{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

l9 - Electrostatics and gravity Forces q and m The electron...

Info icon This preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
Forces: q and m The electron Plum pudding Electron charge Radioactivity Rutherford Thomson scattering Rutherford scattering Experimental confirmation Closest approach Electrostatics and gravity Recall electrostatic force: F = 1 4 πǫ 0 q 1 q 2 r 2 with ǫ 0 = 8 . 85 × 10 - 12 (mks units). Recall gravitational force: F = G m 1 m 2 r 2 with G = 6 . 67 × 10 - 11 (mks units). Ratio is 4 πǫ 0 G m 1 m 2 q 1 q 2 . Two protons: 4 πǫ 0 G m 1 m 2 q 1 q 2 = 4 πǫ 0 G ( 1 . 7 × 10 - 27 ) 2 ( 1 . 6 × 10 - 19 ) 2 = 8 . 1 × 10 - 37 Two electrons: 4 πǫ 0 G m 1 m 2 q 1 q 2 = 4 πǫ 0 G ( 9 . 1 × 10 - 31 ) 2 ( 1 . 6 × 10 - 19 ) 2 = 2 . 4 × 10 - 43 Gravity is a wimp! Most things must be electrostatically neutral.
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Forces: q and m The electron Plum pudding Electron charge Radioactivity Rutherford Thomson scattering Rutherford scattering Experimental confirmation Closest approach The discovery of the electron The American Institute for Physics has a good web site on this. Remember that much was swirling about with cathode ray tubes: first the discovery of X rays, then the discovery of electrons, then the photoelectric effect, all within a decade. Cathode rays: drawn from regular matter (the cathode). Are they particles? Constituents of atoms? Do they have some elementary charge? J.J. Thomson, director of the Canvendish Lab at Cambridge, thought so, but wanted to prove this. J.J. Thomson (1856–1940; Nobel Prize 1906)
Image of page 2
Forces: q and m The electron Plum pudding Electron charge Radioactivity Rutherford Thomson scattering Rutherford scattering Experimental confirmation Closest approach Thomson’s experiments 1. cathode rays carry negative charge (electrometer). 2. with good enough vacuum, electric field deflects cathode rays 3. use an accelerating voltage to give corpuscles with the same charge the same velocity qV x = ( 1 / 2 ) mv 2 or v = radicalbig 2 qV x / m
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Forces: q and m The electron Plum pudding Electron charge Radioactivity Rutherford Thomson scattering Rutherford scattering Experimental confirmation Closest approach Magnetic field alone Thomson’s third experiment with a magnetic field alone: m v 2 r = qvB q m = v rB q m = radicalbig 2 qV x / m rB = radicalbigg q m 2 V x rB giving q m = 2 V x r 2 B 2 (1) so I’m mystified why Thomson didn’t consider this sufficient! Note that this ignores relativity; it would have us start out with γ mv 2 / r = qvB (1909).
Image of page 4
Forces: q and m The electron Plum pudding Electron charge Radioactivity Rutherford Thomson scattering Rutherford scattering Experimental confirmation Closest approach Electric field alone Acceleration due to voltage V y over plate separation d : a y = qE / m = qV y / ( md ) Velocity in ˆ y changes from 0 to v y = a y · Δ t = qV y md · v x (2) Recall velocity in ˆ x direction: v x = radicalbig 2 qV x / m Angle upon leaving electric field region: θ tan θ = v y v x = qV y md v x 1 v x = q m V y dv 2 x (3) = qV y md m 2 qV x = lV y 2 dV x which tells us nothing about q or m .
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Forces: q and m The electron Plum pudding Electron charge Radioactivity Rutherford Thomson scattering Rutherford scattering Experimental confirmation
Image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern