Question -
Seven resistors each of resistance 5 ohm are connected as shown in figure. The equivalent resistance between points A and B is
Options:
A .  1 ohm
B .  7 ohm
C .  35 ohm
D .  49 ohm
Answer: Option B : B The circuit can be redrawn as shown in figure. Let a bettery of emf E and of negligible resistance be connected as shown. The current in various branches are shown.Applying Kirchoff's second law to loops ACDA,CBDC and ADBGFA we have 5i2+5i3−10i1=0 10(i2−i3)−5(i1+i3)−i3=0 10i1+5(i1+i3)−E=0 equation (i) and (ii) give i2=3i12 and i3=i12. If R is the effective resistance between A and B then R=Ei1+i2=2E5i1 from equation (iii) we have E=15i1+5i3=35i12 R=2E5i1=2∗35i15i1∗2=7 Ohm
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