Ammeter & Voltmeter

A fraction of milliohm

The amount of resistance an ammeter should have.

Otherwise the equivalent resistance of the circuit would change and modify the current being measured.

Voltmeter

The meter inside our cell phones that indicates to us the percentage of the battery.

Are also used inside the automobile dashboards, to indicate the fuel level and the temperature gauge

Digital voltmeters

Convert the analog voltage into a digital value to display on a digital readout.

Terminal voltage

The voltage that is measured by the voltmeter between the positive terminal and the negative terminal of the battery or voltage source.

internal resistance

It is not possible to connect a voltmeter directly across the emf without including the ________________ of that battery

fuse

Ammeter normally contains a ____ to protect the meter from damage from currents that are too high.

Rm = 10 MΩ

Internal resistance of the inexpensive voltmeters.

Rm = 10 GΩ

Internal resistance of the high-precision voltmeters.

Galvanometer

Used by analog voltmeters/ammeters

A coil of wires, with a small resistance, in a magnetic field, with a pointer attached that points to a scale.

Current flows through the coil, causing the coil to rotate

small resistance, parallel

To use galvanometer as an ammeter, a _______________ is placed in ________ with the coil.

large resistance, series

To use galvanometer as a voltmeter, a _______________ is placed in ________ with the coil.

Ohmmeter

Device to measure the resistance of a component or a device. Its operation is based on Ohm’s law

internal voltage source, across, current, galvanometer, Ohm’s law

Traditional ohmmeters contains an ______________________ that would be connected ______ the component to be tested, producing a _______ through the component, which was then measured by ____________, and then the resistance is deduced by using _________.

constant current source, current, voltage

Digital Ohmmeters use a ______________________ to pass _______ through the component, and then the _______ is measured

Yes, it is true

Is it true that you should never do the following things when you are measuring the resistance by ohmmeter:

1) Make sure the circuit isn’t live (with a voltage source connected and the current running through it) this can damage the meter.

2) The component getting measured must be isolated from the circuit in order to not measure the equivalent resistance.

measured, known

In the case of Ohmmeter, the voltage is known and is the current is ________ or the current is _____ and the voltage is measured.