Waves & photons

Waves & photons

Transverse (top) and Standing wave longitudiinal waves

Waves & photons What can be measured? λ λ

meters: 0.0 3.0 6.0 Sec: 0.0 0.5 1.0

Frequency (f = 2 hertz): Complete waves in 1.0 sec:

Wavelength (λ= 3.0 m): Linear distance between repetitions:

Period (T = 0.5 sec): Time to complete 1.0 wavelength (λ). NOTE: f = 1/T

wave velocity: c = Δ x/Δ t = 3.0 m/0.5 t = 6.0 m/sec or 6.0 m/1.0 sec =6.0 m/sec

NOTE: c = f λ = 2 hz X 3.0 m = 6.0 m/sec

c

Waves & photons-Photoelectric effect

Wave particle duality: The wave model explains some properties of light such as diffraction. The particle (photon) model explains other experiments such as the photoelectric effect. One model is used at the exclusion of the other model.

Particle property (energy) is related to the corresponding wave property(frequency): E = hf h = 6.63 X 10-34 j-sec

Waves & photonsProblems: c = 3.00 X 108 m/s h = 6.63 X 10-34 j-s 1.0 nm = 1.0 X 10-9 m

A microwave oven emits a 2450 Mhz (2450 X 106 hz)wave.

1. Calculate the wavelength (m) of this wave. ANS: 0.122 m

2. Calculate the wavelength (nm). ANS: 1.22 X 108 nm

3. Calculate the energy of each photon. ANS: 1.62 X 10 -24 j

4. Each photon is a particle (package) carrying 1.62 X 10-24 j.Calculate the number of photons needed to heat 1 cup (225g)of water (c = 4.18 j/g-oC) from 25oC to 100OC. [ΔH = 70500j] ANS: 4.35 X 1028 photons

Waves & photons( Spectra)Continous sprectrum.

c = 3.00 X 108 m/s h = 6.63 X 10-34 j-s 1.0 nm = 1.0 X 10-9 m

1. Calculate the frequency of a green (λ = 486 nm) wave. ANS: 6.17 X 1014 hz

2. Calculate the energy of a red hydrogen photon (λ = 660 nm). ANS: 3.01 X 10-19 j

3. Calculate the photon energy of the shortest wavelength (λ = 490 nm) sodium spectral line. ANS: 4.06 X 10-19 j

Waves & photons c = 3.00 X 108 m/s h = 6.63 X 10-34 j-s 1.0 nm = 1.0 X 10-9 m

WJJD (AM radio) transmits 7.69 X 10-28 j photons. AM radio operates in the kilohertz range.

1. Calculate WJJD’s transmitting frequency. ANS: 1.16 X 106 hz The AMradio dial shows the frequency in khz. What is the radio dial setting forWJJD? ANS: 1160

2. Calculate the wavelength of the WJJD wave. ANS: 2.59 X 102 m

College of Dupage operates radio station WCDB (90.9 FM = 90.9 X 106 hz).

3. Calculate the wavelength of the wave in nm. ANS: 3.30 X 109 nm

4. Calculate the energy of a WCDB photon. ANS: 6.03 X 10-26 j

Waves & photons c = 3.00 X 108 m/s h = 6.63 X 10-34 j-s 1.0 nm = 1.0 X 10-9 mCobalt-60 is used to treat cancer. Cobalt-60 emits gamma photons at anenergy of 1.33 Mev (2.13 X 10-13 j).

1. Calculate the wave frequency. ANS: 3.21 X 1020 hz

2. Calculate the wavelength of the wave in nm. ANS: 9.35 X 10-4 nm

A police K band radar gun beams a 22.2 ghz microwave (1.0 ghz = 1.0 X109 hz )at a car. The Doppler effect produces a reflected wave with a slightly longer or shorter wavelength. The reflected photon will have less or more energy. The reflected wave or the photon can indicate the automobile's speed.

3. Calculate the wavelength of the beamed wave in nm. [0.0135m] ANS: 1.35 X 107 nm

4. Calculate the energy of the beamed photon. ANS: 1.47 X 10-23j

Waves & photons1. DNA uses RNA polymerase (enzyme) to form RNA which then forms protein. The protein is exposed to green light (λ = 550nm). Calculate the photon energy of green light. h=6.63 X10-34 j –s c=3.00 X108 m/s [ANS: 218 kj/mol]

2. Which bonds can be destroyed by green light? [ANS: None]

Bond Bond energy Bond Bond energy Bond Bond energy

C-C 347 kj/mol C=O 736 kj/mol C-S 259 kj/mol

C-N 305 kj/mol C-O 360 kj/mol C-H 414 kj/mol

N-H 389 kj/mol H-O 464 kj/mol

Waves & photons

DNA uses RNA polymerase (enzyme) to form RNA which then forms protein. 1. The protein is exposed to uv-A (λ = 360nm). Calculate the photon energy of uv-A. h=6.63 X10-34 j –s c=3.00 X108 m/s [ANS: 333 kj/mol]

Bond Bond energy Bond Bond energy Bond Bond energy

C-C 347 kj/mol C=O 736 kj/mol C-S 259 kj/mol

C-N 305 kj/mol C-O 360 kj/mol C-H 414 kj/mol

N-H 389 kj/mol H-O 464 kj/mol

2. Which bonds can be destroyed by uv-A light? ANS: [C-S, C-N bonds]

Waves & photons

DNA uses RNA polymerase (enzyme) to form RNA which then forms protein. 1. The protein is exposed to uv-B (λ = 300nm). Calculate the photon energy of uv-B. h=6.63 X10-34 j –s c=3.00 X108 m/s [ANS: 399 kj/mol]

Bond Bond energy Bond Bond energy Bond Bond energy

C-C 347 kj/mol C=O 736 kj/mol C-S 259 kj/mol

C-N 305 kj/mol C-O 360 kj/mol C-H 414 kj/mol

N-H 389 kj/mol H-O 464 kj/mol

2. Which bonds can be destroyed by uv-B light? [C-C, C-N, N-H, C-O, C-S]

Waves & photons

NOTE: 1.0 X 10-9nm = 1.0 m Example: 4 X 10-7 m = 400 nm

What other kinds of EM waves will break chemical bonds?

uv-B uv-A