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A 50 mm x 45 mm x 20 mm cell phone charger has a surface temperature of T,-330C when plugged into an electrical wall outlet but not in use. The surface of the charger is of emissivity ε = 0.92 and is subject to a free convection heat transfer coefficient of h 4.5 W/m2, K. The room air and wall temperatures are T.-220C and Tsur-200C, respectively Tsur w 20 mm L = 50 mm Wall ir Charger T, h

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