Nuclear Atom and Unanswered Questions

• Rutherford– Positive charge in the middle surrounded by

fast moving electrons– How come the electrons don’t get pulled into

the middle?– Why do different elements behave differently?

Early 1900’s

• Scientists made some observations– Certain elements emitted visible light when

heated in a flame– Elements chemical behavior is related to the

arrangement of electron in its atoms– Relationship between atoms and light

Light

• Electromagnetic radiation– Form of energy that exhibits wavelike

behavior as it travels through space• Ex) Visible light, microwaves, X-rays, radio

waves…

Waves

• What is a wave?– A traveling rhythmic disturbance– Carries energy from place to place without

requiring matter to travel across the in-between distance

• Matter does not move from one place to another, the disturbance (wave) does.

• Sound and light travel in waves

Wave Basics

• Crest – the highest point above the rest position.

• Trough – the lowest point below the rest position.

Speed of a Wave• Wavelength (λ) – the distance between a

point on one wave and the same point on the next wave cycle.

• Speed = Wavelength x Frequency (s=λf)– Unit = m/s (meters per second)

Parts of a wave

• Amplitude – (A) wave height – relates to the intensity of the light

• Wavelength (λ) – distance between two adjacent peaks

• Frequency ( ν) – the number of wavelengths (or wave cycles) that pass a given point in one second– Hertz (Hz) – unit for frequency; a wave that sends1

crest (or 1 wave cycle) by a point every second would be ν = 1Hz or “1/ s”

• Velocity – speed of light = c = 3.00x108m/s

Amplitude Example

• The more energy a wave has, the greater is its amplitude.

The Waves of the Spectrum

• The full range of frequencies of electromagnetic radiation is called the Electromagnetic Spectrum.

Visible Light

• Visible light is light is the part of the EM spectrum the human eye can see.

• Each color corresponds to a specific frequency and wavelength.

Complete the worksheet while watching the movie.

Homework Book Questions

• Read, notes, and vocabulary for 6.2

• 6.9, 6.13, 6.15, 6.17, 6.18

• Due Monday

Visible Light

• Small part of the electromagnetic spectrum

• Short wavelengths bend more than long wavelengths as they pass through the prism

• Results in the rainbow we see (ROY G BIV)

• Energy increases with increasing frequency

PracticeWhich of the below waves has …

– the higher frequency?– the longer wavelength?– If one wave represented red light and one

represented blue light which would be which?– Which one would have more energy???

EM Spectrum

• Bigger slower to shorter faster (more harmful)

Wave speed

• Speed, frequency and wavelength are related and give us an understanding of the energy of the wave!!!

speed of light = frequency x wavelength

c (in meter/second) = ν (in hertz) x λ (in meters)

c = v x λ

Practices problems

• Red light has a wavelength of 722nm, what is the frequency of the light?

• Don’t forget to convert nm to m.

• An electromagnetic wave is measured to have a frequency of 4.7x1013Hz. Calculate its wavelength and identify the type of wave.

Things wave model of light cannot explain

1) Black-Body radiation- Emission of light from hot objects

2) Photoelectric effect- Emission of electrons from metal surfaces on which

light shines

3) Emission line spectra- Emission of light from electronically excited gases

i.e. tungsten metal emits bright white light when heated

i.e. red glow of electric stove burner

Quantum Concept

• Max Planck said energy can be either released or absorbed by atoms ONLY in discrete “chunks” of some minimum energy

• Quantum meaning “fixed amount” is the smallest quantity of energy that can be emitted or absorbed as electromagnetic radiation

Quantum ConceptThe ball can only have

certain amounts of potential energy when at rest.

The potential energy of the ball at rest is quantized.

The ramp is an example of a continuous situation in which any energy state is possible up the ramp

Like a set of stairs, the energy states of an electron is quantized – i.e. electrons are only found on a specific step

Einstein used quantum theory to explain photoelectric effect.

When photons of significant high energy strike a metal surface – electrons are emitted from the metal

Photocell - emitted electrons are drawn toward positive terminal creating an electrical circuit

Quantum Concept

• Planck proposed that the energy (E) of a single quantum is equal to a constant (Planck’s constant (h)) times the frequency of the radiation.

• Planck’s constant = h = 6.626x10-34 Joule-second (Js)

Energy of quantum = Planck’s constant x frequency

E = h v

Practice Exercises

• A laser emits light with a frequency of 4.69x1014 s-1. How much energy is emitted from one quantum of the radiation from this laser?

• Calculate the energy of one photon (quantum) of yellow light whose wavelength is 589nm.

• Matter can only gain or lose energy in small specific amounts.

• Quantum – Minimum amount of energy that can be

gained or lost by an atom.

Homework Book Questions

• Read, notes, and vocabulary for 6.2

• 6.9, 6.13, 6.15, 6.17, 6.18

Quantum Concept

• Glowing light emitted by hot objects

• As the object is heated it gains energy…

• As the object gains it changes colors (emits different colors)

EM Spectrum Drawing

• Where is red in the rainbow? Why?• Where is violet in rainbow? Why?• Pick something to draw.

– You are given the wavelengths of each color (on sheet)

– Determine a scale that you are going to use to draw• Convert nm to mm

– Convert wavelengths of each color to frequency– Convert frequency to energy (think Planck)– All work must be shown on back to receive credit

Planck

• Proposed that emitted light was quantized

• Energy of a quantum is related to the frequency of the emitted radiation

E (quantum) = h v

E=energy

H= planck’s constant

V= frequency

Wave or Particle?• Electromagnetic radiation

behaves sometimes like a wave and sometimes like a stream of particles.

Photoelectric Effect

• Beam of light has many wave like characteristics…

• It can also be thought of as stream of tiny particles or bundles of energy

• Photons– Particle of electromagnetic radiation with no

mass that carries a quantum of enrgy– E (photon) = h v

Atomic Emission Spectrum

• Set of frequencies of the electromagnetic waves emitted by the atoms of the element

• Each element’s atomic emission spectrum is unique– Used to determine unknowns (forensics)

5.1 Worksheet

• Complete 5.1 worksheet using only your notes.

Interactions of Light

• When light strikes a new medium, the light can be reflected, absorbed, or transmitted.

• When light is transmitted, it can be refracted, polarized, or scattered.