CH 301 1.1 - 1.5 Quiz Review

Ranking of EMR

Radio waves, microwaves, IR, visible light, UV, x-ray, gamma rays

Radio waves

• Excites spin of nucleus

• Used for MRI

• AM and FM

Microwaves

• Excites spin of electrons

• Excites rotation of H2O and fats around 12 cm to cook food

Infrared

• Causes vibrations in molecules

• Used in night vision of goggles

• Excites wavelengths of -OH in ethanol, used to measure intoxication

Visible Light

• 300 to 800 nm

• Excites valence electrons to higher energy level

• Solution for H-atom (Balmer series)

• Rays of detection for human eye

UV

• Excites valence electrons

• Lyman series for H emission

• Causes sunburns

X-ray

• Excites core electrons

• Used in medicine for invasive imaging

• Causes sun burn

Gamma ray

• Associated with decay of atom nucleus

• Are emitted from stars, hence cosmic ray name

Photoelectric Effect Theory

When light shines on a metal surface, it can cause electrons to be ejected

• Photon has to meet or exceed the threshold energy (work function)

Threshold energy (work function)

The minimum energy required to eject an electron from a metal surface when illuminated by light.

• Unique to each metal

Kinetic energy from the ejected electron

KE is released from the ejected electron if the photon has more energy than required

Increase energy by

• Increasing frequency

• Decreasing wavelength

Equation for energy

E = hv = Ethreshold + KE

What does the photoelectric effect show?

Light behaves as particles, not just waves

What happens if the photon’s energy is lower than the work function?

No photon electron is ejected