Category Electricity

        A voltmeter is an instrument that measures the voltage between two points in an electric circuit. It can be connected to a circuit by joining its positive and negative wires to where the voltage is. With such an arrangement, the instrument is said to be parallel to the electrical circuit.

       A voltmeter can be used for many purposes. For instance, to check whether there is any more electricity left in a battery.

       In an analogue voltmeter, the pointer indicates the number of volts. In a digital voltmeter, the reading will be displayed digitally. There are also voltmeters that can be mounted on a transformer, and other huge devices.

       Yet another variety is a voltmeter that uses amplifiers in them. Such meters can measure very small, or tiny voltages of microvolts, or even less.

         A galvanometer is a tool that measures the flow of electric charges through a wire. This basic device consists of a coil placed in a magnetic field. It can be used for detecting and comparing small electric currents.

        The ideas of galvanometers are known to have developed from an observation made by Hans Orsted in 1820. He had found out that the needle of a magnetic compass deflects near a wire that has electric current passing through it. But it was Johann Schweigger who built the first sensitive galvanometer in the same year. Galvanometers, since then, came to commercial use.

        A galvanometer can be used as an ammeter, as well as a voltmeter. By connecting a shunt in parallel to the coil, it acts an ammeter, and if the shunt is connected in series with the galvanometer coil, it becomes a voltmeter. 

          A multimeter is an instrument that measures the voltage, current, and resistance of an electrical device. Also known as a VOM (Volt-Ohm-Milliammeter), they are very useful in providing field measurements or detecting faults with accuracy.

          The first multimeter was invented by Donald Macadie, a British post office engineer who was unhappy with the need to carry separate instruments needed for the maintenance of telecommunication circuits. His invention was the instrument that could measure amperes, volts and ohms, and was named the avometer.

          The device is commonly used by electricians and other experts to troubleshoot problems on appliances, motors, circuits, power supplies and wiring systems. They could use the device on batteries, switches, power sources etc for measuring or diagnosing.

            Multimeters can be analogue or digital. Analogue multimeters are cheaper, but their readings are not as accurate as the digital meters. Recent digital multimeters are advanced enough to measure extremely tiny differences or fluctuations. 

          Direct current, as we know, is the flow of electric charge in just one direction. The history of electric power records that the first commercial transmission was made possible using direct current.

           This was perhaps because DC was the only option then. But as time passed, it proved to be insufficient. Because with direct current, voltage couldn’t be changed easily. What made it worse was that, different classes of loads, for instance, lighting, motors, and railway systems etc, required different voltages. So for this, there had to be different generators and circuits.

           However, in the course of time, alternating current took over and electric transmission became easier than before. We have seen that this type of current can reverse its direction, and serve better than DC. In 1884, the first long distance AC line was built in Italy, proving that AC was better for long distance transmission.

           As years passed, newer technologies were introduced. By the mid 1950s, an advanced type of direct current transmission was developed, and was named the high voltage direct current transmission. Today, it is the alternate and the most acceptable option for long distance, bulk transmission of electric power, especially between countries.

        Alternating current, as we saw, periodically reverses its direction, whereas direct current (DC) flows always in the same direction. The amount of current can change in a DC circuit, but their general direction remains the same.

         Perhaps the best and the simplest example of direct current is a battery. Take a look at one of them in your house. You can spot two terminals – +ve and -ve. If a wire is connected to these two terminals, it will cause a flow of electrons resulting in the production of electricity.

         Other than this, direct current is used as power supply for electronic systems and also for charging batteries. DC is thus used for many purposes, though for smaller and less complicated ones, unlike AC power. But direct current can be converted to alternating current through devices like an inverter or a motor-generator set.

         Direct current is produced by various sources such as solar cells, dynamos etc. It mainly flows in good conductors such as wire, but can also flow through semiconductors, insulators and even vacuum.

         Electric current in DC is measured in ampere and voltage in volts. 

        Electric current moves often like a water stream. The only difference here is that electric charges do not always move in the same direction. When they do, it is called Direct Current or DC.

        On the other hand, AC or Alternating Current, as the name suggests, occurs when charge carriers in a conductor, or semi conductor, reverse their direction of movement in a periodic manner.

        With AC, it is possible to run many types of electrical equipment like generators, motors, power distribution systems etc. and also kitchen appliances, TVs, electric lamps etc. Hence, for almost all high power applications, it is a global trend to use AC instead of DC because of its higher efficiency. Besides these advantages over DC, AC power is believed to be less expensive. One can also use high voltages with small currents to reduce losses, with AC power.

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