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