Identify the main regions of solar radiation
Recognise infrared, visible light and ultraviolet as the main regions carrying solar radiation.
Section 6.2.1 · The Sun as a star
Exam scope and assessment notes
Core and Extended · Physics 0972, 2026–2028. Use supplied distances, periods and stated orbital models. Drawings are not to scale. Written practice is self-checked. Human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall electromagnetic regions.
- Distinguish wavelength from brightness.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Can electromagnetic radiation cross a vacuum?
What you will learn
- Recognise infrared, visible light and ultraviolet as the main regions carrying solar radiation.
- Distinguish emitted radiation from what an eye or filtered detector records.
Follow the radiation beyond visible light
The Sun emits across an electromagnetic spectrum. Most of its radiated energy is in infrared, visible light and ultraviolet. Visible light is only the part our eyes detect; absence from an ordinary photograph does not establish absence of infrared or ultraviolet.
From longer to shorter wavelength, these three regions are infrared, visible and ultraviolet. They are electromagnetic waves and can travel through vacuum. They are not sound carried from the Sun through interplanetary air.
Read the stated measurement boundary
A detector records the radiation within its sensitivity and filters. A visible-only sensor cannot establish the Sun’s total emission across all regions. A supplied radiation table may be added only when its entries describe non-overlapping bands over the same interval.
“Most energy in these regions” does not assert equal energy in each region, nor exactly zero radiation elsewhere. A diagram identifying regions is not a measured distribution. Do not stare at the Sun or use an unfiltered optical instrument; these tasks use supplied data.
Pause and explain
Which three regions carry most solar radiation?
Worked example
An illustrative non-overlapping table gives infrared 42 units, visible 49, ultraviolet 8 and other regions 1. What do the three named regions total?
Show the worked solution
- Use the same supplied interval and unit.
- Add 42 + 49 + 8.
- Compare 99 with the total 100.
Answer 99 units out of 100 in this illustrative table.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Order infrared, ultraviolet and visible from longer to shorter wavelength.
Give me a hint
Place visible between its adjacent non-visible regions.
Compare my reasoning
- Infrared has longer wavelengths than visible.
- Ultraviolet has shorter wavelengths than visible.
- Combine the two comparisons.
Infrared, visible, ultraviolet.
Look for these in your work
- State the requested direction.
- Keep all three regions.
A visible-only camera records a bright Sun image. Can it show infrared is absent?
Give me a hint
Check the camera’s specified detection band.
Compare my reasoning
- It detects visible radiation.
- It excludes infrared from this measurement.
- A missing signal outside its band is not an absence measurement.
No; an infrared-sensitive measurement is needed.
Look for these in your work
- Identify the detector limit.
- Avoid inferring absence from filtering.
A teaching table gives IR 36 J, visible 50 J, UV 12 J and other 2 J in one interval. Evaluate “all energy is visible”.
Give me a hint
Add the non-overlapping entries before comparing shares.
Compare my reasoning
- Total = 100 J.
- Visible = 50 J, not the whole total.
- The three main regions sum to 98 J.
Visible is 50 J of 100 J; IR + visible + UV total 98 J.
Look for these in your work
- Preserve the supplied-data boundary.
- Distinguish most from all.
Common mistakes
- Visible is not the whole spectrum.
- Band labels do not assert equal energy shares.
- These exercises do not require direct Sun viewing.
What can you explain now?
Which three regions carry most solar radiation?
Compare with the explanation
Infrared, visible and ultraviolet
These are the three required main regions, without asserting equal shares.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Distinguish emitted radiation from what an eye or filtered detector records.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.