Using the formula H=I*I*R*T we get H is directly proportional to R.
but also in the second formula we have H=(V^2/R)T.. here R is inversely proportional to R. HOW IS THIS POSSIBLE??? IS R DIRECTLY OR INVERSELY PROPORTIONAL TO H
(H=HEAT, I=CURRENT,T=TIME,V=POTENTIAL DIFFERENCE)
Answers
We have a resistor of value R, that is connected across a potential difference V. Then a current of intensity I flows in that, where I = V / R. The power (instantaneous) dissipated as heat is = P = I² R or V² / R.
Then heat generated over time T is H = P T = I² R T = V² T / R
ANSWER:
Once we understand this much, we need to know if the resistance is connected across a current source which has a fixed current or across a voltage source like a battery. In this case the voltage is constant.
In case the voltage V across R, is constant, then H is inversely proportional to R. In this case the current varies inversely with R and hence we have to substitute I = V/R...
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In case the current passing through R, is kept constant, then voltage across it varies directly as R varies, then we use the formula : H = I² R T. Then H is directly proportional to R.
answer;
in the formula H=i2rt.. it's the case of series.. where I is constant and heat will be directly proportional to I.. in the second case... where H= v2/r t... it's the case in parallel.. where v is constant for given time... h is Inversely proportional to r...
there is one question for u...
A student boils the water in an electric kettle for 20 minutes. Using the same main supply, he wants to reduce the boiling time of water. To do so, should he increase or decrease the length of the heating element? Justify your answer.
in this there is case of parallel.. we will judge according to v2/r t...
The length of a conductor is directly proportional to its resistance,
we would have to increase heat to reduce time... so will reduce resistance..
to reduce the heating time on the same supply, we must reduce the length