Published by:
CGP EDU Academic Team
Published on: September 12, 2026
A totally black spherical space probe is very far from the solar system. As a result of heating by a nuclear energy source of strength I inside the probe, its surface temperature is T. The probe is now enclosed within a thin thermal protection shield, which is black on both sides and attached to the probe's surface by a few insulating rods. Find the new surface temperature of the probe. Determine also the surface temperature which would result from using N such shields.

Text Solution
Verified by ExpertsThe correct answer is:
A
Step 1: For a black spherical object, the power absorbed due to the nuclear source is given by the Stefan-Boltzmann law: \( P = \sigma A T^4 \), where \( A \) is the surface area of the sphere and \( \sigma \) is the Stefan-Boltzmann constant.
Step 2: With the thermal protection shield, the system can be treated as two black bodies in series. The temperature of the probe will be affected by the added thermal barrier.
Step 3: Assuming a uniform temperature distribution, the effective temperature of the probe plus one shield can be modeled using the effective thermal resistance. For one black shield, the new surface temperature \( T' \) of the probe can be expressed as \( T' = T \left(\frac{1}{2} \right)^{1/4} = T \cdot \left( \frac{1}{\sqrt{2}} \right) = \frac{T}{\sqrt{2}}.
Step 4: Extending this logic, with \( N \) shields, the temperature of the probe would further decrease: \( T_{N} = T \cdot \left(\frac{1}{\sqrt{2}} \right)^{N}.
Therefore, the final expression shows that the probe's surface temperature decreases with the number of shields, producing a perfectly insulated effect with increasing layers.
Step 2: With the thermal protection shield, the system can be treated as two black bodies in series. The temperature of the probe will be affected by the added thermal barrier.
Step 3: Assuming a uniform temperature distribution, the effective temperature of the probe plus one shield can be modeled using the effective thermal resistance. For one black shield, the new surface temperature \( T' \) of the probe can be expressed as \( T' = T \left(\frac{1}{2} \right)^{1/4} = T \cdot \left( \frac{1}{\sqrt{2}} \right) = \frac{T}{\sqrt{2}}.
Step 4: Extending this logic, with \( N \) shields, the temperature of the probe would further decrease: \( T_{N} = T \cdot \left(\frac{1}{\sqrt{2}} \right)^{N}.
Therefore, the final expression shows that the probe's surface temperature decreases with the number of shields, producing a perfectly insulated effect with increasing layers.
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