Question text1. The one-dimensional heat flow equation is: [math: ρCP∂T∂t=κ∂2T∂z2+A] where ρ, Cp, and κ are the density, specific heat and thermal conductivity, and A represents heat sinks and sources. The boundary conditions in a given system are: (i) T=320 K at z=0 (ii) T=1200 K at z=40 km and we also have [math: κ=3Wm−1K−1]. Assuming no internal heat sources, calculate a) The thermal gradient of the equilibrium geotherm in [math: K/km] to two significant figures.Thermal gradient = Answer 1 Question 3[input] [math: K/km] [6] b) The temperature at a
depth of 100km as predicted by this geotherm model. Give answer in K to two significant figures. T(z=100 km) = Answer 2 Question 3[input] K [4]

Question

Question text1. The one-dimensional heat flow equation is: [math: ρCP∂T∂t=κ∂2T∂z2+A] where ρ, Cp, and κ are the density, specific heat and thermal conductivity, and A represents heat sinks and sources. The boundary conditions in a given system are: (i) T=320 K at z=0 (ii) T=1200 K at z=40 km and we also have [math: κ=3Wm−1K−1]. Assuming no internal heat sources, calculate a) The thermal gradient of the equilibrium geotherm in [math: K/km] to two significant figures.Thermal gradient = Answer 1 Question 3[input] [math: K/km] [6] b) The temperature at a
depth of 100km as predicted by this geotherm model. Give answer in K to two significant figures. T(z=100 km) = Answer 2 Question 3[input] K [4]

BlackTom AI · Accepted Answer

The problem gives the one-dimensional heat flow with no internal sources and asks for the thermal gradient of the equilibrium geotherm and the temperature at 100 km depth. Since there are no internal heat sources (A = 0) and we’re likely dealing with a steady state (no explicit time dependence in the equilibrium geotherm), the equation reduces to κ d^2T/dz^2 = 0, which means d^2T/dz^2 = 0 and the temperature varies linearly with depth.

- Step 1: Compute the thermal gradient (dT/dz) from the boundary conditions. With T = 320 K at z = 0 and T = 1200 K at z = 40 km, the gradient is
  dT/dz = (T2 − T1) / (z2 − z1) = (1200 K − 320 K) / (40 km − 0 km) = 880 K / 40 km = 22 K/km.
  This matches the expectation for a linear geotherm under steady-state conduction with no internal sources.

- Step 2: Use the gradient to find the temperature at z = 100 km. Starting from z = 0 with T = 320 K and increasing by 22 K per km, we have
  T(z = 100 km) = T(0) + (dT/dz) · z = 320 K + (22 K/km) × 100 km = 320 K + 2200 K = 2520 K.

- Step 3: Apply significant figures. The gradient was computed as 22 K/km, which is already two significant figures. The temperature at 100 km, 2520 K, should be expressed to two significant figures as 2.5 × 10^3 K, i.e., 2500 K, to align with two-significant-figure notation.

Notes:
- If a provided reference answer shows 2540 K for T(100 km), that would imply a gradient of 22.0 K/km and/or a different base temperature or rounding choice; however, with the given boundary conditions (320 K at z = 0 and 1200 K at z = 40 km), the physically consistent result is 2520 K, i.e., 2500 K to two significant figures.

GEOL0012_25-26 GEOL0012 Moodle Test (unassessed) 2025/26

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