1. Calculate the resistances R1 and R2 in the figure that should be used to convert the galvanometer to a double-range ammeter deflecting full scale for currents of 100mA and 1 A.
2. Calculate the resistance of the ammeter of the figure for the 100 mA range.
3. Calculate the resistance of the ammeter of the figure for the 1 mA range.
Please show work!
Picture:
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✅ Answers
Answerer 1
You need info on the galvanometer, resistance and full scale voltage or current.
Answerer 2
The 2 resistors would need to be in the ratio of 10 of R2 to 1 of R1.
The meter should end up with 1V. across it for FSD. (standard figure).
The meter is in parallel with the 2 resistances in series, so at 100mA., the V across the resistances should also be 1V.
Ratio 10:1, so (1/11) = 0.090909V. across R1, and (1/11) x 10) = 0.90909V. across R2.
2) Resistance of circuit = (E/I) = 1/0.1, = 10 ohms on the 100mA. range.
Thus, the meter must have a resistance of 20 ohms, and the resistors also equal 20 ohms. So current through both paths is equal, = 50mA.
1) R1 = (0.090909/0.05) = 1.81818 ohms. R2 = (0.90909/0.05) = 18.181818 ohms.
3) (20 x 1.818181)/(20 + 1.8181) = resistance of 1.6667 ohms at 1A. range.