Question

what is a voltameter?

Answer 1

voltmeter. An electrical instrument for measuring voltage. Originally it was a Galvanometer connected in series to a high resistance and although it measured current it can be calibrated in volts.

Answer 2

what role does the high resistance play in the circuit & how?

Answer 3

the high resistance keeps the current low enough so it doesn't burn out the galvanometer and to increase voltmeters input resistance so when used to measure a voltage does not take to much current from the measured circuit.

Answer 4

and why we use low resistance for ammeter?
wouldn't that high current burn the galvanometer?
& why galvanometer doesn't want too much current to measure voltage?

Answer 5

Remember the galvanometer (g-m) has a max safe working current and buy itself has a limited current measuring range. like 100 uamps. To be able to measure higher currents you must place a low resistance resistor called a shunt in parallel with the . Most of the(g-m) current you are measuring goes through the shunt the rest through the (g-m). What goes through the (g-m) is proportional to the current entering the shunt/(g-m) circuit. and therefore can be calibrated for larger currents.

For a voltmeter the high resistance is put in series to reduce the current the (g-m) circuit takes for the circuit whose voltage you are measuring. If you take too much current from the device whose voltage you are measuring by Ohms law you change the voltage you are measuring creating an error.

Answer 6

but sir since the (g-m) & high resistance are placed in series so same current will be passing through both of them,how can large or small amount of current can effect the voltage since the same amount of current is passing either it is high or low?

Answer 7

When you measure a voltage with a voltmeter you must divert a little current from the device whose voltage you a measuring. The R connected in series with the G-M must be large compared to Rd so as to minimize the reduction of I that should be flowing through the device. The resistance of the G-M is usually too low to allow the G-M to be used to measure the voltage by itself. R>>rg. so that I very close to Id. Normal voltmeters are never exact.