Writers: Edi Gonzalez
Chief Editor: Blake de Pastino
Consultant: Dr. Heiko Langner
Director/Editor: Nicholas Jenkins
Sound Designer: Michael Aranda
Graphics: Thought Cafe
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- why did Rutherford used only gold foil in his experiment? why he did not used any other element?(57 votes)
- as stated in video at3:24, how was J.J. Thomson able to calculate mass of the rays as told it was 1000 times lighter than hydrogen.(8 votes)
- The statement in the video is wrong.
In 1897, J. J. Thomson used an electric field (V) to accelerate electrons into a magnetic field (B).
The magnetic field deflected the electrons into circular paths of known radius (r).
He could then calculate the charge-to-mass ratio (e/m) of the electron.
e/m = 2V/(B²r²)
In 1906, Robert Millikan's famous oil drop experiment gave the charge on an electron.
Only then did it become possible to calculate the mass of an electron.(37 votes)
- I stumbled upon this link a while ago. Why isn't this incorporated into the western modern day chemistry we study?
- it isn't included into the present day chemistry of western culture because many of the western scientists did not believe that india was more advanced in the feild of science in ancient times than them also the early indian knowledge of sages was passed down verbally and therefore there was no written evidence for a long time
may be even before that time these things were known to indians but due to the absence of proper written evidence the western culture tends to credit ancient greek philosophers for most of the basic knowledge in the feild of science and maths.(12 votes)
- Why did Rutherford use a screen coated with zinc sulphide?(11 votes)
- Zinc sulphide gives a bright spot wherever a particle of appropriate size strikes it. This allows in counting. Read up on scintillations.(15 votes)
- in the video, at4:40, it is said that rutherford expected the rays to pass through straight. According to thomson's model, the electrons are embedded in a positive matrix. should he not expect all the rays to rebound?(9 votes)
- Even with the plum pudding model, an atom would be largely empty space so you would expect alpha particles to pass through unimpeded. Furthermore, with this model, even if an alpha particle did, by chance, encounter a proton it would be an isolated proton and no match for the heavier alpha particle. What Rutherford found is that the protons (neutrons had not yet been discovered) were all concentrated in one place giving a very dense nucleus able to repel or deflect the alpha particles.(7 votes)
- At5:12how does the bombardment of nitrogen on alpha particles create hydrogen ions?(3 votes)
- Nitrogen-14, when bombarded with high energy alpha particles, will form Oxygen-17 and release a proton. This is nuclear fusion.(11 votes)
Isn't electron 2000 times lighter than hydrogen? Why did he say that cathode ray is about 1000 times ligher than hydrogen? Did I miss something?(1 vote)
- Back then, in the late 19th and early 20th century, there were not so much sophisticated equipments to measure the quantities of so tiny a paticles. Also, JJ Thomson measured the values of e/m, but neither e nor m were determined. Milikan's oil drop experiment determined the value of e, and hence m was detemined. so, there is a bit of untrue info at3:26(4 votes)
- Do electrons orbit like planets (teacher test question)(1 vote)
- The structure and the movement of electrons might be a bit similar to that of Planets in Solar system, but the motion, energy and characteristics of electrons are quite different from planets. But of course, the way sun pulls the planets towards itself could be compared to nucleus pulling electrons towards itself. In both cases, Centrifugal and Centripetal forces are acting.(3 votes)
- If the plum pudding model states that the electrons are embedded in a cloud of positive charge, why did Rutherford expect the alpha rays to pass right through? Shouldn't he think that they will repel and the rays will reflect back?(1 vote)
- Not at all. The volume of the gold atom is about 10¹³ times the volume of its nucleus, so the density of the positive charge is extremely small.
It really was like shooting the α particles through a thin cloud.(4 votes)
- Thanks for the amazing video Khan Academy. Well, I've learnt that during the experiment the electricity should be passed in high voltage and in low pressure which in result show a good conductivity in the gases. Why ?(2 votes)
- During high pressure, in gases the density increases. Hence the electron density increases and therefore the conductivity is higher.(1 vote)