Introduction to Physical Science

Monday, Wednesday, Thursday

Tom Burbinetomburbine@astro.umass.edu

Quiz on Thursday

• Magnetism• Waves• Light• c = λ*f • E = h*f• Electromagnetic spctrum• Doppler shift

Wave

• Something that vibrates in space and time• Light acts as a wave• Sound acts as a wave

Frequency• The number of vibrations per unit time

Light

• Light is a form of energy

Light

• These are all forms of light– Gamma rays– X-rays– Ultraviolet light– Visible light– Infrared light– Radio waves

Light

• Can act as a particle• Can also act as a wave

Particle aspect

• Particles called photons stream from the Sun and can be blocked by your body

Photons

• Light is quantized• Comes in discrete packets called photons

Wave aspect

Thomas Young Experiment

• http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/

Characteristics of waves• velocity = wavelength x frequency• Wavelength = distance• Frequency = cycles per second = hertz

3 x 108 m/s

Speed of sound

• Speed of sound = 340 m / s

For light

• c = wavelength x frequency• In vacuum, speed of light stays the same• So if wavelength goes up• Frequency does down• f = frequency• λ = wavelength• c = λ x f

Calculations

• c = λ x f• So if the wavelength is 1 x 10-12 m• 3 x 108 m/s = 1 x 10-12 m * f• f = 3 x 108 m/s/1 x 10-12 m • f = 3 x 1020 s-1 = 3 x 1020 Hz

Calculations

• c = λ x f• So if the frequency is 1 x 1015 Hz• 3 x 108 m/s = λ * 1 x 1015 Hz • λ = 3 x 108 m/s/1 x 1015 Hz • λ = 3 x 10-7 m

Energy of light

• Energy is directly proportional to the frequency• E = h * f• h = Planck’s constant = 6.626 x 10-34 J/s• since f = c/λ• Energy is inversely proportional to the wavelength• E = hc/λ

Higher the frequency, Higher the energy of the photonHigher the wavelength, Lower the energy of the photon

Calculations

• What is the energy of a radio wave with a frequency of 1 x 107 Hz?

• E = h * f• h = Planck’s constant = 6.626 x 10-34 J/s• E = 6.626 x 10-34 J/s * 1 x 107

• E = 6.626 x 10-27 J

Calculations

• What is the energy of a gamma ray photon with wavelength of 1 x 10-15 m

• E = hc/λ• h = Planck’s constant = 6.626 x 10-34 J/s• E = 6.626 x 10-34 J/s * 3 x 108 m/s / 1 x 10-15 m• E = 1.99 x 10-10 J

So why are some types of radiation dangerous?

• Higher the energy, the farther the photons can penetrate

• So gamma and X-rays can pass much more easily into your the body

• These high-energy photons can ionize atoms in cells

• Ionization means removes electrons from an atom

More dangerous

http://www.arpansa.gov.au/images/basics/emr.jpg

ROYGBIV

• ROYGBIV • Red – long wavelength• Violet – short wavelength

Doppler Shift

• If a light or sound source moves towards you, the wavelength you measure (hear) from the source decreases– Frequency increases

• If a light or sound source moves away from you, the wavelength you measure (hear) from the source increases– Frequency decreases

• http://www.youtube.com/watch?v=-t63xYSgmKE&feature=related

Doppler Shift

http://www.psi.edu/~esquerdo/asp/shifts.jpg

• http://www.youtube.com/watch?v=a3RfULw7aAY

http://www.psi.edu/~esquerdo/asp/method.html

Wavelength

Any Questions?