata hai. ye padaarth kartan (shear) balon ko sainbhaalane mein aksham hote hain aur gurutvaakarshan ke prabhaav ke kaaran pravaahit hokar jis baratan mein rakhe rahate hain, usi ka aakaar dhaaran kar lete hain. thos aur taral ka yaantrik bhed bahut spasht naheen hai. bahut se padaarth, visheshat: uchch koti ke bahulak (polymer) ke yaantrik gun, shyaan taral (viscous fluid) aur lacheele thos ke gunon ke madhyavarti hote hain.

pratyek padaarth ke liye ek aisa kraantik taap (critical temperature) paaya jaata hai, jisse adhik hone par padaarth keval taral avastha mein rah sakta hai. kraantik taap par padaarth ki drav aur gas avastha mein vishesh antar naheen rah jaata. isse neeche ke pratyek taap par drav ke saath usaka kuchh vaashp bhi upasthit rahata hai aur is vaashp ka kuchh nishchit dabaav bhi hota hai. is dabaav ko vaashp dabaav kehte hain. pratyek taap par vaashp dabaav ka adhiktam maan nishchit hota hai. is adhiktam dabaav ko sanprukt-vaashp-dabaav ke baraabar athva usase adhik ho, to drav sthaayi rahata hai. yadi oopari dabaav drav ke sanpruktavaashp-dabaav se kam ho, to drav asthaayi hota hai.

sanprukt-vaashp-dabaav taap ke badhne se badhta hai. jis taap par drav ka sanprukt-vaashp-dabaav baahari vaataavaran ke dabaav ke baraabar ho jaata hai, usapar drav bahut teji se vaashpit hone lagta hai. is taap ko drav ka kvathanaank (boiling point) kehte hain. yadi baahari dabaav sarvatha sthaayi ho to kvathanaank se neeche drav sthaayi rahata hai. kvathanaank par pahuainchane par yeh khaulane lagta hai. is dasha mein yeh taap ka shoshan karke drav avastha se gas avastha mein parivrtit hone lagta hai. kvathanaank par drav ke ikaai dravyamaan ko drav se poornat: gas mein parivrtit karne ke liye jitne kailori ooshma ki aavashyakta hoti hai, use drav ke vaashpeebhavan ki gupt ooshma kehte hain. vibhinn drav padaarthon ke liye iska maan bhinn hota hai.

ek niyat dabaav par thos aur drav donon roop saath saath ek nishchit taap par paae ja sakte hain. yeh taap drav ka himbindu ya thos ka dravanaank kahalaata hai. dravanaank par padaarth ke ikaai dravyamaan ko thos se poornat: drav mein parivrtit karne mein jitni ooshma ki aavashyakta hoti hai, use thos ke galan ki gupt ooshma kehte hain. akristali padaarthon ke liye koi niyat galanaank naheen paaya jaata. ve garam karne par dheere dheere mulaayam hote jaate hain aur fir drav avastha mein aa jaate hain. kaaainch tatha kaaainch jaise anya padaarth isi prakaar ka vyavahaar karte hain.

ek niyat taap aur niyat dabaav par pratyek dravya ki teenon avasthaaeain ek saath vidyamaan rah sakti hain. dabaav aur taap ke beech kheechein gaye aarekh (diagram) mein ye niyat taap aur dabaav ek bindu dvaara pradarshit kiye jaate hain. is bindu ko drav ka trik bindu (triple point) kehte hain. trik vindu ki apeksha nimn daabon par drav asthaayi rahata hai. yadi kisi thos ko trik vindu ki apeksha nimn dabaav par rakhakar garam kiya jaae to vah bina drav bane hi vaashp mein parivrtit ho jaata hai, arthaat oordhvapaatit (sublime) ho jaata hai.

drav ke mukt tal mein, jo us drav ke vaashp ya saamaanya vaayu ke sampark mein rahata hai, ek vishesh gun paaya jaata hai, jiske kaaran yeh tal tani hui maheen jhilli jaisa vyavahaar karta hai. is gun ko prushth tanaav (surface tension) kehte hain. prushth tanaav ke kaaran drav ke prushth ka kshetrafal yathaasanbhav nyoonatam hota hai. kisi diye aayatan ke liye sabse kam kshetrafal ek gole ka hota hai. at: aisi sthitiyon mein jab ki baahari bal naganya maane ja sakte hon drav ki booainde gol hoti hain. jab koi drav kisi thos, ya anya kisi amishraya drav, ke sampark mein aata hai to bhi sampark tal par tanaav utpann hota hai.

saadhaaranat: koi bhi padaarth keval ek hi prakaar ke drav roop mein praapt hota hai, kintu iske kuchh apavaad bhi milte hain, jaise heeliym gas ko dravit karke do prakaar ke heeliym drav praapt kiye ja sakte hain. usi prakaar paira-aijauksi-ainisol (Para-azoxy-anisole) prakaashat: vishmadaishik (anisotropic) drav ke roop mein, kristaleeya avastha mein tatha saamaanya drav ke roop mein bhi praapt ho sakta hai.

pratyek dravya ke anu ek doosare ko aakarshit kiye rahate hain. is aakarshan ko antaraanuk aakarshan kehte hain. isi ke kaaran kisi dravya ke anu ekatr rahate hain. dravya ke anuon par ek vikrshan bal bhi lagta rahata hai. yeh bal anuon ko ek doosare ke ati nikat aane se rokata hai. thos ke anuon ke beech ye bal prabal hote hain. dravon mein inke maan alp aur gaison mein lagbhag naganya hote hain.

kristaleeya thos ki laakshanik visheshata yeh hoti hai ki usamein nikat paraas (short range) aur door paraas (long range) mein bhi anuon ki ek suniyojit vyavastha bani hoti hai. kuchh anu aapas mein milkar chhote chhote gut bana lete hain. in guton ki aantarik rachana ek si hoti hai. inhein ekakakoshika (unit cell) kehte hain. yahi nikat paraas ki vyavastha kahalaati hai. door paraas ki vyavastha ka yeh arth hai ki kristaleeya thos ki ekakakoshikaaeain bhi vishesh dhang se vyavasthit rahati hain, arthaat ekakakoshika ki vyavastha manamaani (random) naheen varan aavarti (periodic) hoti hai. drav aur thos mein mukhya bhed yahi hai ki drav mein dooraparaas vyavastha bilkul naheen hoti hai. niktaparaas vyavastha kuchh had tak bani rah sakti hai, jisse drav mein bhi pratyek anu ke chaaron or sthit anuon ki sankhya baraabar hoti hai.

ex-kiran vivrtan (x-ray differaction) ke prayogon dvaara is prakaar ki nikat paraas vyavastha ki upasthiti vaigyaaniko dvaara pramaanit ki ja chuki hai. J.di. baranaal (J.D. Bernal) aur aar.H. faaular (R.H. Fowler) ne ex-kiran vivrtan ka adhyayan kiya hai aur usaki sankhya ka foorye (Fourier) vishleshan karke is tathya ko pratipaadit kiya hai.

drav ke kraantik vindu, shyaanata tatha anya gunon ki ganana ke liye bahut se saiddhaantik prayatn kiye gaye hain. pehle ke adhyayanon ke adhiktar lenaard jons vibhv (Lennard Jones poetntial) ka upayog kiya gaya hai. dravon ka vivr siddhaant (Hole Theory of Liquids) apekshaakrut naveen siddhaant hai.

bahut se drav vidyuchhuchaalak hain. inki chaalakata ka kaaran yeh hai ki inmein svatantr ilektraun paae jaate hain. drav lavanon ki vidyuchchaalakata unke aayaneekaran par nirbhar karti hai. anya drav do mukhya bhaagon mein baaainte ja sakte hain. jo drav vidyunmaya vastu ki or-aakarshit hote hain, unhein dhruveeya (polar) aur jo aakarshit naheen hote unhein adhruveeya (non-polar) kaha jaata hai. vaastavikta yeh hai ki dhruveeya dravon ke anu mein sthaayi roop se kuchh dvadhruiv-aaghoorn (dipole moments) hote hain, paratu adhruveeya dravon ke anuon mein aisa naheen hota. beinjeen adhruveeya drav hai. adhruveeya dravon ka paraavaidyutaank (dielectric constant) 1 aur 3 ke beech mein paaya jaata hai. inka drushya (visible) kshetreeya vartanaank inke radio aavrutteeya (radio frequency) paraavaidyutaank ke vargamool ke baraabar hota hai. dhruveeya dravon ke paraavaidyutaank adhruveeya dravon ke paraavaidyutaankon ki apeksha lagbhag 10 se 100 guna adhik hote hain, kintu inka vartanaank (refractive index) lagbhag utana hi hota hai. drav samaanyat: samadaishik (isotropic) hote hain.

dravon ke varnakram inheen padaarthon ke gaiseeya aanavik varnakramon se bahut kuchh milte julate hain. par dravon ke raman (Raman) aur avarakt (infra-red) varnakram sangat gaiseeya varnakram se kuchh bhinn hote hain.