What is the Resistance of R1 in a Dual Range DC Milliammeter?

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SUMMARY

The discussion focuses on calculating the resistance of R1 in a dual range DC milliammeter setup. The moving coil meter has a resistance of 50 ohms and achieves full-scale deflection at 1.0 mA. When connected to terminals A and C, a current of 20 mA results in full-scale deflection, leading to the equations R1 + R2 = 50 ohms and 1(50) = 19R1 + R2. The user concludes that R1 cannot equal zero, indicating a need for further analysis of the circuit configuration.

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  • Understanding of Ohm's Law and circuit analysis
  • Familiarity with moving coil meters and their specifications
  • Knowledge of series and parallel resistor configurations
  • Basic proficiency in setting up and solving equations in electrical engineering
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Electrical engineering students, hobbyists working with analog meters, and professionals involved in circuit design and analysis will benefit from this discussion.

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Homework Statement



The figure shows a dual range dc milliammeter which has a common negative terminal A and positive terminal B and C . The indiacator is a moving coil meter of resistance 50 ohm which gives full scale deflectino with a current of 1.0 mA . When connection ismade with the terminals A and C , a current of 20 mA gives full scale deflection . What is the resistance of R1 ?

Homework Equations





The Attempt at a Solution



when A and B are connected to a circuit , R1+R2=50 ohm

when A and C are connected to a circuit ,

1mA will flow through the resistor R2 , then to the meter while 19 mA will flow through resistor R1 .

and pd across meter = pd across shunt

1(50)=19R1+R2 ---1

R1+R2=50 ----2

and R1=0 ??

Cant be !
 

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is there anything wrong with my work ?
 

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