Checkpoint 1 assesses L01, L02, L09 in the published syllabus sequence.
Assessment is drawn only from this lesson’s repaired effective pool.
Assessment is drawn only from this lesson’s repaired effective pool.
Assessment is drawn only from this lesson’s repaired effective pool.
This checkpoint assesses L01, L02, L09 only. Lesson file IDs remain stable; displayed lesson numbers follow the module’s syllabus sequence.
1. In the electromagnetic spectrum, which radiation has the longest wavelength?
2. The speed of light in a vacuum is approximately...
3. Light from the Sun reaches Earth across 150 million km of near-empty space. What does an electromagnetic wave need in order to make that journey?
4. James Clerk Maxwell showed that light is...
5. The order of the electromagnetic spectrum from lowest to highest frequency is...
6. Electromagnetic waves are produced whenever electric charges are:
7. In an electromagnetic wave travelling through a vacuum, the electric field and the magnetic field are oriented:
8. A beam of light passes from air into a block of glass and refracts. Which statement correctly describes what happens to the wave?
9. X-rays are produced when high-energy electrons undergo:
10. A point source emits 150 W of electromagnetic radiation uniformly in all directions. What is the intensity at a distance of 5.0 m from the source?
11. An emission spectrum consists of...
12. An absorption spectrum is produced when...
13. The Doppler effect for light from a source moving AWAY from an observer causes...
14. Astronomers use spectroscopy to determine the composition of stars by...
15. The Fraunhofer lines in the solar spectrum are...
SA1. State the general wave equation and its vacuum form. A 100 MHz radio wave travels in vacuum. Calculate its wavelength. (4 marks)
SA2. Explain how an accelerating charge produces an electromagnetic wave and state the relative directions of $\vec E$, $\vec B$ and propagation for a plane wave in vacuum. (4 marks)
SA3. An ideal isotropic source radiates 200 W. Calculate the intensity 5.0 m away and state two conditions required for $I=P/(4\pi r^2)$. (4 marks)
SA4. The H$\alpha$ line has rest wavelength 656.3 nm and is observed at 662.9 nm. Use the low-speed Doppler approximation to find the radial velocity and direction. (4 marks)
SA5. Explain what emission and absorption lines reveal about an astronomical source, and identify one instrumental limitation. (4 marks)
For any wave, $v=f\lambda$. In vacuum an electromagnetic wave has $v=c=3.00\times10^8$ m/s, so $\lambda=c/f=(3.00\times10^8)/(1.00\times10^8)=3.00$ m.
An accelerating charge produces changing electric and magnetic fields. Maxwell’s equations couple those changing fields so the disturbance propagates. For a plane wave in vacuum, $\vec E$ and $\vec B$ are perpendicular to one another and both are perpendicular to the propagation direction; their amplitudes satisfy $E_0/B_0=c$.
$I=200/[4\pi(5.0)^2]=0.64$ W m$^{-2}$. The relation assumes spherical spreading from an effectively point-like source with radiated power distributed uniformly and negligible absorption; $r$ must be measured from the source.
$\Delta\lambda=+6.6$ nm, so $v/c\approx\Delta\lambda/\lambda_0=6.6/656.3$. Thus $v\approx3.0\times10^6$ m s$^{-1}$. The positive shift is a redshift, so the source is receding.
Line wavelengths identify atomic or ionic species because they correspond to energy-level differences. Shifts give radial motion, while line strengths and ionisation states constrain temperature and composition. Finite spectral resolution can blend nearby lines; calibration error can shift the wavelength scale.