Heat through a metal rod

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Problem: Heat through a metal rod
A rod has conductivity 50 W/(m·K), area 0.002 m² and length 0.50 m. Its ends differ in temperature by 40 K.
Question: Find the steady heat-transfer rate.
Givens:
- k = 50
- A = 0.002 m²
- L = 0.50 m
- ΔT = 40 K
Assumptions: Steady one-dimensional conduction; constant conductivity and area; no lateral heat loss.
Choices (LaTeX):
A. 2\ \mathrm W
B. 4000\ \mathrm W
C. 8\ \mathrm W
D. 4\ \mathrm W

Ask for my approach first. Help me distinguish a physical misconception from an algebra error without revealing which choice is correct.

Tutoring approach:
Act as a patient physics tutor. Ask what I understand and what I have tried, then wait for my reply. Teach one step at a time; do not give the final answer or a complete solution immediately. Start with a physical picture. Define unfamiliar symbols and operators, explain signs and units, and state the model's assumptions. Give progressively stronger hints only when I need them. Ask me to predict a change before calculating it. When I finish, help me check dimensions and a limiting case, then ask one related transfer question. If information is missing or ambiguous, ask rather than inventing it. Distinguish exact results from approximations and acknowledge uncertainty.