Homework Help: Potential difference

tin llenaresas · Sep 17, 2005

what happens to the potential difference of a source of emf when a voltmeter is connected across its terminals?
tanx.

Tide · Sep 17, 2005

HINT: Does current flow when the voltmeter is connected?

tin llenaresas · Sep 17, 2005

hey tide,

ideal voltmeters should have infinite resistance so as not to alter current but real voltmeters have finite resistance.does our voltmeter, in any way, still alter the current flowing through our set-up?

Tide · Sep 17, 2005

I assume that the source of EMF that you have in mind is a battery. Batteries have internal resistance and if there is current flowing through the battery then, by Ohm's Law, there must be a potential difference across the resistance.

tin llenaresas · Sep 18, 2005

so, does the voltmeter affects the potential difference of a source?

mukundpa · Sep 18, 2005

Yes, the potential difference across the battery will decrease but still the emf of the source remains the same. The emf of a source is the energy supplied by the source per unit charge and is measured by the potential difference across the terminals, when no current is flowing through the source.