Explain how the invention of charge-coupled devices (CCDs) improved astronomical observations compared with using photographic film.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
CCDs are far more sensitive to light than photographic film, giving a higher signal for the same exposure.
They can detect a wider range of wavelengths, including infrared and ultraviolet, which film cannot.
CCDs produce a digital image that can be stored electronically and processed by a computer.
Their quantum efficiency is higher, so they record a larger proportion of incident photons.
Consequently, shorter exposure times are required and fainter or more distant objects can be imaged.
They can detect a wider range of wavelengths, including infrared and ultraviolet, which film cannot.
CCDs produce a digital image that can be stored electronically and processed by a computer.
Their quantum efficiency is higher, so they record a larger proportion of incident photons.
Consequently, shorter exposure times are required and fainter or more distant objects can be imaged.
Examiner tips
- Use the word ‘sensitivity’ and ‘quantum efficiency’ to hit the key terms.
- Mention the wider wavelength range and digital storage to cover all points.
- Show how higher sensitivity leads to shorter exposures and fainter targets.
Common mistakes
- Confusing CCDs with CCD cameras; forgetting the digital aspect.
- Overlooking the wider wavelength range or the higher quantum efficiency.
- Not linking higher sensitivity to shorter exposure times or fainter objects.
Mark scheme (5 marks)
- CCDs are more sensitive to light than photographic film
- CCDs can detect a greater range of wavelengths / frequencies (including infrared and ultraviolet) compared with photographic film
- CCDs produce a digital (electronic) image that can be stored and processed by a computer
- CCDs are more efficient / have a higher quantum efficiency — they record a higher proportion of the light that falls on them compared with photographic film
- This means shorter exposure times are needed / fainter or more distant objects can be imaged
Key terms in this question
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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