Demand and Quatity demanded?

What is the difference between a "change in demand" and a "change in quantity demanded"? Between a "change in supply" and a "change in quantity supplied"? Give an example something that would cause a change in each.

change in quantity demanded refers to the movement of a point in the demand curve along the demand curve.change in demand refers to the shift in downward sloping demand curve either upward and downward.
suppose the price of one liter of milk is $ if price rise to $8 u might reduce the liter of milk purchased due to price rise.change in quantity demanded only occurs when there is a change in price.
change in demand can occur due to various reason other than could be due to change in the level of income, change in taste and fashion, windfall gains,etc.for example a fall in demand for cassettes has occurred due to the invention of CD and DVD.
change in quantity supplied only occurs due to change in price while change in supply would occur for any reason other than price like innovation, new production technique, fall in the cost of factors of production, spare capacity,etc
Just remember that Quantity demand is just a number; a point along the demand curve. A change in demand refers to the entire demand curve.

So a change in demand would shift the the curve. While a change in quantity demanded is just movement along the curve.

Ex. If the Supply curve moves to the right (supply increases) and and the demand curve doesn't: the Quantity demanded (the intersection of the two) would increase.
Ex2. If the people want to buy a good because it's fashionable (or something) then their would be a change in the demand curve to the right (demand increases).

Draw out some supply and demand curves and you'll see what's going on.
Does the language used in both phrases not explain the difference? I believe it does. A change in demand is that a certain product is no longer wanted because another is being bought instead while a change in quantity demanded, says that there is either less or more bought of whatever the product is.
So instead of Nokia phones people now want Ipod videophones and of Ipod nano┬┤s a lot less are sold because of the launch of Ipodvideophones.

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