H tension HW answers

I’ve marked your HW jotters and will hand them back during tomorrow’s lesson.

I’ll go over the main issues in class but many of you need to review the way you attempt tension questions; use a free body diagram and only use F=ma when you know the resultant force.  These two videos should help.

HW question 4 from mr mackenzie on Vimeo.

 

Higher HW Q5 from mr mackenzie on Vimeo.

particle accelerators

An electric field can be used to accelerate charged particles.

Conservation of energy tells us that

work done by the electric field = change in the particle’s kinetic energy

The speed of the particle can be determined if its charge and the accelerating voltage (potential difference) are known.  The notes attached to the end of this post will show how to perform the calculation.

These short video clips show how to draw electric field lines for point charges and parallel plates, with example calculations for the work done by electric fields and the final speed of charged particles in electric fields.

Q1(a) Electric fields lines around point charges from mr mackenzie on Vimeo.

Q1b – Electric field between parallel plates from mr mackenzie on Vimeo.

Q2 – Work done in moving a charged particle through a potential difference from mr mackenzie on Vimeo.

Q3 – Calculating the speed of a charged particle in an electric field from mr mackenzie on Vimeo.

quarks, leptons and antimatter

At the end of Our Dynamic Universe, we considered big things like stars, galaxies and the Universe itself.  Now the Particles and Waves unit brings us to particles so small we need groups of them just to make a single atom.  Is there a connection?


Why do we study particles? from mr mackenzie on Vimeo.
 

The Standard Model

An elementary (or fundamental) particle is a particle that is not built from other, smaller particles.  Until the start of the 20th century, scientists had believed that atoms were elementary particles.  However, the discovery of the electron (J.J. Thompson), proton (Rutherford), and neutron (Chadwick), together with Rutherford’s evidence for a heavy, positively charged nucleus at the centre of the atom suggested the atom was not an elementary particle after all.

Brian Cox explains in this video clip…

To go further, we have to introduce some particle physics vocabulary.

These new elementary particles are part of our Standard Model of how the building blocks of the universe interact with one another.  The particles that form “matter” are called fermions, after Enrico Fermi  (Fermi has an incredibly long list of things named after him).  The fermions are divided into two groups; quarks and leptons, as shown in the diagram below.

standard model


The Standard Model of Particle Physics. image: The University of Tokyo

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