Heat Equation for No Heat Loss at x=a

[punkstart]

The question :Two rods L1 and L2 of different materials( hence different thermal conductivities) and different cross-sectional areas,are joined at x=a. The temperature is continuous,
And NO HEAT ENERGY IS LOST AT a, so all heat energy that flows from L1 flows into L2.

? What equation represents the condition that no energy is lost at a ?

My thoughts : Equate the rate at which heat leaves L1 to the rate at which heat enters L2. ?

 

[ideasrule]

Yes.