ThursdaySeptember 22,

2011(The Dual Nature of

Electromagnetic Radiation; Plank’s

Constant)

Bell RingerThursday, 9-22-11

What is electromagnetic

radiation?

The entire range of radiation including, in order of decreasing frequency, gamma rays, x-rays, ultraviolet radiation, visible light, infrared radiation, microwaves,

and radio waves.

Explain why passing electricity though a tube filled with gas causes the

gas to glow.

Introduction of electrical energy causes the electrons in the gas atoms

to jump up to higher energy levels. When these “excited” electrons fall back down to their original “ground state” energy levels, they emit the

extra energy in the form of photons of light at a certain frequency and color,

causing the glow.

Assignment Currently OpenNotebook

Page

Date of Notes on Website

Date Issued

Date Due

Late Date to

Remediate

Lab – Properties of Matter: Density of Metals TBD 9/7 9/7 9/9

Lab – Identifying Substances and Mixtures TBD 9/9 9/9 9/13

Lab – Physical Properties of Matter TBD 9/12 9/12 9/14

Lab – Chemical Properties of Matter TBD 9/14 9/14 9/16

WS – Categories, Properties, and Phases of Matter TBD 9/15 9/15 9/20

Test 1 TBD 9/16 9/16 9/16 9/30

WS – What’s in the Atom TBD 9/19 9/19 9/20

Project – Atomic Structure N/A 9/20 9/20 9/26 N/A

Do you need to remediate Test 1?

Are you working on your Atomic Structure

project?

Announcements

A German physicist named Max Planck was studying the emission

of light by hot objects.

He proposed that a hot object does not emit electromagnetic energy

continuously, as would be expected if the energy emitted

were in the form of waves.

Instead, Planck suggested that the object emits energy in small,

specific amounts called “quanta.”

A quantum is the minimum quantity of energy that can be lost or gained

by an atom.

The Particle Description of Light

Planck proposed the following relationship between a

quantum of energy and the frequency of radiation.

E = hνIn the equation, E is the

energy, in joules, of a quantum of radiation, v is the frequency of the radiation emitted, and h

is a fundamental physical constant now known as

Planck’s constant

h = 6.626 × 10−34 J¢s.

The Particle Description of Light

In 1905, Albert Einstein expanded on Planck’s theory by introducing the radical idea that electromagnetic radiation

has a dual wave-particle nature.

While light exhibits many wavelike properties, it can also

be thought of as a stream of particles. Each particle of light carries a quantum of energy.

Einstein called these particles “photons.”

The Particle Description of Light

A photon is a particle of electromagnetic radiation

having zero mass and carrying a quantum of energy.

The energy of a particular photon depends on the

frequency of the radiation.

Ephoton = hvEinstein explained the photoelectric effect by

proposing that electromagnetic radiation is absorbed by matter

only in whole numbers of photons.

The Particle Description of Light

In order for an electron to be ejected from a metal surface, the electron must be struck by a single photon possessing at least the minimum

energy required to knock the electron loose.

According to the equation Ephoton = hv, this minimum energy corresponds to a

minimum frequency. If a photon’s frequency is below the minimum, then

the electron remains bound to the metal surface.

Electrons in different metals are bound more or less tightly, so different metals require different minimum frequencies

to exhibit the photoelectric effect.

The Particle Description of Light

The Least You Need to Know

Light (all EM radiation) has a dual nature. Light can travel as a wave or a particle. The wave and particle natures

are related by Plank’s formula, E = hv.

Homework

… continue working on your Atomic Structure project with

your partner.