Abhyaas Series Ep 18 | JEE Advanced 2026 | Physics Paper 2 Q2

Episode 18 of the Abhyaas Series is here. A nuclear reactor produces a radioactive nuclide at a constant rate. The nuclide decays and each decay releases energy that heats a liquid. Find the rate of increase of temperature of the liquid as a function of time. This question sits at the intersection of nuclear physics, thermodynamics and differential equations and it is exactly the kind of problem where students pick the wrong answer because they confuse the number of nuclides present with the rate of decay. Those are not the same thing and conflating them is the most common mistake here. The number of nuclide atoms present at any time t is not simply alpha times t. The reactor produces them at rate alpha but they are simultaneously decaying at a rate that depends on how many are present. That competition between production and decay gives you a first order differential equation whose solution is the well known production-decay formula. Once you have the number of atoms present at time t, the activity at that instant is lambda times that number, and that activity multiplied by E0 gives the power going into the liquid. The rate of temperature increase follows directly from that power and the heat capacity of the liquid. Visualise the production and decay dynamics of the nuclide interactively here: https://abhyaas-series.vercel.app/ What we cover in this video :- Setting up the differential equation for the number of nuclide atoms present at time t Solving the production-decay equation to get the number of atoms as a function of time Finding the activity of the nuclide at time t using the decay constant Connecting activity to power delivered to the liquid Deriving the rate of temperature increase and matching to the correct option Why options B, C, and D are wrong and exactly where each one goes off track. Concept used: Nuclear Physics, Radioactive Decay, Production-Decay Equation, Calorimetry Source: JEE Advanced 2026 | Physics Paper 2 | Q2 Interactive visualisation of radioactive production and decay dynamics: https://abhyaas-series.vercel.app/ If this helped, share it with your JEE prep group. Subscribe for the full Abhyaas Series covering every JEE Advanced 2026 Physics question one by one.