Ammeter:A device calibrated in amperes and used to measure the intensity of an electric current. An ammeter must always be installed in series to measure the current. +- A The current ( I ) is measured in amperes (A). Analogy to understand the ammeter: Now, imagine a river stream encounter a paddle wheel. The wheel is the ammeter and water is electric current.
An analogy: Let’s imagine a ball falling from different levels. Height difference or potential difference is low. Height difference or potential difference is high.
Voltmeter:A device equipped with two terminals that indicates the potential difference (voltage) between these two points.. A voltmeter must always be installed in parallel to measure the potential difference. It measures energy in volts (V). Voltage:also termed potential difference which is a quantity related to the amount of energy that would be required to move an object from one place to another against various types of forces. +- V e-e- BA An amount of energy is needed to move the electron from point A to point B. The difference in energy between A and B is called voltage.
+- A V IV AmpVolt 0.0 1.0 2.0 3.0 4.0 5.0 0.0 2.0 4.0 6.0 8.0 10.0 V or U (V) I (A) 1 2 3 4 5 6 7 8 9 4 6 8 10 12 14
Calculating the slope of V vs. I : Resistance Current is a function of voltage: I = f (V) Slope= ΔV / Δ I = 4.0 V – 1.0 V / 8.0 A – 2.0 A = 3 V / 6 A = 0.5 Ω R= ΔV / Δ I R: Resistance (Ω) Δ I : Current (A) ΔV: Voltage (V) Hence: R = V / I V R I I (A) U (V) 1 2 3 4 5 6 7 8 1 2 3 4 5 6 R = Δ V = y 2 – y 1 Δ I x 2 – x 1
Commonly used symbols in electric circuits: +- Battery (Cell) Light bulb Crossing wire with no contactCrossing wire with contact SwitchPush button switch Resistance A V Ammeter Voltmeter Power source +-