1. B. J.J. Thomson’s determined that charge and mass of electrons
QUESTION:
Which of these is true? A. Dalton assumed that atoms are made up of electrons, protons, and neutrons
B. J.J. Thomson’s determined that charge and mass of electrons
C. In Rutherford’s alpha scattering experiment, all of the alpha particles passed through the gold foil.
D. The alpha particles used in Rutherford’s experiment are positively charged particles.
Dalton assumed structureless spheres
Thomson: charge-to-mass ratio; Millikan determined charge
SCRIPT:
Which of these is true? A. Dalton assumed that atoms are made up of electrons, protons, and neutrons
B. J.J. Thomson’s determined that charge and mass of electrons
C. In Rutherford’s alpha scattering experiment, all of the alpha particles passed through the gold foil.
D. The alpha particles used in Rutherford’s experiment are positively charged particles.
PAUSE
Choice A is false. Dalton assumed that atoms are structureless spheres. It was J.J. Thomson’s cathode ray tube experiments that led to the conclusion that all atoms have electrons.
Choice B is false. J.J. Thomson’s experiment determined the charge-to-mass ratio.
CLICK Because the particles ejected from the cathode didn’t depend on the material used for the cathode, it was concluded that whatever particles were ejected from the cathode must be present in all atoms. The way the cathode rays are deflected by application of electric and magnetic fields suggested that the particles were negatively charged.
The charge of the electron was determined in Millikan’s oil drop experiment.
CALLOUT “Millikan determined charge of electron”
Choice C is false. Most, not all, of the alpha particles passed through.
CROSS OUT “all”
CALLOUT “most”
The striking result of Rutherford’s experiment is the backscattering of small number of alpha particles. This led to the notion that the mass of the atom is concentrated in a very tiny nucleus.
Choice D is true. Alpha particles are positively charged. In fact, each one consists of a 2 protons and 2 neutrons --- essentially a helium atom that has been stripped of its electrons. The backscattering of alpha particles suggested that the nuclei in the gold atoms are positively charged,,… since like charges repel.
CLICK
CLICK PAUSE END RECORDING
MOST, not ALL

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08