OHM'S LAW
Ohm's law states that if all physical condtions remains same , then potential across the ends of conductor is directly proportional to the current flowing through it.
V ∝ I
V/I = constant
To remove the sign of proportionality we need a constant which is resistance and is represented by R
V = IR
(Ohm's law ne sirf ye kaha tha ki agar physical conditions yani ki temperature, pressureetc same ho to current potential ke directly proportional hoga. Ab dekho isse ek hi equation mili hai to proportionality ke sign ko hatana ke liye ek constant ki jarorat padegi jo yaha pr resistancehai. Jinhe nhi pata vo jaan lo ki jab bhi proportionality ka sign hataya jata hai to vaha pr ek constant jaroor aata hai. Shyad nineth me gravitation mai G ke bare mai yaad ho vo bhi ek constant hai. Ab ye resistamce kya hai ye apne aap mai hi ek bada topic hai is liye me alag se cover karunga. Baki voltage or current ka graph ek straight line hoga agar temperature same ho to.)
RESISTANCE
Resistance is the property of a conductor to resist the flow of charges.
Resistance is the obstruction in the path of flow of current.
S.I Unit of resistance is ohm. It is represented by the Greek letter Ω.
By ohms law, we can say that
R = V/I
Where R is resistance
V is potential difference across the ends of conductor
I is current
If the potential difference across the end of conductor is 1volt and the current flowing through it is 1 ampere then we can say that the resistance is 1 ohm
From the equation we can say that resistance is inversely proportional to current. If the current is doubled then resistance get halved and vice versa.
A device which is used to provide resistance is called resistor. And the device which is used to provide variable resistance is called rheostat or variable resistance.
( Vo property jo current ke flow ko rokne ki koshish kre use resistance kehte hai. Ab dekho current tab banta hai jab charged particles yani ki electrons flow hote hai. Vaise ye baat har kisi ke samajh nhi aaegi na hi tumhare syllabus me hai pr jise jan na hai ki resistance ka reason kya hai vo yeh samajh lo ki jab electrons flow hote hai tab vo atoms se takrate hai kyoki atoms se electrons nikal jane ke baad ab usme postive charge as compared to negative charge jyada ho jata hai. Ab jaise hi positively charged atom ( jise kernel bhi bolte hai) ke aas paas se koi electrons flow krta hua jata hai to ye kernel uspr attraction forces lagwakar use collide krwate hai apne aap se jisse uske path me ek obstruction create hoti hai. Bas yehi obstruction to resistance ye. Ab ye to clear hai ki ye har material ke liye alag alag hogi. Ab jo bataunga vo aapke syllabus mai hai to use dhyan se samjh lena. Resistance ki S.I unit ohm hai jo ki obviously George Simon Ohm jinhone Ohm's law diya hai unke naam pr hai. Ab ohms law se resistance ki equation bhi aa gayi ki resistance current ke inversely proportional hota hai. Yani agar aap current ko decrease kroge to resistance increase hogi aur agar aap resistance ko decrease kroge to current increase hoga. Ab ye dekho ki jab current lagta hai to hum ye kyo nhi bolte ki volt lag gaya. Kyoki volt sirf ek difference hai jo current ke flow ka karan hai baki jo hai current hai. Agar aap 11 hazar voltage ki taar ko hath lagaoge to aapko current marega voltage nhi.)
FACTORS ON WHICH RESISTANCE OF A CONDUCTOR DEPENDS
Resistance of a conductor
> depends on the length of conductor
>depends on the cross section area of conductor
HOW RESISTANCE DEPENDS ON LENGTH
Resistance is directly proportional to the length of conductor. Means increasing the length of conductor means increasing its resistance.
But resistance is inversely proportional to the area of cross section of conductor.
From the above definitions, we have
Where R = resistance
L= Length of conductor
A= Area of cross section
Where ρ (rho) is the constant of proportionality and is called electrical resistivity.
Resistivity is the property of material and is independent of length and area of conductor. The S.I Unit of resistivity is Ωm (ohm metre).
It is a characteristic property of material and vary from material to material. For example metals have low resistivity as compared to alloys.
Both the resistance and resistivity of a material vary with temperature.
Alloys do not burn readily at high temperature and have high resistivity as compared to their constituent metals thats why they are used in heating devices like iron, toaster, heating coils etc.
Tungsten is used as the filament of bulb 💡.
(To resistance do chijo par depend krti hai ek to hai length of conductor yani ki kisi bhi conductor ki lambai kitni hai aur dusri chiz hai area of cross section. Ab length jitni jyada hogi utna jyada electrons ke bich me collision hoga aur utni resistance badhegi aur agar area jyada hoga to electrons easily flow ho payenge aur resistance kam ho jayega. Yaad rakhna ki length ke sath questions mai tumhe diameter aur radius diya hoga to pehle uska area nikal lena kahi sidha isi ki value put kr do. Haan to mai yeh keh rha tha ki resistance length se directly proportional hai yani ki agar length double hogi to resistance bhi double hogi aur agar length half ho gyi to resistance bhi half ho jayegi. Aur area se resistance inversely proportional hoti hai yani ki area half kr doge to resistance double ho jayegi. Ab is se do equations nikalti hai unko combine krke ye jo uper likhi hai r∝l/a haan ye wali equation bni hai. Ab proportionality ke sign ko remove krne ke liye ek constant ka use krenge jise resistivity kehte hai. Yaar dekho naam se hi lag rha ki resistance ki judwa behan hai. Resistivity ek specific resistance hoti hai kisi material ki jo ki unit standard dimensions mai nikali jati hai. Nhi samjh aaya to ye samajh lo ki ye material ki property hoti hai. Yaar just imagine ki agar resistivityka concept na ho to hame pata hi nhi chalega ki transmission wire me aluminium aur home appliances me copper wire kyo lagate hai. Agar resistivity na to same size ki kisi bhi wire mai same reistance hoga jo ki absolutely nhi hota hai isi liye ise specific resistance bhi kehte hai kyoki ye material pr depend krti hai na ki length aur area pr. Iske liye jo symbol use hota hai use rho kehte hai upar likha hai dekh lena.
Ab resistance aur resistivity dono hi temperature pr depend krti hai. Kaise krti hai ye tumhare syllabus mai nhi hai lekin 12 mai hai jise jan na hai vo science le lena. Aur alloys ke bare mai book mai likha tha is liye likh diya nhi to aage ek topic aayega heating effect usme dobara se likh dunga ki unki resistance metals ke comparison mai jyada hoti hai aur vo high temperature pr burnout bhi nhi hote isi liye unhe heaters wagera mai use krte hai. Aur bulb ka filament tungsten se bna hota hai ye viva mai mere se bhi pucha tha 12 ke. Ye yaad rakhna basic knowledge hai. Kyo tungsten ka iska simple sa reason hai ki tungsten ka melting point sabse jyada high hota hai. Par aaj kal to led bulbs aa gaye jo energy bhi kam use krte hai aur na filament ki jarorat hoti. Iske question bhi dekh lena ek do lekin mainly question aayenge agle topic se jo mai agle part me cover karunga aur ek do questions bhi karna padenge kyoki vo topic aise hi samjh nhi aayega. Chalo ye part to bahut chota tha agle part ke liye taiyar rehna vo isse bhi chota hoga. Agar book ke numericals ka bhi solution isi tarah chahiye to comment kr dena. )
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