An electric heater supplies heat to a system at a rate of 120 W. If system performs work at a rate of 80 J s-1, the rate of increase in internal energy is

Question

An electric heater supplies heat to a system at a rate of 120 W. If system performs work at a rate of 80 J s-1, the rate of increase in internal energy is (A) 30 J s-1 (B) 40 J s-1 (C) 50 J s-1 (D) 60 J s-1

Tardigrade Admin · Accepted Answer

According to first Law of thermodynamics Δ Q = Δ U +Δ W ∴ (Δ Q/Δ t) = (Δ U/Δ t) +(Δ W/Δ t) Here, (Δ Q/Δ t) = 120W, (Δ W/Δ t) = 80 J s-1 ∴ (Δ U/Δ t) = 120-80 = 40 J s-1

Q. An electric heater supplies heat to a system at a rate of $120 W$ . If system performs work at a rate of $80 J s^{- 1}$ , the rate of increase in internal energy is

$30 J s^{- 1}$

$40 J s^{- 1}$

$50 J s^{- 1}$

$60 J s^{- 1}$

According to first Law of thermodynamics
$Δ Q = Δ U + Δ W$
$∴ \frac{Δ Q}{Δ t} = \frac{Δ U}{Δ t} + \frac{Δ W}{Δ t}$
Here, $\frac{Δ Q}{Δ t} = 120 W,$
$\frac{Δ W}{Δ t} = 80 J s^{- 1}$
$∴ \frac{Δ U}{Δ t} = 120 - 80 = 40 J s^{- 1}$

Q. An electric heater supplies heat to a system at a rate of 120W. If system performs work at a rate of 80Js−1, the rate of increase in internal energy is

30Js−1

40Js−1

50Js−1

60Js−1