Which of the following instrument has an internal power source?

Ohmmeter:

• It is an electrical instrument that is used to measure electrical resistance.

• Micro-ohmmeter is used to measure low resistances.
• Mega-ohmmeter is used to measure high resistances.
• Working: Ohmmeter measure resistance by passing a small current to the sample and measure the voltage drop across it and find the resistance with the help of ohm’s law i.e V = IR.

• R_x = unknown resistance whore resistance is to be measured.
• The instrument is connected to the battery V whose internal resistance is R_a.
• Where the circuit is completed by connecting R_n then the current flows and so the deflection is measured.
• Ohmmeter works on the principle of the D’arsonal movement.
• When a current-carrying coil placed in a magnetic field, it feels a force that can deflect the pointer of the meter and thus we get the reading.

Types of ohmmeter:

1) Series ohmmeter: In this measuring resistance component is connected in series of the instrument.

2) Shunt ohmmeter: In this meter, the measuring resistance is connected in parallel with the battery.

3) Shunt ohmmeter used to measure mainly low resistance.

4) Multi-range ohmmeter: The range of this type of meter is very high. It has adjuster which selects the range according to the need.

5) multirange ohmmeter is the most suitable and widely used meter.

Voltmeter: It is an instrument used for measuring electrical potential between two points of the circuit.

Ammeter: It is an instrument used to measure current in electrical circuits.