WELCOME TO PERIOD 20: RADIANT ENERGY FROM THE SUN

Transcription

1 WELCOME TO PERIOD 20: RADIANT ENERGY FROM THE SUN Homework #19 is due today. Midterm 2: Weds, Mar 27, 7:45 8:55 pm (Same room as your midterm 1 exam.) Covers periods and videos 3 & 4 Review: Tues, 3/26, 7:00 8:00 pm 2005 SM Drop in: Weds, 3/27, 5:30 7:15 pm 2005 SM Be sure to bring a calculator to the exam!

2 PHYSICS 1104 PERIOD 20 How is radiant energy produced in the Sun? How does this energy reach the Earth? What properties of waves made energy transfer possible?

3 Kinetic Thermal Sound Electrical Magnetic Radiant Gravitational Strain Chemical Electrical Nuclear Summary of the forms of energy The energy exhibited by objects in motion. The unorganized energy of motion of vibrating atoms and molecules. The organized energy of motion of vibrating atoms and molecules. The energy resulting from forces between charged particles. The energy resulting from the forces between magnets. The energy resulting from vibrations of electric charge, such as radio waves, microwaves, or visible light. The energy stored in raised objects that could fall. The energy stored in a stretched or compressed spring. The energy available in the chemical bonds binding atoms together. The energy stored by static electric charges. Energy available in the nuclei of radioactive atoms.

4 Energy from electric charge Stationary electric charge produces an electric force and has electric potential energy. Moving electric charge produces an electric current. Vibrating electric charge produces radiant energy. (Radiant energy is also called electromagnetic radiation.)

5 Radiant energy (electromagnetic radiation) Radiant energy results from vibrations of charges. As the charges vibrate, they produce waves of energy. Waves of electromagnetic radiation travel at a speed of 3 x 10 8 (300,000,000) meters/second in a vacuum.

6 The type of radiant energy depends on the wavelength. Shorter wavelengths transmit more energy than longer wavelengths.

7 Types of electromagnetic radiation The electromagnetic spectrum can be divided into types of radiant energy based on the wavelength and frequency. The spectrum from the longest wavelength to the shortest: 1) Radio waves used for radio and TV transmission. 2) Microwaves used for communication and in microwave ovens. 3) Infrared radiation, which we experience as thermal energy. 4) Visible light waves are a small portion of the spectrum 5) Ultraviolet light that causes skin tanning 6) X rays used in medical applications 7) Gamma rays produced in some nuclear reactions.

8 Visible light spectrum Source:

9 Some insects can see ultraviolet light Humans see yellow flowers in visible light. On the same flowers, bees can see patterns in ultraviolet light. Source: ciencetech/article /abees-eye-view-how-insectsflowers-differently-us.html

10 Nucleons = quark trios Quarks are fundamental particles. up quark = + 2/3 charge; down quark = - 1/3 Proton consists of 2 up quarks and 1 down quark. Neutron consists of 1 up quark and 2 down quarks. For two quarks of the same type (2 up quarks or 2 down quarks), their spins must point in opposite directions. The gluon is the gauge boson responsible for the strong nuclear force that holds three quarks together to form a neutron or a proton.

11 Beta decay involves a change in quarks b+ decay: A proton changes into a neutron. b- decay: A neutron changes into a proton. energy e n p 0 o energy e p n

12 Fusion Combining of nucleons or small nuclei Exothermic Fission Breaking apart of large nuclei Exothermic Total number of nucleons

13 Fusion in stars: the proton-proton chain Stars smaller than 1.2 times the mass of the Sun use a hydrogen-burning proton-proton chain as their primary fusion process. 1) two hydrogen nuclei (protons) fuse to form a nucleus of deuterium. 1 H + 1 H 2 H + e + + e (+1.44 MeV) 2) Deuterium fuses with another hydrogen to form an isotope of helium called tritium. 2 H + 1 H 3 He + ( MeV) 3) Two tritium fuse to form a stable helium nucleus plus two hydrogen nuclei. 3 He + 3 He 4 He + 1 H + 1 H ( MeV)

14 Energy release in a star Convective zone: hotter gases rise toward to the surface. Cooler gases drop inward. Nuclear burning region: fusion in the core of a star releases energy. Radiative zone: energy transfer by radiation occurs when photons randomly scatter.

15 Shape of stars The gravitational force exerts an inward pressure on the core of a star. Thermal energy from the core transferred to the star surface produces outward radiation pressure. In a stable star, the outward radiation pressure of the hot gas is balanced by the inward force of gravity. Inward force of gravity Outward force of radiation pressure

16 Wave properties Wavelength and amplitude of a sine wave. Wave Length Wave height (amplitude) Distance Wave Length

17 Wavelength, period, and frequency The wave s period is the time it takes to complete one cycle. The wave s frequency is how often it completes a cycle. Wave Length Wave Length Distance Wave Period Wave Period Time Lower frequency Higher frequency

18 Wave frequency The period of a wave is the time it takes the wave to complete one cycle. The frequency of a wave is the inverse of its period. frequency = 1/period Frequency is measured in Hertz (Hz) 1 Hz = 1 cycle/second

19 Wave speed The relationship between wavelength and frequency gives the speed of a wave: s = f L s = speed at which radiant energy travels (meters/sec or mi/sec) f = frequency (cycles/sec, or Hertz) L = wavelength (in meters, miles, or feet)

20 Electromagnetic waves and sound waves Which type of waves can travel through air? Which type of waves can travel through a vacuum? How do the speeds of sound waves and electromagnetic waves compare?

21 BEFORE THE NEXT CLASS Read textbook chapter 21. Complete Homework Exercise 20. Print out Activity Sheet 21. Midterm 2: Weds, Mar 27, 7:45 8:55 pm (Same room as your midterm 1 exam.) Covers periods and videos 3 & 4 Review: Tues, 3/26, 7:00 8:00 pm 2005 SM Drop in: Weds, 3/27, 5:30 7:15 pm 2005 SM Be sure to bring a calculator to the exam!