A resistance-meter has five measurement range-settings between 200 Ω and 2 MΩ in multiples of 10. The meter measures resistance

Q. A resistance-meter has five measurement range-settings between 200 Ω and 2 MΩ in multiples of 10. The meter measures resistance of a device by measuring a full-range voltage of 2 V across the device by passing an appropriate constant current for each range-setting. If a device having a resistance value in the range 8 kΩ to 12 kΩ and a maximum power rating of 100 µW is to be measured safely with this meter, the choice for range-setting on the meter for best resolution in measurement, in kΩ, is

             (A) 2               (B) 20                          (C) 200                        (D) 2000

Ans: 200

Sol:

Resistance to be measured
⇒ 8 kΩ to 12 kΩ

So, minimum range should be 20 kΩ.

With 20 kΩ range: