THE ELECTROMAGNETIC SPECTRUM AND PHOTOELECTRIC EFFECT

THE ELECTROMAGNETIC SPECTRUM Quantum theory is based on how electrons

interact with electromagnetic waves. Electromagnetic waves are always present.

Some are completely safe and some are dangerous. Light Radio Microwave Gamma

THE EM SPECTRUM

RADIO WAVES Longest wavelength, lowest frequency. Information is carried by changing a property

of the wave. AM means Amplitude modulation FM means frequency modulation

Energy of one photon of a radio wave cannot remove electrons, so they are not considered to be dangerous.

MICROWAVES Called microwaves because they have a

wavelength of a micrometer. Used by many cell phones and wireless

devices to transmit information. Used in microwave ovens to heat food.

Heat polar molecules the best. Energy is not high enough to remove

electrons so they are considered to be safe.

INFRARED RADIATION The energy we lose as heat leaves our bodies by

infrared radiation.

VISIBLE LIGHT ROY G BIV

Red Orange Yellow Green Blue Indigo Violet

ULTRAVIOLET (UV) Part of Sunlight Can Cause DNA damage which may lead to

cancer. UV exposure causes increased aging by

damaging collagen. Melanin is the pigment that makes you look

tan and is produced by your skin to try and reflect UV rays

Sunscreen can block UV rays. SPF tells you how powerful the protection is.

X RAYS Used in medicine

Cannot travel through bones Given contrast to see other systems

Continued exposure can damage DNA and lead to increased cancer rates.

GAMMA RAYS Radioactive Decay They WILL cause cancer by mutating your

genes “CyberKnife” uses them to remove tumors. Used to treat and kill cancer cells.

“Radiation” = Gamma Rays

PHOTOELECTRIC EFFECT

IT ALL STARTS WITH WAVES… Electromagnetic rays hit an object (usually a

metal) and electrons are not just move up energy levels, they are released.

THEN COMES ELECTRICITY… The movement of the electrons causes the

metal to become a conductor of electricity It is a transformation of energy

From wave energy (EM Radiation) to electrical energy.

OTHER REQUIREMENTS The wave has to be made of photons with

high enough energy to remove the electron. Minimum energy needed to remove an electron

is called the threshold frequency. If the photon is below the threshold

frequency in energy it doesn’t matter how much light you shine on the object, nothing will happen.

Energy of the photon can be calculated with Einstein’s equations.

WHEN DO WE USED THIS? Solar Panels

Light from the sun causes electrons to be released.

The movement of electrons causes electricity to be produced.