Joule’s Law of Heating
According to Joule the amount of heat produced in a conductor due to the passes of current I is
1) directly proportional to the square of current.
i.e H ∝ I2 …….1)
,This is called joule’s first law of heating.
2) directly proportional to the resistance of a conductor
i.e. H ∝ R …….2)
This is called joule’s second law of heating.
3) directly proportional to the time for which current is passed through the conductor
i.e. H ∝ t …….3)
Combine equation 1,2 and 3,we get
H ∝ I2.R.t
H = K.I2.R.t
Experimental Verification of Joule’s law of Heating
The experimental arrangement for the verification of joules law of heating as shown in figure. it consists of a calorimeter, thermometer, heating element, Rheostate, ammeter as shown in figure.
A clean and dry calorimeter is taken and weighted about half of the calorimeter is filled with water and again weighted.A resistance wire is immersed in water through which current is passed.
1) To Verify H ∝ I2:
First of all,initial temperature of water and calorimeter is taken with the help of thermometer .let it be d1°C.The current I1 is passed through the resistance R in a time t and final temperature is Noted.let it be d2°c. the amount of heat produced is calculated by formula H=msΔd. Again Another current I2 is passed through the same resistance and same time and then amount of heat H2 is calculated, it is found that
H1/ I12 = H2/I22=Constant
so, H∝ I2
This is verified the Joule’s first law of heating.
2)To Verify H∝ R:
The same current is passed through different Resistance wire of resistance R1 and R2 in the same time t and then corresponding amount of heat produced H1 and H2 are calculated. it is found that,
H1/R1 = H2/R2 =constant
so, H∝ R
This verified the Joule’s second law Heating.
3)To Verify H∝ t:
The same current is passed through the same resistance wire in two different time t1 and t2 and then corresponding amount of heat produce H1 and H2 are calculated. it is found that,
H1/t1= H2/t2 =constant
so, H∝ t
This is verified the Joule’s third law of heating.
This is the required expression of verification of joule’s law of heating.
2)What do you meant by Shunt?What do you meant by Shunt? Describe its use in converting a Galvanometer into Ammeter.? Describe its use in converting a Galvanometer into Ammeter.
20)Magnetic Moment is
a) a scalar quantity
b) a vector quantity
c) universal constant