---
title: "Temperature difference across insulating layer, 1600 W"
subject: "Fundamental of Thermodynamics & Heat Transfer"
chapter: 7
key: "semester_2/fundamental_of_thermodynamics_and_heat_transfer:insulating-layer-temp-difference-1600w"
source: https://www.bctengineer.com/q/semester_2/fundamental_of_thermodynamics_and_heat_transfer/insulating-layer-temp-difference-1600w
site: BCT Engineering
---

# Temperature difference across insulating layer, 1600 W

Fundamental of Thermodynamics & Heat Transfer · Chapter 7: Introduction to Heat Transfer

- Asked in: 2073 Bhadra, 2 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/fundamental_of_thermodynamics_and_heat_transfer/insulating-layer-temp-difference-1600w
- Whole chapter: https://www.bctengineer.com/md/semester_2/fundamental_of_thermodynamics_and_heat_transfer/chapter-7

## Question

The magnitude of heat transfer through an insulating layer, 0.8 m² surface area, 5 cm thick and having a thermal conductivity of 0.25 W/mK is found to be 1600 W. Determine the temperature difference existing across the material.

## Answer

**Given:** A = 0.8 m², L = 5 cm = 0.05 m, k = 0.25 W/m·K, Q = 1600 W.

Fourier's law for a plane layer: Q = kA ΔT/L

ΔT = Q L/(kA) = 1600 × 0.05/(0.25 × 0.8) = 80/0.2

**Answer: ΔT = 400 K (400 °C) across the insulating layer.**

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which law gives heat flow through a plane layer?
   A. Stefan-Boltzmann law
   B. Ohm's law only
   C. Fourier's law Q = kAΔT/L
   D. Newton's law of cooling
   Answer: C. Conduction through a plane layer follows Fourier's law. (Key point: Governing law)

2. ΔT in terms of Q is
   A. Q k A/L
   B. Q L/(k A)
   C. k A/(Q L)
   D. Q A/(k L)
   Answer: B. Rearranging Q = kAΔT/L gives ΔT = QL/(kA). (Key point: Rearrangement)

3. ΔT with Q = 1600 W, L = 0.05 m, k = 0.25, A = 0.8 is
   A. 40 K
   B. 4000 K
   C. 400 K
   D. 100 K
   Answer: C. 1600 x 0.05 / (0.25 x 0.8) = 80/0.2 = 400 K. (Key point: Result)

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