Physics

Unit 11

Electromagnetic Waves (What are they?)

Transverse waves created by oscillating electrical and magnetic fields

Electromagnetic Waves (transmitting/transferring energy)

Energy is transferred by photos and does not require a medium to transmit

Higher frequency = ??? energy

more energy transferred

Electromagnetic spectrum (categorization)

Categorized by wavelength and frequency, longest wavelength to shortest

Electromagnetic Spectrum (Order)

Radio Waves → Infrared →Visible Light →Ultraviolet → X-rays → Gamma Rays

Radio Waves (Properties)

Longest wavelengths, lowest frequency and energy

TV

Radio Waves

Radio Signal Transmission

Radio Waves

Satellite Communications

Radio Waves

Radio telescopes to study celestial objects

Radio Waves

Microwaves (characteristics)

High-frequency radio waves with unique properties

Used in microwave ovens to heat food

Microwaves (screen door prevents waves from escaping)

Causes water molecules to spin, increasing energy

Microwaves ( Microwave-safe cookware does not contain water, so it does not heat )

Infrared Waves (Properties)

Higher frequency and energy than radio waves, detected as heat

Infrared heaters

Infrared Waves

Remote controls

Infrared Waves

Thermal imaging cameras

Infrared Waves

Night-vision goggles

Infrared Waves

Can causes skin damage and skin cancer

Ultraviolet Rays (Properties)

Ozone layer blocks most harmful UV waves

Ultraviolet Rays (Properties)

Sterilization devices (kills microorganisms)

Ultraviolet Rays

Hospital Sanitization

Ultraviolet Rays

Water and surface sanitizing

Ultraviolet Rays

Tanning beds

Ultraviolet Rays

X-Rays (Properties)

High energy, can penetrate soft tissue but not dense materials

Medical imaging

X-Rays

Airport luggage scanning

X-Rays

Detecting cracks in building structures

X-Rays

Gamma Rays (Properties)

Most energetic and most harmful waves on the spectrum

High-level sterilization procedures

Gamma Rays

Radiation therapy for cancer treatment

Gamma Rays

Emitted from nuclear explosions

Gamma Rays

As frequency increases.. (wavelength, energy, potential harm)

Wavelength decreases

Energy increases

Potential harm increases

Electromagnetic Radiation (What are they?)

waves caused by alternating electric and magnetic fields

Electromagnetic Radiation (Categorized by..)

Frequency and wavelength

Photoelectric Effect (What is it and what happens?)

Wave of a certain frequency interacts with metal surface

An electron is ejected from the metal, ejected electron is called a photoelectron

Photoelectric Effect (Discovery)

As UV light struck metal, light intensity did not affect emission

Only frequency mattered for electron ejection

How did Einstein propose light’s behavior as both wave and particle?

Light has set amount of energy

Particle: carries energy proportional to frequency

Wave: has frequency determined by particle’s enery

Photon Energy Equation

E = hf

E: energy of a photon

h: Planck’s constant ( 6.6 × 10^-34 )

f: frequency of light

Threshold Frequency

Minimum frequency needed to eject an electron

Higher frequency waves have more energy

Not all light frequencies cause electronic emission, different metals have different threshold frequencies

Work Function (Φ)

The minimum energy required to extract one electron from a metal

Photoelectron Kinetic Energy Equation

KE = hf - Φ

h: Planck’s constant

f: frequency of incoming light

Φ: work Function of metal

Predicting Electron Emission (how)

Calculate photon energy using E = hf

Compare to work Function of metal

If E > Φ, photoelectron can be emitted
If E < Φ, no electron emission occurs

Emission Spectra (energy levels)

Electrons exist at specific energy levels and move to higher levels when energy is absorbed

Electrons return to ground state and emit photons

Atomic Emission Spectra

Specific wavelengths emitted by each element with unique emission spectrum

Acts as a “fingerprint” to identify elements

Light as a Wave

Light is an electromagnetic wave

Exhibits wave properties and behaviors

Light as a Wave (behaviors)

Reflection, Refraction, Diffraction

Reflection of Light

Occurs when light rays bounce off a surface

Specular Reflection

Smooth surfaces (mirrors)

Diffuse Reflection

Rough surfaces (paper, walls)
Allows us to see objects around us

The Law of Reflection

Angle of incidence = Angle of reflection

Both angles measured from normal line (perpendicular 90 degree surface)

θ = θ

θ: Angle of incidence

θ: Angle of reflection

Both measured from normal line

Refraction of Light (what is it? Occurs when and how?)

Bending of light as it passes between media

Occurs when light speed changes in different materials

Light bends towards normal in denser medium

Light bends away from normal in less dense medium

Index of Refraction + equation

measures how much light slows down in a material

n = c / v (speed of light in vacuum / speed in medium)

Higher n = light travels slower = denser medium

Snell’s Law

nsin(θ) = nsin(θ)

n, n: indices of refraction

θ: Angle of incidence

θ: Angle of refraction

Total Internal Reflection (occurs)

Occurs when light travels from high to low index medium

Total Internal Reflection (critical angle)

At critical angle, reflected ray travels along boundary

Beyond critical angle, all light reflects internally

Total Internal Reflection (applications)

fiber optic cables

Diffraction of Light

The spreading of light waves around obstacles and through openings

Single Slit DIffraction

Light passes through narrow slit, creates diffraction pattern on distant screen

Huygens’ Principle

Each part of slit in single slit diffraction acts as wave emitter

Interference Patterns (constructive & destructive)

Constructive interference: crest meets crest (bright)

Destructive interference: crest meets trough (dark)

Young’s Double Slit Experiment

Light passes through 2 narrow slits and waves from each slit diffract and overlap

Which 2 describe ways electromagnetic waves interact with matter?

Gravitation Absorption Photosynthesis Refraction

Absorption & Refraction

What part of the EM spectrum is a thermal camera detecting radiation emitted by warm objects?

Infrared

If a low-frequency light is shone on a metal surface and no electrons are emitted, how 2 emmit electrons?

Increase the frequency of the light

Polarized light

light that vibrates primarily in a single plane

Which 2 of these produce polarized light?

Light reflecting off a nonmetallic surface (like water)

Sound waves passing through air

A magnet near a flashlight changing the color

Light passing through a polarizing filter

Light reflecting off a nonmetallic surface (like water)

and

Light passing through a polarizing filter

Electromagnetic waves in a vacuum

All electromagnetic waves travel at da same speed

Which electromagnetic wave has the greatest photon energy?

Gamma Rays

When an electron in an atom drops from a higher energy level to a lower energy level, the atom releases energy as

A photon of light

Remote control

Infrared

Why do different elements produce different line patterns in emission spectra?

Each element has unique allowed electron energy levels

In da photoelectric effect, increasing light intensity while keeping frequency above threshold increases da

number of emitted electrons

Which 2 factors affect the pattern (positions) of bright lines in an atomic emission spectrum?

Whether the room lights are on

How many atoms are in the sample (only)

The set of possible energy-level transitions

Which element is present

The set of possible energy-level transitions

and

Which element is present

In da photoelectric effect, maximum kinetic energy of emitted electrons depends on da light’s…

frequency