Express the change in internal energy of a system when

(i) No heat is absorbed by the system from the surroundings, but work (W) is done on the

system. What type of wall does the system have

(ii) No work is done on the system, but a amount of heat is taken out from the system and given

to the surroundings. What type of wall dues the system have ?

(iii) w amount of work is done by the system and q amount of heat is supplied to the system. What

type of system would it be ?