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A galvanometer coil has a resistance of 10 Ω and the meter shows full scale deflection for 3 mA. The value of shunt to convert this meter into ammeter of range 0 to 10 A is ______ ×10⁻³ Ω.

Asked in GSEB Board March 2023 · Conversion to ammeter and voltmeter

• (1) 3
• (2) 2
• (3) 1
• (4) 4

Step-by-step solution

Why the other options are wrong

• (2) 2×10⁻³ Ω is the shunt for a 2 mA movement. With the 3 mA this meter actually has, S=(I_gG)/(I-I_g)=3.0×10⁻³ Ω.
• (3) 1×10⁻³ Ω is the shunt for a 1 mA movement, or for a coil of (10)/3 Ω. The data here give 3 mA and 10 Ω.
• (4) 4×10⁻³ Ω is the shunt for a 4 mA movement. Note too that dividing by I-I_g rather than by I matters only in the fourth figure here, since I_g is 3 mA out of 10 A.

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