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प्रश्न
State how a moving coil galvanometer can be converted into an ammeter.
How will you convert a moving coil galvanometer into an ammeter?
Briefly explain why and how a galvanometer is converted into an ammeter.
उत्तर १
- A moving-coil galvanometer is transformed into an ammeter by connecting a low-resistance S across the coil and lowering its effective resistance.
- A shunt is a parallel low resistance that shunts a portion of the current around the coil, as seen in the image below. As a result, the range of currents over which the metre can be used is expanded.
Ammeter - Let I be the maximum current to be measured and Ig be the current for which the galvanometer of resistance G shows a full-scale deflection. Then, the shunt resistance S should be such that the remaining current I - Ig = IS is shunted through it.
- The potential difference across the galvanometer in the parallel combination is equivalent to the potential difference across the shunt.
∴ IgG = IsS = (I - Ig)S
∴ S = `("I"_"g"/("I" - "I"_"g"))"G"`
उत्तर २
Only small currents may be detected by a galvanometer. Thus, it is transformed into an ammeter to measure enormous currents. By joining a low resistance known as a shunt resistance in parallel with the galvanometer, it can be transformed into an ammeter.
Let S be the low resistance connected in parallel with the galvanometer, G be the resistance of the galvanometer, and I be the maximum current to be measured for full-scale deflection in the galvanometer. Since the galvanometer and shunt resistances are connected in parallel.
∴ The potential difference across 'S' = Potential difference across G
(I - lg)S = lgG
Notes
Students should refer to the answer according to their questions and marks.
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संबंधित प्रश्न
A rectangular coil of a moving coil galvanometer contains 50 turns each having area 12 cm2 . It is suspended in radial magnetic field 0.025 Wb/m2 by a fibre of twist constant 15 x10-10 Nm/degree. Calculate the sensitivity of the moving coil galvanometer.
A circular coil of 250 turns and diameter 18 cm carries a current of 12A. What is the magnitude of magnetic moment associated with the coil?
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Two moving coil meters, M1 and M2 have the following particulars:
R1 = 10 Ω, N1 = 30,
A1 = 3.6 × 10–3 m2, B1 = 0.25 T
R2 = 14 Ω, N2 = 42,
A2 = 1.8 × 10–3 m2, B2 = 0.50 T
(The spring constants are identical for the two meters).
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What are the advantages of using soft iron as a core, instead of steel, in the coils of galvanometers?
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A galvanometer coil has a resistance of 12 Ω and the metre shows full scale deflection for a current of 3 mA. How will you convert the metre into a voltmeter of range 0 to 18 V?
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