Physics trip: Monday 8 th April Need payment and permission slips back by Friday Reminder: internal – last week of term Tasks to complete:  homework and old exam questions (nuclear and photo-electric effect) We have one more topic to cover before the internal: atomic spectra  homework set and old exam questions for this also

Student feedback: H/W books Textbook work Do now / starter activities Revision booklets Worksheets Playing with the diffraction grating and lasers Doppler applications (speed radar, expansion of the universe) Estimating and processing uncertainties Experiment 1: measuring standing waves with ticker timers Experiment 2: measuring the wavelength of a laser using a diffraction grating Video clips Phet animations Ruben tube demo Mini tests Do the sticker timeline

Notes on Bohr’s model

photons of white light (all frequencies) shone through a sample of gas most frequencies pass straight through but some are absorbed and re-emitted (in random directions) Absorption spectrum: dark lines indicate the “missing” frequencies (the absorbed photons) Where would you place the spectrometer to detect the emitted photons? (the emission spectrum)

The Hydrogen Spectrum Lyman Series S=1 (UV) Balmer Series S=2 (visible) Paschen Series S=3 (IR) Bracket Series S=4 (IR) Pfund Series S=5 (IR) Nucleus Shell no. / Energy level

The Hydrogen Spectrum The wavelengths of the emitted photons are given by: The wavelengths of the emitted photons are given by: R=Rydberg’s Constant=1.097x10 7 m -1 R=Rydberg’s Constant=1.097x10 7 m -1 S=Series no. (the shell jumped into) S=Series no. (the shell jumped into) L=Line no. (the shell jumped from) L=Line no. (the shell jumped from)

Bohr’s Model of the Atom The energy levels in the Hydrogen atom are given by : The energy levels in the Hydrogen atom are given by : h=Plancks constant = 6.63x Js h=Plancks constant = 6.63x Js c=speed of light = 3x10 8 ms -1 c=speed of light = 3x10 8 ms -1 R=Rydbergs constant = 1.097x10 7 m -1 R=Rydbergs constant = 1.097x10 7 m -1 n=energy level = 1,2,3,4…… (quantum number) n=energy level = 1,2,3,4…… (quantum number)

Bohr’s Model of the Atom -2 Energy (x J) 0 n=1 n=2 n=3 n=4 n=∞

Questions 1)Calculate the wavelength and frequency of the first line in the Balmer series 2)An electron in a hydrogen atom falls from the third to the second energy level a) How much energy does the electron lose? b) What is the energy of the photon emitted? c) What is the frequency of the emitted photon? textbook p182 textbook p187