The Figure shows the arrangement of five identical bulbsR1 ,R2 ,R3 ,R4 and R5
a) When the switch is closed will all the bulbs glow? Give reason.
b) Identify the underlying principle. Deduce the principle for a resistance network.
a) No. Since all the bulbs are identical the bridge is balanced. So potential at B and C is
same and no current flows through the bulb connected between B and C. So all other
bulbs except R 5 will glow.
b) Wheatstone’s principle.
The bridge has four resistors R1 , R2 , R3 and R4 . A source is connected. There will be
currents flowing through all the resistors as well as the galvanometer. In the case of a
balanced bridge Ig = 0.Then
Kirchhoff’s junction rule applied to junctions D and B gives
I 1 = I 3 and I 2 = I 4 .
Kirchhoff’s loop rule to closed loops ADBA