207 - Παραδείγματα ηλεκτρικών φορτίων

207 – Παραδείγματα ηλεκτρικών φορτίων και μαγνητισμού

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Γενικό Λύκειο Νυδριού Λευκάδος Γουρζής Στάθης – Φυσικός

Where do charges come from?

Matter is made up of atoms. + Proton (positive charge)

–

neutron (neutral)

+ + –

+ –

atom

– electron (negative charge)

nucleus

Electro-negativity Relative electro-negativity ranking for some common materials from electron donating materials (+, glass) to electron accepting materials (-, teflon)

+++++ ++++ +++ ++ + -----------

• • • • • • • • • • • •

Glass Human Hair Nylon Silk Fur Aluminum Paper Cotton Copper Rubber PVC Teflon

Where do charges come from?

When a balloon rubs a piece of wool... +

–

+

– – – – –

+ + wool

+

electrons are pulled from the wool to the balloon.

The balloon has more electrons than usual.

The balloon: – charged, The wool: +charged

Transferring Charge • Electroscopes are instruments that can be used to detect the presence of a charge.

Electricity - electrons moving through a metal wire.

Atomic Absorption

Static electricity

A Capacitor holds a charge on its plates.

semi-Conductor

Integrated circuit

There are many sources of electricity such as:

Fossil fuels: coal, oil and wood.

Electric Potential Energy • This spring has more SPE when it is compressed • Likewise, these charges will have more potential energy when they are pushed closer

Electric Potential vs Potential Energy • Which charge has more electric potential? • Which has more potential energy?

Potential Difference (voltage) • Why aren’t birds on power lines shocked?

• The Potential Difference between their feet is zero! (0 voltage)

The ion-electron equations can be re-written to show each step in the reaction:

Mg2+

Mg

+

2e

Cu2+

+

2e

Cu

Mg2+

+

2e

Mg

Benjamin Franklin, ca.1750 • Benjamin Franklin – single electrical fluid – Transfer of electrons – Positive and negative charges

• Atomic structure

Lightning Lightning occurs when the negatively-charged clouds interact with the positive charged ground

Lightning Lightning occurs when the negatively-charged clouds interact with the positive charged ground

II. Magnetic fields

II. Magnetic fields

The Earth is a magnet: It exerts magnetic forces and is surrounded by a magnetic field that is strongest near the North and South magnetic poles

Magnetism at Different Scales • Northern Lights

• Magnetic Bacteria