Transcript Review for Exam I PHYS 1050

Review for Exam I
Chapters 1, 2, 3,4
PHYS 1050
May, 2002
Purpose
• This document is a study guide,
NOT a comprehensive list of all topics
included on the exam.
• The exam will cover material from both
the text and class notes.
Equations and Constants
• diameter/(2 x distance) = angular diameter/360o
• small-angle formula:
diameter = distance x (angular diameter/ 57.3o)
• F = ma
• Fgrav = Gm1m2/r2
• P2 = a3
• speed of wave = wavelength x frequency
• period = 1/frequency
• energy of wave proportional to frequency (or 1/wavelength)
• circumference of circle = 2  x radius
• area of circle =  r2
• astronomical unit = 1 AU = 150 x 106 km =
average distance from Earth to Sun
• speed of light = 300,000 km/sec
• light year = 1 LY = distance light travels in one year
• distance = speed x time
Definitions and Facts
•Age of the universe: ~ 12-17 billion years old
•Measuring distances
– parallax
– triangulation
•angles, baseline
– angular measurement
•Stars and constellations
– Polaris is “North Star”, marks the position in the sky
of Earth’s rotation axis.
– The “Big Dipper” is located in Ursa Major.
– Orion is a prominent constellation in the winter sky.
– Sirius is the brightest star in the sky.
•Celestial Sphere
– North celestial pole, celestial equator, meridian
– ecliptic, zodiac, equinoxes, solstices
– right ascension, declination
– altitude, azimuth, horizon, zenith
• Motion of the Earth
– rotation
•cause of day/night
•from WEST to EAST which causes objects to
rise in EAST and set in WEST
•describe daily motion of stars, Sun, and Moon
across sky at different latitudes
– orbital motion
•seasonal variation of constellations
– seasons
•rotational axis tilted at 23.5o to ecliptic
•seasonal variation of Sun’s rising/setting/noontime position
• Motion of the Moon
– orbital motion
• in eastward direction around Earth with
angular speed of 0.5o per hour
• lunar phases
– new, full, first quarter, last quarter, gibbous
and crescent (waxing/waning)
– relationship between lunar phase and
rising/setting time
– rotation
• rotates once per orbit about Earth:
synchronous rotation
– always see same face of Moon from Earth
o
The Sky from Denton: 33.5 N
• North Celestial Pole is 33.5o above northern
horizon.
• Celestial Equator is 56.5o above southern horizon.
• Circumpolar stars lie within 33.5o of North
Celestial Pole.
• Rising & Setting stars are visible from 33.5o away
from South Celestial Pole.
• Stars within 33.5o of South Celestial Pole are never
visible from Denton.
The Earth’s Rotation
• The Earth's west to east rotation causes the celestial sphere to
appear to rotate from east to west in 24 hours.
• LOOKING SOUTH
– The Sun, Moon, planets, and stars appear to rise in the east,
cross the meridian due south, and set toward the west.
– Celestial objects are said to transit when the cross the
celestial meridian in the southern sky. This is when they are
highest in the sky.
• LOOKING NORTH
– The stars appear to circle around the North Celestial Pole
(near Polaris) once in 24 hours.
– Stars within the angle of the observer's latitude away from
the North Celestial Pole never rise or set. They are always
above the horizon (circumpolar stars).
The Effects of Precession
• Causes the pole star to change.
– Thuban (in Draco) was the pole star in 3,000 B.C..
– Polaris (in Ursa Minor) is the pole star now.
– Vega (in Lyra) will be the pole star in 14,000 A.D.
• Causes intersection point of ecliptic and
celestial equator to shift.
– "Age of Aries" occurred 2,000 years ago.
– "Age of Pisces" is now.
– "Age of Aquarius" will begin about 400 years from now.
The Earth’s Orbital Motion
• The Earth’s orbital motion causes
– the apparent eastward motion of the Sun along the ecliptic
of about 1o per day.
– the annual motion of the Sun through the 13 zodiac
constellations.
– the seasonal visibility of stars and constellations.
• The tilt of Earth’s rotation axis by 23.5o causes
– tilt of the ecliptic with respect to the celestial equator.
– the Sun's declination to change during the year.
– seasonal variations in the altitude of the midday Sun,
length of day & night, and rising & setting directions of the
Sun.
Eclipses
• The Moon's orbit is inclined about 5o to the ecliptic.
That's why there are not eclipses every month.
• In order for an eclipse to occur, the Earth, Moon, and
Sun must be nearly perfectly aligned.
• All eclipses occur when the Moon crosses the ecliptic.
– Solar eclipses are possible only at the New Moon phase,
when the Moon is crossing the Earth's orbital plane
(ecliptic).
– Lunar eclipses are possible only at Full Moon phase, when
the Moon is crossing the ecliptic.
Solar and Lunar Eclipses
• Solar Eclipses
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–
–
–
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Earth moves into the Moon's shadow.
Occur only the the New Moon phase.
Visible only over a narrow path across the Earth.
Can be total, annular, or partial.
