derive the charge on an electron?
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The charge on electron was first measured by J.J. Thomson and two co-workers (J.S.E. Townsend and H.A. Wilson), starting in 1897. Each used a slightly different method. Townsend's work will be described as an example.
Townsend's work depended on the fact that drops of water will grow around ions in humid air. Under the influence of gravity, the drop would fall, accelerating until it hit a constant speed.
Several items were measured in this experiment.
1. the mass of a water droplet (actually the average mass of many)
2. the total electric charge carried on all the droplets (this was done by absorbing the water into an acid and measuring the charge picked up.)
3. the velocity of the droplet
4. the total mass of all water droplets (found by measuring the acid's increase in weight)
He determined the e/m ratio of the droplets (2 divided by 4), then multiplied by the mass of one droplet to get the value for e.
Thomson, Townsend, and Wilson each obtained roughly the same value for the charge on positive and negative ions. It was about 1 x 10¯19 coulombs. This work continued until about 1901 or 1902.
Townsend's work depended on the fact that drops of water will grow around ions in humid air. Under the influence of gravity, the drop would fall, accelerating until it hit a constant speed.
Several items were measured in this experiment.
1. the mass of a water droplet (actually the average mass of many)
2. the total electric charge carried on all the droplets (this was done by absorbing the water into an acid and measuring the charge picked up.)
3. the velocity of the droplet
4. the total mass of all water droplets (found by measuring the acid's increase in weight)
He determined the e/m ratio of the droplets (2 divided by 4), then multiplied by the mass of one droplet to get the value for e.
Thomson, Townsend, and Wilson each obtained roughly the same value for the charge on positive and negative ions. It was about 1 x 10¯19 coulombs. This work continued until about 1901 or 1902.
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The charge on electron is positive e-
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