a) use kirchhoff's rules , calculate the current in the arm AC of the given circuit. (b) on what principle does the metre bridge work? why are the metal strips used in the bridge ?​

 

Dear Student,

(a)


Applying kirchoff's junction rule at A node,I3=I1+I2  ......(1)Applying kirchoff's second rule in loop EFCA,-30I1+40-40I3=0  3I1+4I3=4 .....(2)In loop EFDB,-30I1+20I2-80=0-3I1+2I2=8 .....(3)from equation (1) put the value of I3 in equation (2),3I1+4I1+I2=47I1+4I2=4  .....(4)from (3) and (4),13I1=-12I1=-1213 APut I1 in equation (4),7×-1213+4I2=44I2=4+8413I2=3413 Afrom equation (1),I3=-1213+3413I3=2213 A

(b) Metre bridge works on the principle of Wheat stone bridge. The thick metal strips are used to minimise the resistance of connection wires, because the connection resistance have not been accounted in the formula. (resistance is inversely proportional to cross section area, so thick wire has low resistance, moreover the resistivity of copper is small compared to manganin.
 

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