1.1.3 Explain how the sun produces energy which is transferred to the Earth by radiation. Sun’s Energy

Combustion and Nuclear Reactions 1.1.3a Compare combustion and nuclear reactions (fusion and fission) on a conceptual level. Identify fusion as the process that produces radiant energy of stars. Combustion and Nuclear Reactions

Table: Fission Fusion Definition

Definition Fission is the splitting of a large atom into two or more smaller ones. Fusion is the fusing of two or more lighter atoms into a larger one. Fusion demo

Natural Processes Fission reaction does not normally occur in nature. Fusion occurs in stars, such as the sun.

Byproducts of the reaction Fission produces many highly radioactive particles. Few radioactive particles are produced by fusion reaction, but if a fission "trigger" is used, radioactive particles will result from that.

Conditions Critical mass of the substance and high-speed neutrons are required for fission. (Think “enriched” uranium) High density, high temperature environment is required for fussion.

Energy Requirements Takes little energy to split two atoms in a fission reaction. Extremely high energy is required to bring two or more protons close enough that nuclear forces overcome their electrostatic repulsion.

Energy Released The energy released by fission is a million times greater than that released in chemical reactions; but lower than the energy released by nuclear fusion. The energy released by fusion is three to four times greater than the energy released by fission.

Nuclear Weapons One class of nuclear weapon is a fission bomb, also known as an atomic bomb or atom bomb. One class of nuclear weapon is the hydrogen bomb, which uses a fission reaction to "trigger" a fusion reaction.

Warmup What is the difference between fusion and fission? Which one occurs on the sun?

Warmup How many high tides do we have each day (24hrs)? Why? What is the difference between fusion and fission? Which one occurs on the sun?

Energy Produced by the Sun 1.1.3b Identify the forms of energy (electromagnetic waves) produced by the sun and how some are filtered by the atmosphere (X-rays, cosmic rays, etc.). Energy Produced by the Sun

What is an Electromagnetic Wave? Electromagnetic waves can transfer energy without a medium An electromagnetic wave consists of vibrating electric and magnetic fields that move through space at the speed of light

Producing Electromagnetic Waves Electromagnetic waves are produced by charged particles Every charged particle has an electric field surrounding it The electric field produces electric forces that can push or pull on other particles

Producing Electromagnetic Waves When a charged particle moves it produces a Magnetic field A magnetic field can exert magnetic forces that can act on certain materials Example: If you place a paper clip near a magnet, the paper clip will move toward the magnet because of the magnetic field surrounding the magnet.

Producing Electromagnetic Waves When a charged particle changes its motion, its magnetic field changes The changing magnetic field causes the electric field to change When one field vibrates, so does the other **The two fields constantly causes each other to change and this produces an Electromagnetic wave**

Energy Electromagnetic Radiation is the energy that is transferred through space by electromagnetic waves Electromagnetic waves transfer energy through a vacuum, or empty space Example: You can see the stars and sun because their light reaches the Earth through the vacuum of space

Tools of Astronomy Radiation It includes visible light, infrared and ultraviolet radiation, radio waves, microwaves, X rays, and gamma rays.

Speed All electromagnetic waves travel at the same speed in a vacuum = 300,000 km/s This speed is called the speed of light At this speed, light from the sun takes about 8 minutes to travel to the Earth (150 km) Light waves travel more slowly in air

Models of Electromagnetic Waves Many properties of electromagnetic waves can be explained by a wave model Some properties are best explained by a particle model Both a wave model and a particle model are needed to explain all of the properties light

Wave Model of Light Light acts as a wave when it passes through a polarizing filter Ordinary light has waves that vibrate in all directions-up and down, left and right, and at all other angles A polarizing filter acts as though it has tiny slits that are aligned in one direction

Wave Model of Light Only some light waves pass through a polarizing filter. Light that passes through and vibrates in only one direction is called polarized light No light passes through two polarizing filters that are placed at right angles to each other

Wave Model of Light To better understand the wave model of light… Think of waves of light as being transverse waves on a rope If you shake a rope through a fence with vertical slats, only waves that vibrate up and down will pass through If you shake the rope side to side, the waves will be blocked A polarizing light filter acts like the slats in a fence. It only allows waves that vibrate in one direction to pass through

Particle Model of Light Sometimes light behaves like a stream of particles When a beam of light shines on some substances it causes tiny particles called electrons to move The movement of electrons causes an electric current to flow

Particle Model of Light Sometimes light can even cause an electron to move so much that it is knocked out of the substance This process is called the photoelectric effect

Particle Model of Light The photoelectric effect can be explained only by thinking of light as a stream of tiny packets, or particles of energy Each packet of light energy is called a photon Albert Einstein first explained the science behind the photoelectric effect in 1905