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Module 1: Electric Current

Spread 1: Electric Current and Charge:

Charge = Current x Time. Q=IT.

One coulomb is the total charge supplied by a current of one amp, in a time of one second. 1C = 1A
X 1s.

The charge on a single electron is 1.6x10-19.

Electric Current…

Page 2

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Conventional Current: A model that describes movement of charge in a wire. Conventional
current travels from the positive terminal of a battery to the negative terminal.

Kirchoff's First Law: The sum of the current entering a junction is the same as the current leaving
the junction. Charge is conserved.

Page 3

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Electron Drift Velocity: The average velocity of an electron as it travels through a wire, due to a

Conductor ­ Material with a high number density of conduction electrons. Therefore, conductors
must have low resistance, to allow electrons to flow.

A Semi-Conductor ­ A material with lower conduction electrons…

Page 4

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Key Definitions:

Electromotive Force: E.m.f is the energy transferred per unit charge, when one type of energy is
converted into electrical energy. It is the energy per charge that is added to the circuit.

Electromotive Force = Electrical Energy Transferred/Charge.

Each cell above is 1.5V. Since the negative terminal of…

Page 5

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Potential Difference: p.d. is the electrical energy transferred per unit charge, when electrical
energy is converted into another form of energy. The potential difference is also the difference in
energy per unit charge that enters a component, and the energy per unit charge that leaves it.

The reading on a…

Page 6

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Ohm's Law: The current through a conductor is proportional to the potential difference across it,
provided physical conditions, such as temperature, remain constant.

Resistance: Resistance is basically opposition to flow of charge. R = V/ I. The definition of resistance is the
potential difference across a component / current flowing…

Page 7

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The graph is a curve for a filament lamp. Doubling the voltage does not however, produce double
the current. The value of V/I rises as I increases. As the current increases, the filament gets hotter;
this increases the resistance. The electrons in the filament of the lamp vibrate more and…

Page 8

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They are being used increasingly more for light sources as a substitute to filament bulbs.
One can be used as the `on' indicator on a TV; 100 can be used in a traffic light.
They emit strong sources of light.
They switch on instantly.
Very robust and versatile.
Operate on…

Page 9

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Spread 5&6: Resistivity:

Key Definitions:

Resistivity = Resistance x Cross-Sectional Area/ Length of a Wire. Unit is ohm metres.

Factors that Affect Resistance of a Wire:
Length: A longer wire has more resistance, as the path for electrons is increased, thus collisions
occur more often.
Area: A thin wire has…

Page 10

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Key Definitions:

Power: Power is the rate at which energy is transferred, measured in watts.

Fuse: These are devices introduced into circuits to protect the wiring from excessive currents.
These high currents cause wires to get hot, damaging them, and could result in fires. When a fuse
is subjected to…


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