in the meter bridge shown in figure, initially P/Q = 1. Find the shift in the null point if P is doubled and Q is halved.

If l be the initial distance of the null point from end A, then Pl=Q100-l⇒l=100QP+1Initially, l=1001+1cm=50 cmFinally l'=10014+1cm=80 cm∴  shift=l'-l=80 cm - 50 cm = 30 cm