Physics General Physics II - PDF Free Download

Physics 21900 General Physics II Electricity, Magne/sm, Op/cs, and Modern Physics Review III: Chapter 21 28 Spring 2017 Semester Prof. Andreas Jung

Bubble/Cloud chamber

Announcement Final Exam Monday, May 1 st 8:00-10:00 am Room PHYS 203 Covers material from lectures 16-28: PropagaJon of light, refracjon and reflecjon Lenses and mirrors DiffracJon and interference ElectromagneJc waves, polarizajon Quantum opjcs, the Bohr model of hydrogen de Broglie waves Nuclear structure and decay Problems are designed more similar to the 1 st exam, i.e. not that depended on each other adjustment for 2 nd exam is sjll to come.

The Law of ReflecBon

RefracBon of Light Angles of incidence and transmission are measured with respect to the normal line which is perpendicular to the interface. Incident ray θ 1 θ Index of refracbon (n) 2 Experiment established a mathemajcal relajonship between the angle of incidence and the angle of transmission TransmiZed ray that depends on the parjcular medium.

Index of RefracBon The index of refracjon is a property of a parjcular medium. Indices of refracjon have been measured for many materials: The index of refracjon of vacuum is always n=1. The index of refracjon of any material is always n>1.

Origin of the RefracBve Index RefracJon is caused by the change in the speed at which light propagates in one material compared to the other. The index of refracjon (n) is the rajo of the speed of light in vacuum (c) to the speed of light in the material (v). n= c/v = 3.00 10 8 m/s/2.26 10 8 m/s =1.33

Snell s Law (1621)* θ 2 θ 1 n 2 n 1 n 1 sin θ 1 = n 2 sin θ 2 We use the convenjon where light propagates from medium 1 into medium 2. * First reported by Ibn Sahl, Baghdad 984 AD.

Total Internal ReflecBon Air, n 2 Water, n 1

Prisms Dispersion of Light The refracjve index of most materials depends on the color of light (wavelength). In general, n is larger for violet light and smaller for red light. n 1 sin θ i = n 2 (λ) sin θ r

InteracBon of Light with MaRer

Where is the Image Located?

Image FormaBon s s 1. A ray parallel to the principal o axis is refracted through i the focal point. 2. A ray through the center of the lens is not refracted. 3. A ray through the focal point is refracted parallel to the principal axis. An image is formed because light reflected from a point on the object is observed no mazer where the eye is posijoned. f

Sign ConvenBons are Important (Different text books may use different sign convenjons)

OpBcs Three ways to describe the properjes of light: Geometric opjcs Light travels in straight lines (rays) Wave opjcs Light is described by waves Quantum opjcs Light is described by parjcles (photons) that sajsfy the laws of quantum mechanics

Geometric OpBcs vs Wave OpBcs Water waves passing through a narrow opening Plane wave In both cases, the opening has a dimension comparable to the wavelength of the waves. Sound waves passing through an opening Plane wave ExpectaJon based on ray propagajon In both cases, the wave bends around the edges of the opening.

Young s Double Slit Experiment - 1803 Is this what happens? PredicJon based on the ray nature of light. (not to scale) W

ConstrucBve/DestrucBve Interference for two slits Waves that are in-phase give construcjve interference Waves completely out-of-phase give destrucjve interference.

Interference

Summary so far TWO KEY IDEAS Two ways to produce a phase difference between two waves: 1. One wave travels an extra distance 2. A reflecjon from an opjcally dense material produces a phase change of π upon reflecjon. (A phase change of π is the same as a path length difference of λ/2)

Where are the bright spots located? Spacing between slits is d.

Maxwell s EquaBons All known fundamental properjes of electricity and magnejsm are summarized by the equajons:

Changing B & E fields spread w/o any charges or currents

An electromagnebc wave

Example 3: The frequency of an EM wave is 4.5x10 14 Hz. The amplitude of the magnebc field is 6.0x10-4 Tesla.

Antennas are used to launch EM waves

ProperBes of ElectromagneBc Waves

Intensity of an EM Wave

PolarizaBon of Light PolarizaJon is a property of light that describes the orientajon of the E -field oscillajon in the wave.

ElectromagneBc waves Wavelength, λ, describes the color of light: We use the intensity (power per unit area) to describe the amount of light. We can talk about the power per unit wavelength to describe the amount of light of a parjcular color (the spectrum).

Blackbody RadiaBon If we increase the temperature, we nojce three things: 1. The total power output from the hole is now greater. 2. The intensity increases at all wavelengths 3. The posijon of the peak intensity shims towards smaller wavelengths.

Example The maximum power per wavelength of light from the Sun is at a wavelength of about 510 nm, which corresponds to yellow light. What is the surface temperature of the Sun? Wein s displacement law:

The ultraviolet catastrophe In the late 19 th century, no models could explain why the intensity dropped at small wavelengths. This problem became known as the ultraviolet catastrophe.

Planck s Hypothesis

Photoelectric Effect Long wavelengths (eg, red light) did not eject any electrons, independent of the intensity. Blue light did cause a current to flow The voltage needed to stop the current flow depended on the wavelength This measures the maximum kinejc energy of the electrons when ejected from the surface of the metal The current depended on the intensity

Review

Visible EM RadiaBon From Maxwell in the 1860s, we know that light is an EM wave. In 1888, Hertz showed that EM waves with long wavelengths could be launched and detected using transmizers and receivers (the forerunners of today s communicajon industry). But what about visible light? How is it generated? Consider a few sources of visible light: Sun Fire Oil lamp Heat radiajon (blackbody) Gas discharge tube

Hydrogen discharge tube

Bohr s model for light emission from H

Size of the hydrogen atom

Allowed energy levels for the H atom

Example

Energy of Electron orbits

What is the de Broglie wave length of a student of 75 kg running to lecture with 1 m/s?

Summary of Quantum Numbers Principal quantum number: Orbital angular momentum quantum number: MagneJc quantum number: Spin magnejc quantum number:

Pauli s Exclusion Principle

Atomic subshells from lowest to highest energy (approximate)

Mass/Energy RelaBonship

Nuclear Binding Energy

Nuclear Fission

Solar Energy The sun converts hydrogen to heavier elements through the process of nuclear fusion. The total energy released is 26.22 MeV. The first step is very slow which is why stars burn for billions of years Protons usually just bounce off each other and don t fuse to form deuterium.