The amount of heat Q, which flows from the hot face to the cold face of a material of the slab is given by
(1) \(Q = \frac {KA(T_1 - T _2)t}{d}\)
(2) \(Q = \frac {KA (T _1 - T_2)d}{t}\)
(3) \(Q = \frac {K(T_1 - T_2)t}{Ad}\)
(4) \(Q = \frac {A(T_1 - T_2)d}{Kt}\)