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Module 4 - Chapter 9 - Energy, Power and resistance I - Coggle Diagram
Module 4 - Chapter 9 - Energy, Power and resistance I
Potential difference
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PD across a filament lamp is a result of electrial energy being transferred into heat and light as charge carriers move through the lamp
High pds are dangerous because charge carriers can transfer large amounts of energy through conductors, and sometimes even insulators
The Volt
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One volt is the pd across a component when 1J of energy is transferred per unit charge passing through the component
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Voltemeter
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An ideal voltemeter would have an infinite resistance so that no current passes through it, but in reality this isnt possible
The energy gained per unit charge by particles away from the electron, energy is transferrred from electrical to another form
Electromotvie force
pd is used to describe when work is done by the charge carriers, which lose energy as they pass through the component
emf is used to describe when work is done to the charge carriers, whcih gain energy as they pass through a component like a cell, battery or powerpack
Greater EMFs means more energy per coulomb hs been transferred into electrical energy (often from chemical)
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Energy gained per unit charge by partices passing through the supply, energy is transferred to electrical
Electron gun
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How does it work
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Some gain enough kinetic energy to escpae from the surface of the metal, this is called thermionic emissions - emission of electrons through the action of heat
If the heat filament is placed in a vacuum and there is a high pd applied between the filament and the anode (the filamen acts as the cathode) the electrons accelerate towards the anode
The anode has a small hole in it, and elctrons in line with the hole pass through it, creating a beam of electrons
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The work done to accelerate the electron is the charge of the electron X the pd between the filament and the anode
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Resistance
It takes energy to push electrons through a component, the higher the resistance, the more energy it takes
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Ohm
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Ohm's law
For a metallic conductor kept at constant temperature, the current in the wire is directly proportional to the pd across its end
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IV Characteristics
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Collecting data
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Its impoortant to check whether the component behaves in the same way if the current through it is in the opposite direction
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Resistors
Fixed resistros are designed to ensure their resistance is constant regardless of changes in temperature
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Filament lamps
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The filament lamp doesn't obey ohm's law, its a non-ohmic component
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As the Pd across the filament increases, so does the resistance
Reasons
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Increase in current mean increase is rate of flow of charge through the filamet so more electrons pass through it per second
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When electrons collide with ions, they transfer energy to the ions, causing ions to evapourate more, causing an increase in temperature
Diode
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In one direction, the diode doesn't conduct electricty
In the other direction as the Pd increases, the resistance drops sharply