and then there was light James Clerk Maxwell

Properties of E & B fields • Coulomb’s law: E-field lines start on +

In equation form: E-field lines start on +charges & end on - charges B-field

Maxwell The previous equations, as written, are mathematically inconsistent with the conservation of electric

Maxwell’s equations B-fields are produced by changing E-fields

Fields from an electric charge E x E Is the change in E instantaneous?

fun in the bathtub Water level will increase but not instantaneously 1 st waves

According to Maxwell’s eqs: E x E The change in E is not instantaneous

Wave solutions to Maxwell’s Eqs: Wave speed = = = 2 k k 2

“…let there be light. ” Maxwell’s equations have solutions that are waves of oscillating

Light wave B-field + E-field wave velocity

Visible light: Red Green Violet g-rays X-rays Ultraviolet Infrared micro waves TV/FM AM radio

Slides: 16

Download presentation

“…and then there was light. ” James Clerk Maxwell Physics 100 Chapt 16

Properties of E & B fields • Coulomb’s law: E-field lines start on + charge & end on – charge • Ampere’s law: B-fields are produced by electric currents • Faraday’s law: Changing B-fields produce E-fields • (un-named law): B-field lines never end

In equation form: E-field lines start on +charges & end on - charges B-field lines never end E-fields are produced by changing B fields B-fields are produced by electric currents

Maxwell The previous equations, as written, are mathematically inconsistent with the conservation of electric charge. He found he could fix this by adding one more term: B-fields are produced by changing E-fields

Maxwell’s equations B-fields are produced by changing E-fields

Fields from an electric charge E x E Is the change in E instantaneous? Does it occur only after some time? + M. E. s can tell us? +

fun in the bathtub Water level will increase but not instantaneously 1 st waves will propagate from her entrance point to the edge of the tub

According to Maxwell’s eqs: E x E The change in E is not instantaneous 1 st waves made of Efields & B-fields propagate thru space. + +

Wave solutions to Maxwell’s Eqs: Wave speed = = = 2 k k 2 x 9 x 109 Nm 2/C 2 2 x 10 -7 N/A 2 k ”strength” of electric force q 1 q 2 F c = k r 2 k = 9. 0 x 109 Nm 2/C 2 9 x 109+7(m 2/C 2)x. A 2 k ”strength” of ! magnetic force ! t h g i 16 2 2 l = 9 x 10 m /s f o I 1 I 2 l d F = k M e d e p 8 S = 3 x 10 m/s N -7 k = 2 x 10 A 2

“…let there be light. ” Maxwell’s equations have solutions that are waves of oscillating E- & B-fields that travel at the speed of light. Faraday & Maxwell made the immediate (& correct) inference that these waves are, in fact, light waves.

EM waves + + + -

antenna E B

Light wave B-field + E-field wave velocity

Light wave animation E B

Visible light: Red Green Violet g-rays X-rays Ultraviolet Infrared micro waves TV/FM AM radio waves Electro-magnetic “spectrum” l 0. 75 x 10 -6 m 0. 55 x 10 -6 m 0. 4 x 10 -6 m freq (c/l) 4. 0 x 1014 Hz 5. 5 x 1014 Hz 7. 5 x 1014 Hz