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Another Unit for
Energy
In Electricity you can use
the kilowatt hour as a
convenient unit for large
energy values.
At the atomic scale we
need a new energy unit for
very small energy values ­
The electronvolt.

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The electronvolt
This is a non-SI unit of
energy based on the
Kinetic Energy gained by
an electron when it moves
through a potential
difference.

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The electronvolt
1 electronvolt is defined as
the charge on an electron
multiplied by a potential
difference of 1 volt.

Unit: eV
(1eV = 1.6x10-19J)

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Converting
IMPORTANT: You cannot
use eV values in any
equation. You must
practice converting energy
values between Joules and
electronvolts.
Remember this acronym:
D eV J M
(Pronounced "Devjem")

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D eV J M
D (eVJM)
i.e. to convert
electronvolts to Joules you
MULTIPLY the eV value by
1.6x10-19.

(DeVJ) M
i.e. to convert Joules to
electronvolts you DIVIDE
the Joule value by
1.6x10-19.

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Using eV
As a unit, electronvolts can
be used to express any
energy value for any
object or system ­ it's not
limited to just electrons.
(in practice it's only used
for energies on the atomic
scale)

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Test
Calculate the missing
values using "DeVJM"

electronvolts Joules
13.6 eV
3.2 x 10-18
25.0 keV
4.8 x 10-14
0.511 MeV
1.5 x 10-10
938.3 MeV

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Reminder
Mobile phones, PDAs,
digital cameras or any
other non-approved
electronic device are not
allowed in examination
rooms. Do NOT bring
them with you on the days
when you have public
examinations.

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