A good voltmeter needs to have very high internal resistance (why?).
Answers
HELLO THERE!
Thank you very much for asking this question, it is really a logical one.
A voltmeter needs to have a very high resistance.
Reason: Voltmeter must have a very high (infinite) resistance to avoid loading effect (the degree to which a measurement instrument impacts electrical properties (voltage, current, resistance) of a circuit). If the resistance of voltmeter is low, it will start acting as a load itself and hence, will draw heavy current from the source of power (battery, cell, etc). Since voltmeter is connected in parallel to the load, the current drawn by the actual load also changes.
We know, that V= IR, so, as current has changed through load, voltage also changes.
When voltmeter has very high resistance, it draws much less current from the power source, and the load current is the same as it was without the voltmeter. Hence voltage across the load is approximately same and we get the correct voltage reading, while experimentation to find the amount of voltage supplied by the source.
HOPE MY ANSWER IS SATISFACTORY...
Thanks :)