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Resistance and resistivity
Page 117
Chapter 10


Electrical resistance

There are two factors that affect the size of the current through a component:

1. The potential difference or voltage across the lamp ­ the greater the voltage, the
greater the current for a given component.

2. The resistance of the…

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The ohm is equivalent to `1 volt per ampere', 1 ohm = 1 V A 1

Determining resistance


In order to determine the resistance of a component we need to measure voltage across it and
current through it:

1. The ammeter is connected in series with the conductor, so that…

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Resistance = Gradient of graph



Ohm's Law

Ohm's law definition
For a metallic conductor at constant temperature, the current in the conductor is directly
proportional to the potential difference across its ends.

















There are some points we should notice about this graph of the light emitting diode:

1. There are…

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Resistance and temperature

In order for a component to obey Ohm's law, the temperature must remain the same. As
temperature increases the resistance increases and therefore the resistance is not constant and
so it doesn't obey ohms law.

A good example of this is the filament lamp. For low voltages,…

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And
Resistance is inversely proportional to cross section area
Therefore
Resistance = length / cross sectional area

Resistivity = (resistance x cross sectional area) / length




Summary


Resistance is defined as the ratio of voltage to current

Another term for voltage is potential difference

The ohm is the resistance of…

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