A-Level Physics Specification

OCR A H556

Section 5.5.2: Electromagnetic radiation from stars

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#5.5.2a

energy levels of electrons in isolated gas atoms

#5.5.2b

the idea that energy levels have negative values

#5.5.2c

emission spectral lines from hot gases in terms of emission of photons and transition of electrons between discrete energy levels

#5.5.2d

the equations hf=ΔEhf = ΔE and hcλ=ΔE\dfrac{hc}{λ} = ΔE

Learners will also require knowledge of section 4.5

#5.5.2e

different atoms have different spectral lines which can be used to identify elements within stars

#5.5.2f

continuous spectrum, emission line spectrum and absorption line spectrum

#5.5.2g

transmission diffraction grating used to determine the wavelength of light

The structure and use of an optical spectrometer are not required;
PAG 5

#5.5.2h

the condition for maxima dsinθ=nλd\sin{θ} = nλ, where d is the grating spacing

Proof of this equation is not required.

#5.5.2i

use of Wien’s displacement law λmax1Tλ_{max} ∝ \dfrac{1}{T} to estimate the peak surface temperature (of a star)

#5.5.2j

luminosity L of a star;
Stefan’s law L=4πr2σT4L = 4πr^2σT^4 where σ is the Stefan constant

Learners will also require knowledge of 4.4.1

#5.5.2k

use of Wien’s displacement law and Stefan’s law to estimate the radius of a star.