This question was previously asked in

ISRO (VSSC) Technician Electrician Feb 2019 Official Paper

Option 1 : 0 Ω and ∞ Ω respectively

ME Subject Test 1: Strength of Materials

9166

20 Questions
20 Marks
18 Mins

- The ohmmeter is an instrument to measure electric resistance.
- Series type ohmmeter used to measure resistance which is in series with the ohmmeter.

The above figure shows a series type ohmmeter.

- R
_{1}is the current limiting resistor and R_{2}is the zero adjusting resistor. - The pointer of ohmmeter works on the D’Arsonval movement principle.
- E is the source voltage, R
_{m}is the internal resistance of D’Arsonval movement and R_{x}is the resistance to measure. - Where there is no resistance then-current drawn by the circuit will be maximum and water will show deflection, by adjusting R
_{2}. - i.e. for full scale current deflection, the value of resistance R
_{x}= 0 Ω - And the corresponding pointer indication is marked as zero at this time.
**Now, terminal AB is opened which provides very high resistance, and hence almost zero current will flow through the circuit.****i.e. for zero indication of current, the value of resistance would be infinite (R**_{x}= ∞ Ω)

__Note:__

- This method is good but it possesses some limitations such as the decreases in Emf of the battery, the meter may not read accurately.
- This problem may be counteracted by the adjustable resistance in series with the battery.