A. How many atoms would be present in a black dot marked on the paper with graphite pencil as a full stop at the end of a sentence? [Given mass of a dot = 10-18 g]
b. Write the cations and anions present (if any) in the following compounds:
(i) CH3COONa
(ii) NaCl

the answer is option a.

answer: semi-infinite solid initially at a uniform temperature of 400 ◦c is cooled at its surface by convection. the cooling fluid at a constant temperature of 200 ◦c has a convective coefficient (ha) of 250 w/m2.k. the physical properties of the solid: k = 20 w/m.k and α = 4 * 10-5  m2/s. using δx = 0.04 m and δt = 10 s. write the finite difference equations describing the transient heat transfer of the first five δx and the temperature profile after 30 s.