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For designing a voltmeter of range 50 V and an ammeter of range 10 mA using a galvanometer which has a coil of resistance 54 Ω showing a full scale deflection for 1 mA as in figure.
(A) For voltmeter R ≈ 50 kΩ
(B) For ammeter r ≈ 0.2 Ω
(C) For ammeter r = 6 Ω
(D) For voltmeter R ≈ 5 kΩ
(E) For voltmeter R ≈ 500 Ω
Choose the correct answer from the options given below.

Asked in JEE Main 15th April 1st Shift 2023 · Conversion to ammeter and voltmeter

• (1) (C) and (E)
• (2) (C) and (D)
• (3) (A) and (B)
• (4) (A) and (C)

Step-by-step solution

Why the other options are wrong

• (1) Wrong power of ten in R = V/I_g - G (used 0.5 V).
• (2) Used 5 V instead of 50 V for the voltmeter.
• (3) Right voltmeter, but wrong shunt: r = (I_gG)/(I - I_g) = (1 × 54)/9 = 6 Ω, not 0.2 Ω.

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