Phy107Lect14_6per

# Phy107Lect14_6per - From Last Time Coulomb force between...

This preview shows pages 1–3. Sign up to view the full content.

1 Fri. Oct 8 Phy107 Lecture 14 From Last Time… • Coulomb force between charged particles – Same form as gravitational force • Electric field lines: path followed by charged particle • Electric current: flow of charged particles • Electrostatic potential: Measured in volts. Analogous to gravitational potential. • Magnetic field: arises from electric currents (moving charges) also results in force on an electric current • Faraday effect: changing magnetic field induces electric current Magnetic field from induced currents opposes change in applied field Fri. Oct 8 Phy107 Lecture 14 James Clerk Maxwell Electricity and magnetism were originally thought to be unrelated in 1865, James Clerk Maxwell provided a mathematical theory that showed a close relationship between all electric and magnetic phenomena Fri. Oct 8 Phy107 Lecture 14 Maxwell’s Starting Points Electric field lines originate on positive charges and terminate on negative charges (Gauss’s law for E) Magnetic field lines always form closed loops – they do not begin or end anywhere (Gauss’s law for B) A varying magnetic field induces an emf and hence an electric field (Faraday’s Law) Magnetic fields are generated by moving charges or currents (Ampère’s Law) Fri. Oct 8 Phy107 Lecture 14 Maxwell’s Predictions Maxwell used these starting points and a corresponding mathematical framework to prove that electric and magnetic fields play symmetric roles in nature He hypothesized that a changing electric field would produce a magnetic field Maxwell calculated the speed of light to be 3x10 8 m/s He concluded that visible light and all other electromagnetic waves consist of fluctuating electric and magnetic fields, with each varying field inducing the other Fri. Oct 8 Phy107 Lecture 14 Hertz’s Confirmation of Maxwell’s Predictions • Heinrich Hertz was the first to generate and detect electromagnetic waves in a laboratory setting Fri. Oct 8 Phy107 Lecture 14 Hertz’s Experimental Apparatus • An induction coil is connected to two large spheres forming a capacitor • Oscillations are initiated by short voltage pulses • The inductor and capacitor form the transmitter

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

View Full Document
2 Fri. Oct 8 Phy107 Lecture 14 Hertz Transmitter Hertz's radio wave generator (transmitter). The free standing structure on the right was a two meter high reflector with a spark gap and short dipole antenna at its focal point. The apparatus on the table was an induction coil to generate a high voltage spark at the gap. Figure 1 diagrams adapted from "Electric Waves", by Heinrich Hertz,MacMillan &Co. (1900) http://www.newscotland1398.net/nfl d1901/marconi-nfld.html Fri. Oct 8 Phy107 Lecture 14 Hertz Trans & reciever Magnified view of the spark gap and dipole transmitting ("feed") antenna at the focal point of the reflector. The high voltage spark jumped the gap between the spherical electrodes. The electrical
This is the end of the preview. Sign up to access the rest of the document.

## Phy107Lect14_6per - From Last Time Coulomb force between...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online