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RECAP

The Coulomb Force (fundamental force)

Voltage Ohms law

Resistance

Power

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Charge

Elementary charge e = 1.602 10 C

charge Q2distance r

charge Q1

Force between charges:

vacuum permittivity 8.854 10

Current: how many electrons are flowing by per time unit.

1

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Voltage

Current is driven by a voltage difference between two

points, i.e. a voltage difference tries to drive electrons to

the lower voltage point in order to eliminate thedifference.

Voltage (potential difference) is measured in Volt = Joule /

Coulomb, this is how much work each electron can

perform.The higher the voltage the harder are the electrons

pushed away from the higher voltage point. (like a

waterfall)

Voltage is relative by nature. Voltage makes only sensewhen compared/measured to a reference point. One

single point does not have a defined voltage.

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Ohms law

A voltage difference U (Volt) between two points causes a current I

to flow.

It is found that current is proportional to the voltage.

The (inverse) constant of proportionality is called the resistance R.

1

1

1A 1000 1

1000

1

1 1M

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Resistance of a regular shaped conductor

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Power

=

Voltage U

Resistor R

Current I

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Practical implementation

of resistors

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WIRE-WOUND RESISTORS (1)

Power dissipation: 5W 500W, resistance: typical < 1k

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WIRE-WOUND RESISTORS (2)

Power dissipation: 4W 17W, resistance: typical < 22k

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STANDARD LEADED CARBON OR METAL FILM RESISTORS

Power dissipation: 0.25W-3W, resistance: ~0.01 ~1G

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arbon Resistor Metal Film Resistors

+ cheap

+ can withstand higher

voltage

+ higher precision

+ less sensitive to changes in

temperature

+ lower noise

- larger tolerances

- higher noise floor

- more prone to aging

- a bit more expensive

(although the difference

flattens out)

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SURFACE MOUNTED DEVICE (SMD) RESISTORS

3mm

Power dissipation: 0.25W-3W, resistance: ~0.01 ~1G

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SURFACE MOUNTED DEVICE (SMD) RESISTORS

Power dissipation: 0.0625W-2W, resistance: 0 ~1T

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APPLICATION OF TEMPERATURE

COEFFICIENT

Temperature measurement

Some materials, e.g. platinum, have linear temperaturedependency

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Resistance vs. Temperature Pt100 element

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Reference: Lee, R. C, Dougherty, W., Electrical Injury:,

IEEE Trans. Dielectrics and Electrical Insulation, Vol. 10,No. 5, 2003

ELECTRIC SHOCK HAZARDS