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

  1. 750
  2. 7500
  3. 75000
  4. 75

Answers (1)

Resistance of coil ,R = 20 ohm
mass of oil , M = 1 kg
current passing through it , I = 5A
time taken , t = 30 sec

you know , heat dissipates , H = I²Rt
= 5² × 20 × 30 = 25 × 600 J

we also know, Q = Ms ?T
here M is the mass of water , s is specific heat capacity. and ?T is the temperature.
so, Q = 1 × s× 20

now, Q = H
1 × s × 20 = 25 × 600
s = 750 J/kgK

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