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Question

In the circuit in figure, we have R2=20Ω , R3=15Ω, and the current flowing through resistor R2 is 0.3 A. The ammeter shows 0.8 A. Find the resistance R1 :
131854.png
  1. 20Ω
  2. 30Ω
  3. 40Ω
  4. 60Ω

A
30Ω
B
60Ω
C
20Ω
D
40Ω
Solution
Verified by Toppr

Potential drop across R2 = Potential drop across R1 = Potential drop across R3
Considering R2 and R3
i2R2=i3R3
0.3×20=15×i3
i3=0.4A
Current passing through ammeter =i1+i2+i3=0.8
i1+0.3+0.4=0.8
i1=0.1A
PD across R1 should be equal to the potential drop across R2
i1R1=i2R2
0.1R1=0.3×20
R1=60ohm
Hence option D is correct.

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