How can voltage be measured

The ammeter can be placed anywhere in the circuit. Remember that the current is the same in all parts of a series circuit. A voltage or potential difference across an electrical component, such as a lamp, is needed to make a current flow through it.

Cells or batteries often provide the voltage needed. This saves trying to probe two points at once. Probe the higher voltage point with the probe on the red lead. If necessary, adjust the range switch to obtain the best reading. Note the reading Either make the next reading or if finished remove the probes and turn the meter off. It is always best to return the meter range switch to the highest voltage range available as this could save damage of the meter is used before the proper range is set.

Inset the meter end of the probes into the required sockets Usually a meter will be provided with two leads, one black, and the other red. It is important to ensure that the negative lead is in the negative or common connection. Set the meter range to accommodate the largest expected value and allow a little extra as damage could result from high voltages or voltage reversal. Try to ensure that the positive voltage is applied to the positive lead as best as possible without actually probing.

Check that a positive deflection of the meter is obtained. Then adjust the multiuser range switch to reduce the value of the range. This is done until the largest deflection is seen on the meter without it going over the top of the range. In this way the most accurate reading is obtained. Note the reading Either make the next reading or if finished remove the probes. The units of such quantities are all relative to some commonly accepted standard, i. These quantities are relatively easy for us humans to understand.

But what about voltage and current? I understand how you can define electric fields experimentally - get a certain amount of charge on an object, and measure the force response felt by that charged object. Similarly with magnetic fields - send some charges through a magnetic field and measure their response. To measure the voltage across two points, I suppose you could connect some small "resistor" in between two points and measure how hot it gets under certain fixed conditions maintained within your measurement device.

I'm sure my intuition on all this "phenomenology" of voltage and current is based on 19th century equipment, but that's the only equipment I ever see intuitively broken down.

Modern electrical equipment is more mysterious owing to its inherent complexity I'm sure. Every time I try to look for an explanation of how multimeters really measure voltage and current, I'm met with circular explanations like "You measure voltage by connecting a resistor in parallel and measuring the voltage drop across it, or current passing through it" and "You measure current by connecting a resistor in series and measuring the voltage across it". Please, I just want an intuitive and direct answer.

An analog ammeter, called a galvanometer , passes current near a bar magnet which is physically attached to an indicator needle. A magnetic field surrounds the current, whose strength is proportional to the magnitude of the current, and so the angle of the needle changes.

A clever calibrator paints marks under different locations under the end of the needle corresponding to different currents in the galvanometer. Digital meters are based on the transistor. There are a lot of different devices which can be called "transistors," and a lot of configurations of the same transistor that can do different things. A common configuration is for the transistor to act as a current-controlled switch for bipolar transistors or as a voltage-controlled switch for field-effect transistors , where the current or voltage into the "base" terminal of the transistor determines whether the path between the "emitter" terminal and the "collector" terminal is insulating or conducting.

You can use a collection of transistors to build a comparator , a digital device whose output is "high" or "low" depending on which of its inputs is at higher voltage, and you can use a series of comparators with related reference voltages to build an analog-to-digital converter. I'm pretty sure the most common multimeters on the market are analog-to-digital converters built from field-effect transistors, which are at their heart voltage-measurement devices.

For a more exotic approach, you might like to read about the Kibble's "watt balance". The majority of Analog meters are based upon the D'Arsonoval meter movement. This is just a galvanometer, which causes deflection, due to current.

The D'Arsonoval meter movement works like an electric motor. Permanent poles and iron segments form a horseshoe magnet. A coil made from Manganin or Constsntin wire to make the meter temperature insensitive is formed around, but not attached to, a cylindrical iron core. Current is passed through the moving coil, which forms a magnetic field. This field interacts with the permanent magnets causing deflection. Stronger the current, the more deflection.