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