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Sahay Sir > Question Answers > Uncategorised (JEE Advanced Physics by BM Sharma + GMP Solutions) > The walls of a closed cubical box of edge 40 cm are made of a material of thickness 1 mm and thermal conductivity 4×10^−4 cal/s∘C−1. The interior of the box is maintained at 100∘C above the outside temperature by a heater placed inside the box and connected across 400 V dc . Calculate the resistance of the heater.

The walls of a closed cubical box of edge 40 cm are made of a material of thickness 1 mm and thermal conductivity 4×10^−4 cal/s∘C−1. The interior of the box is maintained at 100∘C above the outside temperature by a heater placed inside the box and connected across 400 V dc . Calculate the resistance of the heater.

An electric motor operating on a 50 V dc supply draws a current of 12 A. If the effenciency of the motor is 30 % estimate the resistance of the windings of the motor .