The flow of charged particles measured in amperes. The rate of flow of charge / amount of charge passing through a given point per second. I = Q/t
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Electric Charge
Measured in coulombs, a derived unit named after a French physicist, it is defined as the electric charge flowing past a point in one second when there is an electric current of one ampere. 1C is equivalent to 1As (Ampere second)
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Charge of a proton
1.6x10E-19 C
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Charge of an electron
-1.6x10E-19 C
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Charge of a Copper(2+) ion
3.2x10E-19 C
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Charge of a Sodium(+) ion
1.6x10E-19 C
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Charge of a Chloride(-) ion
-1.6x10E-19 C
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Ions
Ions are relative charges that are measured against the constant e. e = 1.6x10E-19 C. A proton has +1e, an electron has -1e.
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Net charge
The charge of an object results from either a gain or loss of electrons by the object. The net charge of an object is given by Q = +- ne, where n is the number of electrons.
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The charge of an object is ...
The charge of an object is quantised. This means that charge can only take specific values - these being multiples of e.
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Millikan's experiment / The oil-drop experiment
The analysis of the motion of electrically charged oil droplets between two oppositely charged parallel plates. The oil droplets falling experience gravitational force, air resistance and upthrust. It was held upward by the attractive electrostatic f
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The structure of metal can be thought of as ...
a regular crystal structure/lattice of positive electrons surrounded by a number of free/delocalised electrons. The positive ions do not move, but do vibrate increasingly as temperature of the metal increases.increases.
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A larger current may be due to:
A greater number of electrons moving past a given point each second; the same number of electrons moving faster through the metal.
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Conventional current
Defined long before the electron, the current from a positive terminal to a negative one. The direction of all electric current is still treated like this, despite the direction of moment of charge carriers (- to +).
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Electrolytes
Liquids that can carry an electric current are called electrolytes. Not a flow of electrons, rather a flow of ions. All electrolytes are either molten ionic compounds or ionic solutions, like salt water.
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Electrolysis
If a positive electrode (anode) and a negative electrode (cathode) are placed in a solution, ions are attracted to them. For example, Na(+) ions move towards the cathode, Cl(-) ions move towards the anode. This is a flow of charge/an electric current
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Measuring electric current
An ammeter is used to measure the electric current at any point in a circuit. They should have the lowest possible resistance such that they do not affect the current - the ideal ammeter has zero resistance, and no effect on the current.
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Conservation of charge
The electric charge can neither be created nor destroyed. The total amount of electric charge in our universe is constant.
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Kirchoff's first law
Any point in an electrical circuit, the sum of currents into that point is equal to the sum of currents out of that point. Written as ΣI(in) = ΣI(out)
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Number density
The number of delocalised electrons per cubic meter of material. The greater the number density, the greater the electrical conductor. Typical conductors are 10E28 mE-3, semiconductors 10E17 mE-3.
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Semiconductors
Much lower number density than metals, so to carry the same current electrons must move much faster, increasing the temperature of the semiconductor. For example, computer chips use semiconductors, with processors made of silicon.
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A new equation of electric current
I = nAve = Number density x cross-sectional Area x Elementary charge x mean drift Velocity.
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The effect of changing cross-sectional area
If the c-sa of a wire changes, so must the drift velocity. The narrower the wire, the greater the drift velocity must be in order for the current to be the same.
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Other cards in this set
Card 2
Front
Measured in coulombs, a derived unit named after a French physicist, it is defined as the electric charge flowing past a point in one second when there is an electric current of one ampere. 1C is equivalent to 1As (Ampere second)
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