Which of the following instruments has the highest internal resistance?

CONCEPT:

• Voltmeter: The electrical instrument which is used to measure the potential difference between two points in an electric circuit is called a voltmeter.
  • The Voltmeter is connected in parallel in an electric circuit.
• Galvanometer: It is used to detect the presence of a small electric current and voltage. It is connected in series.
• Ammeter: The electrical instrument which is used to measure the electric current in an electric circuit is called an ammeter. 
  • An Ammeter is connected in the series combination because the current remains constant in the series combination.
  • This helps in getting an accurate reading from the instruments.

EXPLANATION:

• ​An ideal voltmeter shouldn't be able to draw current from the circuit, hence the resistance of the voltmeter must be infinity.

• Ammeter has low resistance, ideally zero. By connecting the ammeter in series, it allows all of the circuit current to pass through it and hence measure it.

• In the case of the galvanometer, it is the same as that of the ammeter, since the galvanometer is used to find out the presence of current it must be having small resistance.

• From all the above discussions it is clear that from the given options voltmeter has the high resistance. Hence, option 1 is the answer

Mistake Points 

• Difference between Ammeter and Galvanometer:

1. The ammeter shows only the magnitude of the current.
2. The galvanometer shows both the direction and magnitude of the current.