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A coil of the electric heater with a resistance of $20\Omega$ is immersed in 1 kg of oil, current of magnitude 5 A is passed through the coil, after 30 seconds of heating, the coil raises the temperature of the oil by 20 K. What is the specific capacity (in J/kgK) of the coil?
Option: 1
15000

Option: 2
7500

Option: 3
45000

Option: 4
3000

Answers (1)

best_answer

Heat energy is related to specific heat capacity as,

$H=mC\Delta T$

Here m is the mass of the substance

C = specific heat capacity of the substance

$\Delta T=$ change in temperature

Given,

m = 1 kg

$\Delta T=20K$

Heat provided by Heater per second,

$P=I^{2}\times R$

Here

$I = current = 5A$

$R = Resistance =$ $20\Omega$

Heat provided by the heater in $30$ seconds,

$H=P\times t=I^{2}\times R\times t$

$H = 5^2\times20\times30 = 15000 J$

Also $H=mC\Delta T$

Putting in the equation,

$15000=mC\Delta T$

$15000 = 1\times C\times 20$

$\mathrm{C = 7500 \ J/kgK}$

Hence, Option number (2) is correct

Posted by

manish painkra

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