Intro to Physics

2nd semester topics for final exam pt. 2

Waves

Mechanical waves• Fastest through solids,

slowest through gases• Can only travel through

matter• Ex: sound, seismic waves

Non-mechanical waves• Fastest through a vacuum,

slowest through solids• Can travel through matter

or space• Ex: electromagnetic waves

ARE THERE DIFFERENT TYPES OF WAVES?

• Mechanical Waves • Non-Mechanical Waves

microwavesSound waves

Electromagnetic Wave

http://www.nrc-cnrc.gc.ca/obj/inms-ienm/images/research_images/optical_comb/COMBFIG1.gif

Waves

Transverse• Vibrations occur

perpendicular to wave travel

• Crest, trough structure

Longitudinal• Vibrations occur in same

direction as wave travel• Compression-rarefaction

structure

TRANSVERSE WAVE

crest

trough

amplitude

Onewavelength

Rest position

LONGITUDINAL WAVE

Compression (more dense)

Rarefaction (less dense)

one wavelength

Wave Characteristics

Wave Characteristics

– Frequency (f) (the number of vibrations that occur in a given time)• Hertz (Hz) (# of vibrations per second)• High frequency waves produce waves with

short periods and short wavelengths– Period (P) (the time it takes for one wave cycle to

pass)• Seconds (s)• The lower the frequency, the longer the period

Wave Characteristics– Wavelength λ (lambda) (the distance between one

point on a wave to the next identical point; crest to crest, for example)

• Meters (m) • The lower the frequency, the longer the wavelength

– Amplitude (longitudinal waves—the tightness of the compression; transverse waves—the distance from the crest to rest position or from trough to rest position)

• Meters (m)• The greater the amplitude of the wave, the more

energy the wave transfers.

Sound waves

Sound waves and the EarWhat is the audible range of frequencies for a human?

20 -20,000 Hz

What type of wave is a sound wave?

Mechanical and

Longitudinal

Relative intensity of sound wave is volume and is measured in decibels (dB)

The frequency of a sound wave is called pitch.

Like all mechanical waves, sound waves can only travel through matter

Seismic waves

Cause

• Any physical disturbance that causes the Earth to vibrate

– Earthquakes (most commonly)– Volcanoes– Landslides (terrestrial or undersea)– Extraterrestrial impacts (asteroids – and meteorites)

Earthquakes

• Earthquakes occur when built-up stress is suddenly released.

• Rupture or slippage of rock within the Earth produce seismic waves

http://quake06.stanford.edu/centennial/tour/stop11.html

• The point on Earth’s surface directly above the focus is the epicenter.

EarthquakesEarthquakes

22

• Earthquake waves travel out in all directions from a point where strain energy is released. This point is the focus.

Earthquake Waves

22

Primary waves, also called P-waves, are longitudinal waves (compressional).

• P-waves pass through solids and liquids

Body Waves—

seismic waves that pass through the Earth

• P-waves are faster than s-waves.

Secondary waves, also called S-waves are transverse waves.

• S-waves can travel through solids but not liquids

• S-waves are slower than p-waves

Fig. 9-8, p. 194

Body

Fig. 9-10, p. 196

Fig. 1-14, p. 18

Three types of plate boundaries1. Divergent plate boundary 2. Convergent Plate Boundary 3. Transform Plate

boundary

Fig. 1-12, p. 15

The Mechanism for Plate Motion is Convection in the Mantle

Heat from the interior flows outward toward the crust

Fig. 9-21, p. 210

P-waves and S-waves provide seismic evidence that the outer core is liquid and the inner core is solid

Refraction: the bending of a wave as it passes from one medium to another

Caused by changes in wave speed

Benioff Seismic Zone(associated with a subduction zone at a Convergent Plate

Boundary)

Pattern of earthquake occurrences indicates the location of the subducted limb of the lithospheric plate

Fig. 2-13, p. 37

Electromagnetic Spectrum

Increasing photon energy

WHAT CAUSES Electromagnetic waves (or LIGHT)?

• Vibrating electrically charged particles • A changing electric field sets up a

changing magnetic field, which sets up a changing electric field, and so on.

Electromagnetic wave (a combination of electric and magnetic fields

HOW DO WE MODEL LIGHT?

