Exam 1 Next Tuesday Covers readings from Chapters 1-5 and S1. Two Essay questions 25 multiple choice questions. Allowed one sheet of notes (standard sized) with writing on one side only

Discussion Will the Moon still have phases? Explain.

Discussion What would happen to the Moon if its orbital period was less than the Earth’s day?

Newton and Kepler Newton’s laws of motion combined with Kepler’s laws led directly to the formulation of the universal law of gravity. Using Newton’s laws and the law a gravity you can derive Kepler’s laws of planetary motion. Planetary motion is thus just a special case of ordinary Newtonian motion.

The planets move in ellipses with the Sun at one focus. Conic section orbits are a natural outcome of the 1/d 2 nature of the gravitational force. Kepler’s 1 st law

A line drawn from the planet to the Sun sweeps out equal areas in equal intervals of time. Just another way of saying angular momentum is conserved which comes from Newton’s 2 nd law of motion. Kepler’s 2 nd law

Kepler’s 3 rd law The square of the sidereal period is proportional to the cube of the semimajor axis of the orbit: p 2 = a 3 Newton’s laws require:

The Scientific method at work Use the simplest model to explain the observations Refine the model, make it more complicated, only if new observations require Explain why the model works

Explanation vs. usefulness Kepler’s laws were adopted because they were useful for predicting planetary motions. Newton’s laws explained why Kepler’s laws worked in a broader context.

Discovery of Neptune Saturn and Uranus did not follow Kepler’s laws exactly Le Verrier and Adams use these deviations to predict the existence and position of Neptune which was observed in 1846

Gravity That one body may act upon another at a distance through a vacuum, … and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man who has … a competent faculty in thinking, can ever fall into it. Isaac Newton 1692

Light

The primary source of information we have about the solar system comes from the light received from space.

Does light travel instantaneously from one place to another? Galileo unsuccessfully tried to measure speed of light between two mountains using lanterns.

Speed of Light Olaus Romer – in 1676 noticed that the timing of eclipses of the moons of Jupiter was dependant on the relative positions of Jupiter and the Earth. The eclipse of a moon of Jupiter was 16.6 minutes later when Jupiter was near conjunction than when Jupiter was near opposition.

Discussion Why would the position of the Jupiter in the sky cause a change in the timing of the eclipses of the moons of Jupiter?

Romer’s Speed of Light Determination

Fizeau-Foulcoult Apparatus Light travels at a speed of 3.00 × 10 8 m/s

What is the Nature of Light? Light is a form of electromagnetic radiation, i.e. light is oscillating electric and magnetic fields. An oscillating electric field produces an oscillating magnetic field and an oscillating magnetic field produces an oscillating electric field.

Electric and Magnetic Waves

Water Waves

Frequency Wavelength Relation

Fields Electric fields cause charged particles to move. Magnetic fields cause magnets to move.

Electric Field Waves

Frequency and wavelength Because the speed of light is constant, for all observers and all frequencies, higher frequency electromagnetic waves have shorter wavelengths and lower frequency electromagnetic waves of longer wavelengths.

We see variations in wavelength or frequency as color White light contains all colors of the rainbow

The energy of electromagnetic waves. E = h  f = h  c/ The higher the frequency, or the smaller the wavelength, the higher the energy. h is a constant, f is the frequency is the wavelength, and c is the speed of light

The Electromagnetic Spectrum

Discussion In the movie Superman, the caped wonder claims to be able to tell the color of Lois Lane’s underwear with his X-ray vision. Is this possible, or did Superman rifle though her dresser drawers when she wasn’t home?

Light interacts with matter in four general ways 1.Emission 2.Absorption 3.Transmission 4.Reflection Come up with an everyday example of each.

Three types of spectra Continuous – emits all frequencies of colors of light Emission line – only specific frequencies are emitted. Absorption line – mostly a continuous spectrum with specific frequencies missing

Continuous, Absorption and Emission Spectra

Discussion What is light?

Discussion How can I create light with a magnet?

There are two types of emission Blackbody or thermal emission which produces a continuous spectrum, i.e. all colors of the rainbow. Line emission which produces only certain wavelengths of light.

Blackbody radiation In general the spectrum emitted by a hot object depends on the composition of the object. But there is a class of objects, called blackbodies because they appear black, that are perfect absorbers and perfect emitters. The spectrum of a blackbody depends only on its temperature.

Discussion It is fairly easy to see that a perfectly black object is a perfect absorber of light. But why is a perfect absorber also a perfect emitter? What do you think would happen if a perfect absorber were not a perfect emitter?

Discussion All objects emit thermal (blackbody) radiation. Why?

Atom

Temperature

Properties of thermal radiation 1)Blackbodies emit radiation at all frequencies. Thus, they emit a continuous spectrum, all the colors of the rainbow.

Blackbody Radiation

Properties of thermal radiation 2) Wien’s law – the temperature of the object is directly proportional to the frequency of maximum emission.

Discussion Why do you think the frequency of maximum emission increases with the temperature of the object?

Properties of thermal radiation 3) Stefan-Boltzmann law – the intensity of the emission is proportional to the 4 th power of the temperature.

Thermal Spectra

Infrared Image

Ionized hydrogen gas cloud

Discussion An excited electron will drop rapidly back down to ground state, emitting a photon. If the photon absorbed is the same wavelength as the photon that is emitted, why do we see dark absorption line features in the spectrum?