Q.

The heat transfer by conduction through a thick sphere is given by

• AQ = 2πkr1 r2 (T1 - T2)/ (r2 - r1)
• BQ = 4πkr1 r2 (T1 - T2)/ (r2 - r1)
• CQ = 6πkr1 r2 (T1 - T2)/ (r2 - r1)
• DQ = 8πkr1 r2 (T1 - T2)/ (r2 - r1)