Total solar eclipses are possible because the angular size of
the Sun and Moon are very nearly equal.
• Lunar Eclipses
–
–
–
–
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Moon moves into Earth's shadow.
Occur only at the Full Moon phase.
Are visible over the entire night side of the Earth.
Can be total, partial, or penumbral.
A total lunar eclipse does not get completely black, because
some light from the Sun is bent around the Earth by the
Earth's atmosphere.
• Planetary Motions and Configurations
–all planets orbit EASTWARD around the Sun
–the further from Sun, the slower the angular speed of
the planet in orbit
–describe cause of retrograde motion, observed
planetary phases
–define configurations
• inferior planets
– conjunction
»inferior
»superior
– maximum elongation
• superior planets
– opposition,
– conjunction,
– quadrature
•Planetary Motion and Models of the Solar System
–retrograde motion
–models
•geocentric
– epicycles and deferents
•heliocentric
–historical contributions to understanding of universe
•Aristotle
•Aristarchus
•Hipparchus
•Ptolemy
•Copernicus
•Galileo
•Brahe
•Kepler
•Newton
•Kepler’s 3 Laws of Planetary Motion
– 1st Law: law of ellipses
– 2nd Law: law of equal areas
– 3rd Law: “harmonic” law (P2 a3)
– Ellipses and orbits
•eccentricity, semi-major axis, aphelion, perihelion
•Newton’s Laws of Motion and the Law of Gravity
– 1st Law: law of inertia
– 2nd Law: force law (F=ma)
– 3rd Law: action-reaction law
– Law of Gravity: gravitational force between two objects is proportional to the
product of the mass of each object divided by the distance
between their centers squared.
– Concepts:
•Acceleration due to gravity same on objects of different mass,
but force of gravity on each object is different.
•Force exerted on pebble by Earth is the same size, but opposite direction as
force exerted on Earth by pebble.
•Why does the Moon orbit the Earth when the Earth’s gravity is pulling the
Moon down toward Earth?
• Forces and Motion
– Definitions and Examples
•
•
•
•
•
•
•
•
mass,
inertia
speed
velocity
acceleration
force
gravity
weight
•Waves and Wave Motion
–definitions
•wavelength: distance between crests of a wave
•amplitude: intensity or height of a wave
•frequency: number of waves per second
•period: time between successive wave crests
(1/frequency)
•wave speed: frequency x wavelength
–transverse and longitudinal waves
–properties of waves
•reflection
•refraction
•dispersion
•diffraction
•interference: constructive, destructive
•superposition
–Doppler effect
• Electromagnetic Spectrum
– electromagnetic waves
•
•
•
•
•
created by acceleration of charged particles
transverse wave
transmit energy through space
need NO medium to propagate
all wavelengths travel at same speed in a vacuum, c = 3x105 km/s
– components in order of increasing wavelength
• gamma rays, X-rays, ultraviolet light, visible light, infrared light, radio waves
– relationship between energy, frequency, and wavelength of light
• E  f or E  1/
• high energy radiation: high frequency, small wavelengths, “blue” color
• low energy radiation: low frequency, large wavelengths, “red” color
• Kirchoff’s Laws
– relate patterns within an observed spectrum to the object producing the spectrum
– understand how features are produced
• continuous spectrum
• emission spectrum
• absorption spectrum
•Atomic Structure
–protons, electrons, neutrons
–Bohr model of atom
•“solar system” model with quantized electron energy levels
– ground state, excited states, ionization
– transitions between states
»electron “excited” by absorbing photon with right energy
»electron “de-excited” by emitting a photon
–relationship between electron energy levels and atomic spectra
•each element has unique emission/absorption spectrum
–properties of objects determined by studying spectra
they produce
•temperature, motions, composition, etc.
–sources of spectral line broadening
Example Questions
1 According to Newton, if the mass of the Earth tripled, your weight would _________.
A.
remain the same
B.
be one half of its current value
C.
be one third of its current value
D.
Three times its current value
E.
quadruple its current value
The distance between successive wave crests is defined as the _________ of that wave.
A.
frequency
B.
amplitude
C.
period
D.
wavelength
E.
wave speed
1. A comet orbiting the Sun has an aphelion distance of 90 AU and a perihelion distance of 70 AU. The semi-major axis of the asteroid's
orbit is ________.
A.
10 AU
B.
20 AU
C.
80 AU
D.
160 AU
E.
714 AU
Example Questions
If the same net force is applied to two objects, one with a mass of 10-kg and the other with a mass of 5-kg, which of the following
statements is TRUE?
A. A. The 10-kg mass will have twice the acceleration of the 5-kg mass.
B.
B. The 5-kg mass will have twice the acceleration of the 10-kg mass.
C. C. Both objects will have the same acceleration, since the force determines the acceleration.
What is emitted from an atom when one of its electrons makes a transition from a higher energy state to a lower energy state?
A.
A photon.
B.
A neutron.
C.
An electron.
D.
A proton.
E.
Nothing, the atom becomes smaller.