Science

[parf]

What is the relative mass of an electron?

[Clanad]

Assuming the electron is at rest relative to the observer (me), it's mass is 9.10956 x 10-31 kilogram (kg) (for any electron since they are all the same)...
When an electron is accelerated to high speed, its mass increases because of relativistic effects. This increase is not significant until the speed of the particle, relative to the observer, becomes an appreciable fraction of the speed of light (c). If v is the speed of an electron in meters per second (m/s) and c is the speed of light (approximately 2.99792 x 108 m/s), then the mass of an electron in motion, me*, is:

me* = me / (1 - v2/c2)1/2 = 9.10956 x 10-31 / (1 - v2/c2)1/2 kg

(With partial thanks to Tech Target)

[jake-the-peg]

There may be some misunderstanding here.

Relative mass is sometimes a terminology used to compare the mass of subatomic particles to that of a proton or neutron.

Styrictly speaking this should be called the relative atomic mass

Precisely a relative mass of 1 is 1/12 the mass of a Carbon 12 nucleus.

This gives the electron a relative atomic mass of 1/1830 or 0.000546

http://www.wbateman.demon.co.uk/asa2sums/sum1. 1/sum1.1.htm

Clanad is referring to relatavistic mass.

I'm not clear exactly which one you want - if this is GCSE stuff then it's probably relative atomic mass

http://www.bbc.co.uk/schools/gcsebitesize/chem istry/classifyingmaterials/atomic_structure1re v1.shtml