The need or want for a particular product becomes a demand when
Answers
Need, want, demand seems to be very closely related words, however they all differ with respect to their meaning.
Need - necessity. Something that is required to survive or to sustain. For example, food, water, shelter etc.
Want - desires. Things without which we can survive, but we need them for higher satisfaction. For example, i want iphone 6S, though I can do without it.
(Human wants are unlimited! As one want is satisfied, a new one is created.)
Demand - willing and able to buy. Things that you want to buy/consume and your pocket allows its consumption, i.e you can afford it, thus you demand that thing. For example, I have Rs. 1000 in my pocket and I want to see a movie whose ticket is worth Rs 500, since I want it and I can afford it, I demand a movie ticket.