Post on 15-Feb-2016
description
Power source Any electrical appliance or
gadget
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.
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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.
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V e-
B AAn 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.
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A
V
I VAmp Volt
0.01.02.03.04.05.0
0.02.04.06.08.010.0
V or U (V)
I (A) 1 2 3 4 5 6 7 8 9
4 6 8101214
Calculating the slope of V vs. I : Resistance
Current is a function of voltage: I = f (V)
Slope = ΔV / ΔI
= 4.0 V – 1.0 V / 8.0 A – 2.0 A
= 3 V / 6 A
= 0.5 Ω
R = ΔV / ΔI
R: Resistance (Ω)
ΔI: Current (A)
ΔV: Voltage (V)
Hence:R = V / I V
R I
I (A)
U (V)
1 2 3 4 5 6 7 8
123
456
R = ΔV = y2 – y1
ΔI x2 – x1
Ammeter Voltmeter
Resistors
Commonly used symbols in electric circuits:
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Battery (Cell) Light bulb
Crossing wire with no contactCrossing wire with contact
Switch Push button switchResistance
A
V
Ammeter
Voltmeter
Power source
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ITotal = I1+ I2+ I3
VTotal = V1+ V2+ V3