Light … is an electromagnetic wave:Light … is an electromagnetic wave: • … is a wave pattern of electric and magnetic fields• … propagates in vacuum• … has wavelength (blue: 400 nm, red: 700 nm)

The physics of light

1 mm = millimeter

1000 m = 1 mm

1000 nm = 1 m

Micrometer(size of a germ)

Nanometer(size of ten atoms)

LearnLearnunits of distance!units of distance!

0.4 m 0.7 m Millimeter

(size of ant)

Olaf Römer

Speed of light c = 300,000 km/s: Discovered by: Olaus Roemer (1675)

• Eclipses of Jupiter’s moons come a few minutes late when Jupiter is on the far side of its orbit.• Reason: light needs extra time to reach us.• Conclusion: light needs 9 minutes to traverse the Sun-Earth distance.

Watch07JupiterMoonDance.mov

Light takesLight takes • a few minutes/hours to move around in the solar system• years or more to go from star to star

The electromagnetic spectrum

Light has a wavelength:

Wavelength of light means color:

• Blue has short wavelength• Red has long wavelength

What isbeyond blue?

Bluer than blue is UV (ultraviolet) - even shorter wavelengthRedder than red is IR (infrared) - even longer wavelength

These are colors of light invisible to the eye.

The full spectrum

And what is beyond those wavelengths?And what is beyond those wavelengths?

(A prism breaks up white light into colors.)

They all move with the same speed c = 300,000 km/s

Radio | Infrared | Visible | Ultraviolet X-ray| -ray

Need spacecraft(Far UV, X-ray, -ray)

Need spacecraft

Eye / TelescopeRadio antenna

PrismSlit

White light

Questions coming …

sec

30Question 11 29Which one is moving fastest?

A Radio waves

B X-rays

C Visible light

D Laser

E The same

28272625242322212019181716151413121110 9 8 7 6 5 4 3 2 1 0

Next question coming …

sec

30Question 12 29What is the difference between red and blue light?

A Intensity.

B Speed.

C Wavelength.

D Blue is composite, red is not.

E Red is existence of light, blue is lack of light.

28272625242322212019181716151413121110 9 8 7 6 5 4 3 2 1 0

Next question coming …

sec

45Question 13 403530252019181716151413121110 9 8 7 6 5 4 3 2 1 0

Next question coming …

How many of the following types of “light” penetrates the atmosphere?

• Radio waves • Far IR • Regular light • Far UV • X-rays

A 1 B 2 C 3 D 4 E 5

sec

30Question 14 29How was the speed of light measured for the first time?

A In an experiment with a laser beam.

B By the time delay the astronauts’ answer came from the Moon.

C Observing the moons of Jupiter.

D By measuring the radar signal reflected by the Moon.

E By measuring the time light takes to arrive to usfrom another galaxy.

28272625242322212019181716151413121110 9 8 7 6 5 4 3 2 1 0

Structure of atom

Recall: Chemistry cannot change the nucleus, only bind atoms into molecules

Isotopes: same number of p and e, different n. Same chemical properties.

Examples: H: 1 p 0 n 1 eDeutron: 1 p 1 n 1 e (same as H but heavier)

He: 2 p 2 n 2 e