Electromagnetic Waves, Visible Light, Lenses and Mirrors

Chapters 12-13-14Page 354-

Wave Review

Waves

Compressional Transverse

ElectromagneticSound

Radio-Infrared-Visible-Ultraviolet-X-rays-gamma rays

• Light, radio waves, and X rays are examples of electromagnetic waves.

Electromagnetic Waves

• Electromagnetic waves are transverse waves.

• They contain electric and magnetic parts that vibrate up and down perpendicular to the direction the wave travels.

• Electromagnetic waves can travel through space or through matter.

Producing EM Waves (cont)

• Electromagnetic waves are produced when an electric charge is vibrating.– Vibrating electric charges are surrounded by

vibrating electric and magnetic fields.– Vibrating electric and magnetic fields travel

outward from the moving charge.

Properties of Light Waves• An electromagnetic wave contains an

electric part and a magnetic part.• Both parts are called fields and

vibrate at right angles to the wave motion.

EM waves are transverse waves

• EM waves carry radiant energy• EM waves are characterized by frequency,

wavelength and velocity.• V= λ f • Speed of light is a constant in any medium• As frequency increases, wavelength decreases

– Frequency is the number of vibrations per second– Wavelength is the distance between crests

The Speed of Light• In empty space (vacuum), light travels at a

speed of about 300,000 km/s. • Light travels so fast that light emitted from

the Sun travels 150 million km to Earth in only about eight and a half minutes.

• When light travels in matter, it interacts with the atoms and molecules in the material and slows down.

• As a result, light travels fastest in empty space, and travels slowest in solids.

The Electromagnetic Spectrum• At one end of the spectrum the waves have low

frequency, long wavelength, and low energy. At the other end the waves have high frequency, high energy and short wavelengths.

Long Wavelength Short Wavelength

Low FrequencyLow Energy

High FrequencyHigh Energy

Radio Waves and Microwaves• The wavelengths of radio waves are greater

than about 0.3 meters.

• Some are even thousands of meters long.

• The shortest radio waves are called microwaves.

• These waves have a wavelength between about 0.3 meters and 0.001 meters.

Infrared WavesInfrared waves have wavelengths between

0.001 meters and 700 billionths of a meter. • All warm bodies emit infrared waves. • Law enforcement officials and military

personnel sometimes use special night goggles that are sensitive to infrared waves. These goggles can be used to help locate people in the dark.

Visible Light and Color• The range of electromagnetic waves between

700 and 400 billionths of a meter is the range of wavelengths people can see.

Ultraviolet Waves

• Electromagnetic waves with wavelengths between about 400 billionths and 10 billionths of a meter are ultraviolet waves.

• Ultraviolet waves carry more energy than visible light waves.

• Sunlight that reaches Earth’s surface contains a small fraction of ultraviolet waves.

X Rays and Gamma Rays• The electromagnetic

waves with the highest energy, highest frequency, and shortest wavelengths are X rays and gamma rays.

• X rays pass through soft tissues, but are blocked by denser body parts, such as bones.

X Rays and Gamma Rays

• Gamma rays are even more energetic than X rays.

• One use of gamma rays is in the food industry to kill bacteria that might increase the rate of spoilage of food.

• Gamma rays are dangerous because they can break down molecules and cells.

Chapter 12 Assignments

• Notetaking Worksheet• Chapter Review

– Page 378-379, 8-16, 26,28

Seeing is ReflectingPage 384

• To see an object:– It must produce light– Or Reflect light

• All objects– Reflect light– Absorb light

• Some Transmit light (refract)

Matter and Light

• Absorb, Reflect, Refract (transmit)• Materials that absorb and reflect light are called

opaque.• Materials that refract and absorb light

irregularly are called translucent. Translucent materials allow some light to pass through.

• Materials that refract (transmit) most of the light are called transparent.

Opaque

Translucent

Transparent

Reflected LightPage 385

• Reflection- a light wave strikes an object and bounces off.

• Angle of reflection = angle of incidence• Regular Reflection – mirrors – reflect light in

single direction and form sharp images.• Diffuse Reflection- irregular surfaces like brick

walls reflect light in many different directions and do not form an image.

• We see objects because they reflect light.

The Law of Reflection• According to law of reflection, the angle that the

incoming wave (incident) makes with the normal equals the angle that the outgoing (reflection) wave makes with the normal.

θrθi

θi= θr

Incident angle= Reflection angle

Regular Reflection

Irregular Reflection

Refracted LightPage 386-387

• Refraction- change in speed of a light wave when it passes from one material into another.

• Light rays are bent as they pass from one material into another.

• Index of Refraction- indicates how much a material reduces the speed of light;

• The more light is slowed, the higher the index of refraction.

Refraction of Light

Refraction by a Prism

Color (Page 389)

• When white light (mix of all colors) falls on an object, some colors are absorbed, some are reflected.

• We see objects in the color that is reflected by the object.

• The other colors are absorbed.• The colors that are absorbed or reflected

depend on the material.

Mixing Color

Light Pigments

Wave/ParticlePage 359

• Different experiments show light to have different natures.

• Young’s Interference Experiment show light to behave as a wave.

• Photoelectric effect experiments show light to behave as a particle

• Photon- a packet (particle) of wave energy

Light Schedule

• Monday 3/11 Chapter 14 Mirrors/Lenses• Tuesday 3/12 Chapter 13 NTWS, Review• Wednesday 3/13 Mirror Lab• Thursday 3/14 Lens Lab• Friday 3/15 Chapter 14 NTWS, Review• Monday 3/18 Light Review• Tuesday 3/19 Light Test (Chapter 12-14)

Chapter 13 Assignments

• Notetaking Worksheet- Light• Chapter Review page 410-411: 6-13

• Due Tuesday 3/12

Chapter 14 P416-437• Section 1 Mirrors P416

– Flat– Concave- Converging– Convex- Diverging

• Section 2 Lenses P424– Convex Lens- Converging– Concave Lens- Diverging

• Assignments– NTWS/Practice Sheet– Review Page 442-443: 6-9,15,16– Lab

Image Formed by a Flat Mirror

Images

• Real – light rays actually pass through the point where the image is formed.

• Virtual – light rays appear to pass through the point where the image is formed but actually do not.

• Upright – Inverted• Reversed• Enlarged-Reduced

Mirrors

Flat or Plain

Concave

Convex

Curved Mirrors• Focal point – the point where parallel incident

rays converge when they are reflected.– For a concave mirror, the focal point is on the

same side as the source of light rays.– For a convex mirror the focal point is behind the

mirror from the source of the light rays.• Center of curvature- the center of the circle

from which the mirror is made.• Focal length is ½ the radius of curvature.

– Focal point is ½ way between center of curvature and the mirror.

3 Rays (any 2)

• A ray passing through the focal point will be reflected parallel to the axis of the mirror.

• A ray parallel to the axis will be reflected through the focal point.

• A ray passing through the center of curvature of a mirror will be reflected back on itself.

Concave Mirror Image

Convex Mirror Image

Lenses

Concave-Concave Convex-Convex

Lens Ray Diagrams

• A light ray passing through the focal point of a lens is refracted out of the lens parallel to the axis.

• A light ray parallel to the axis of the lens is refracted out of the lens through the focal point.

• A light ray passing through the center of a lens goes straight through the lens.

Outside center of Curvature

At or inside Center of Curvature

Inside the Focal Length

Converging Lens

Diverging Lens