• TWO MODELS– Wave Model– Particle Model

• Physicists recognize the dual nature of light (light travels like a wave, but hits like a particle).

• Photon: a massless particle of light (carries energy—greater the frequency, the greater the photon energy)

INTENSITY OF LIGHT

• An increase in the number of waves or photons (or the amount of light)

• Brightness of light means intensity. • Not related to frequency or the energy

per photon!

100 Watts 40 Watts

Same frequencies of light, just different intensities!

Photoelectric Effect: the ejection of electrons from certain metals when exposed to certain frequencies of light.

Electromagnetic radiation (visible light range)

Electrons emitted

Produces electron flow (electricity)

Photovolatic cell (solar cell)

Incident rays and reflected rays make equal angles with a line perpendicular to the surface, called the normal.

• The angle between the incident ray and the normal is the angle of incidence.• The angle between the reflected ray and the normal is the angle of reflection.• Angle of incidence = Angle of reflection

29.2 The Law of Reflection

Diffuse reflection allows us to see most things around us. a. Light is diffusely reflected from paper in many directions. b. Light incident on a smooth mirror is only reflected in one direction.

29.4 Diffuse Reflection

Ordinary paper has a rough surface when viewed with a microscope.

As a light wave passes from air into water, its speed decreases.

29.8 Refraction of Light

Refraction

• The bending of light as it passes from one medium to another.

• Dependent upon– Change in light wave speed– Change in direction

• Bending means an abrupt change in direction.

The extent to which the water waves bend depends on the size of the opening.

31.1 Diffraction and Huygens’ Principle

Interference patterns occur when waves from different sources arrive at the same point—at the same time.

25.7 Interference

a. In constructive interference, the waves reinforce each other to produce a wave of increased amplitude.

25.7 Interference

Amplitude has doubled in height

a. In constructive interference, the waves reinforce each other to produce a wave of increased amplitude.

b. In destructive interference, the waves cancel each other and no wave is produced.

25.7 Interference

INTERFERENCE

• The combination of two or more waves that exist in the same place at the same time.

• Constructive Interference (additive effect—in phase)• Destructive Interference (subtractive effect—out of

phase)• http://www2.biglobe.ne.jp/%7Enorimari/science/Jav

aEd/e-wave3.html• http://www2.biglobe.ne.jp/%7Enorimari/science/Jav

aEd/e-wave2.html

Light and colors

• Primary colors of light• Red-green-blue

What is color?

• When we see color, we are seeing specific frequencies of visible light

• VISIBLE LIGHT IS ROYGBIV• Red, orange, yellow, green, blue, indigo and violet• For visible light

– Red has the lowest frequency and longest wavelength– Violet has the highest frequency and shortest wavelength

Isaac Newton—discovered that white light is composed of seven different colors of light

White Light

Red

Orange

Yellow

Green

Blue

Indigo

Violet

A prism disperses white light into its primary frequencies of color

a. This square reflects all the colors illuminating it. In sunlight, it is white. When illuminated with blue light, it is blue.

b. This square absorbs all the colors illuminating it. In sunlight it is warmer than the white square.

28.2 Color by Reflection

Electricity

• More electrons than protons

• Negatively charged

• More protons than electrons

• Positively charged

Voltage

• Force that causes charges to move (the push or the electric field)

• Voltage exists if there is a potential difference in charges (negatively charged vs. positively charged)

• SI unit is Volt (V)

Electric Current

• The flow of charged particles.• Charges move from a position of higher to

lower electric PE (or higher voltage to lower voltage).

• SI unit is ampere (A or amps)

Resistance

• Resistance restricts the flow of electric charges.

• The cause: internal friction as moving charged particles collide.

• Unit for resistance is ohm

Series circuit Parallel circuit

http://iss.cet.edu/electricity/pages/a17.xml

Match statements with the correct circuit

• Series circuit vs. Parallel circuit

1. other bulbs go out if one bulb burns out 2. bulbs maintain same brightness if more bulbs are

added 3. two or more paths for electric current to flow4. bulbs dim if more bulbs are added 5. other bulbs stay lit if one bulb goes out 6. only one path for electric current to flow

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