voltmeter
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A Volt meter is used to measure potential difference (a.k.a. voltage). Potential difference is measured in units called: Volts (V).
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Voltage is Current multiplied by Resistance. The formulas for calculating the resistance in parallel and series circuits are: Resistors in Series: R(total)=R1+R2+R3+... Resistors in Parallel: 1/(Rtotal)=(1/R1)+(1/R2)+... Current is a measure of Coulombs of charge per unit of time or I=C/t The current depends on the circuit, whether it has capacitors or resistors, and the exact layout. Current 'flows' through wires in much the same way that water flows through pipes, so if the current meets some resistance (a resistor), some of the current will go through the resistor, but the rest will go through any other available path (like in a parallel circuit).
You can compare 'potential' with height, and 'potential difference' with the difference in height.The height of an object depends upon from where you measure it. For example an object three-quarters of the way up a 1000 m mountain is +750 m from the base of the mountain, but -250 m from the top of the mountain. Note how we apply a positive or a negative sign to indicate whether we are measuring upwards or downwards.The same applies to potential. It's value depends upon from where it is measured. For example, two charged objects could have a potential of , say, +5 V with respect to earth (ground) and a potential of -15 V with respect to earth. But the potential difference between them will be +5 - (-15) = 20 V.Notice how, in the above example, we always show a positive or negative sign when we talk about potential, but we don't use these signs when we talk about a potential difference. Furthermore, it is important that we must ALWAYS specify the reference point when we describe potential -e.g. "What is the potential at point A, with respect to (say) earth?"Taking this further. It's important to know that the term 'voltage' means 'potential difference', and not'potential'! It would be quite wrong to say that the 'voltage of an object is (say) -200 V with respect to earth'. The correct expression would be the 'potential of an object is -200 V with respect to earth'.
Fill the graduated cylinder with water, and measure the volume. Now put the item in, measure the water's volume again, and take the difference