how is duration affected by a fall in interest rates?

Answer 1

"Duration" is not affected by interest rates. It is a measure of a bond's sensitivity to a change in interest rates. For example, a 5-year zero coupon bond will have a duration of 5. It will remain at 5 regardless if rates rise or fall, gradually falling to zero as time passes toward maturity.

Now if you are talking about "Macaulay Duration" or "Modified Duration", those are affected by falling interest rates as the price of a bond (which is affected by interest rates) is used in their calculation.

Answer 2

Umm...duration of what?