Measuring The Charge On The Electron Flashcards
Who determined the size of the charge on the electron?
Robert Millikan
What did Robert Millikan determine?
The size/magnitude of the charge on the electron
Describe the apparatus Robert Millikan used.
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A small box
A microscope at one vertical end
A dropper with oil at the other vertical end
Two metal plates lying horizontally, one at the top of the box and the other at the bottom
A positive charge on the top plate
A negative charge on the bottom plate
The air between the plates is ionised
What experiment did Millikan carry out?
He sprayed tiny droplets of oil between two charged particles
What did Millikan do to the air between the plates?
He ionised the air using X-rays
How did Millikan ionise the air?
With X-rays
What happened when Millikan ionised the air between the plates?
The molecules in the air lost electrons and formed ions
What happened as the oil droplets fell through the air?
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They picked up electrons (in the air due to the ionisation of the molecules with X-rays)
This caused the oil droplets to become negatively charged
What did Millikan use to focus on a particular oil droplet as it fell through the air?
A microscope
Why did Millikan need a microscope?
To focus on a particular oil droplet as it fell through the air
What did Millikan do once he had focused on an oil droplet?
He placed a positive charge on the top plate
What did Millikan observe when he placed a positive charge on the top plate?
He observed that the negatively charged oil droplet was attracted up towards the positive plate
What did Millikan do once the oil droplet was attracted up towards the positive plate?
He carefully adjusted the charge on the plate until the oil droplet was stationary i.e. suspended in mid-air
What was Millikan able to calculate from his results?
He was able to calculate the size of the charge on the electron and the mass of the electron (using Thompson’s results)
From Millikan’s research, how can the electron be described?
As a negatively charged particle of very small mass
