A meter bridge works on the principle of a Wheatstone bridge. In a meter bridge, we need to adjust the resistances and have a balance point in the middle of the bridge.
For a balanced meter bridge, we have the following equation
Therefore, for balance point to lie in the middle, l1 = 50cm, this means R=S.
To find R, we again use the above equation, where S=100, l1 = 2.9cm.
Therefore, he should change the resistance to 3Ω.
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