Class 10th Science Chapter 10 – The Human Eye and the Colourful World | Formation of Rainbow

The Human Eye and the Colourful World

Formation of Rainbow | इन्द्रधनुष का निर्माण

Class 10 Science | CBSE + Foundation + Competitive

🌈 Formation of Rainbow | इन्द्रधनुष का निर्माण

1. Introduction | परिचय

A rainbow is a natural optical phenomenon in which sunlight appears as a multicoloured arc in the sky after or during rainfall when sunlight interacts with water droplets.

इन्द्रधनुष एक प्राकृतिक प्रकाशीय घटना है जिसमें वर्षा के बाद या वर्षा के दौरान सूर्य का प्रकाश जल की बूंदों से परस्पर क्रिया करके आकाश में बहुरंगी चाप के रूप में दिखाई देता है।

The formation of a primary rainbow mainly involves three important optical processes:

1. Refraction – अपवर्तन

2. Dispersion – विक्षेपण

3. Internal Reflection – आंतरिक परावर्तन

2. Principle of Rainbow Formation | इन्द्रधनुष बनने का सिद्धांत

When sunlight enters a spherical water droplet, it is refracted and dispersed into different colours. The separated light undergoes internal reflection inside the droplet and is refracted again when it emerges.

जब सूर्य का प्रकाश गोलाकार जल की बूंद में प्रवेश करता है, तो उसका अपवर्तन और विक्षेपण होता है। अलग हुए रंग बूंद के अंदर आंतरिक परावर्तन करते हैं और बाहर निकलते समय पुनः अपवर्तित होते हैं।

Thus, the formation of a primary rainbow can be summarized as:

Refraction → Dispersion → Internal Reflection → Refraction

3. Formation of Rainbow in a Water Droplet | जल की बूंद में इन्द्रधनुष

4. Step-by-Step Formation | चरणबद्ध निर्माण

Step 1 – Refraction | चरण 1 – अपवर्तन

When sunlight enters a water droplet from air, it changes its speed and bends due to refraction.

जब सूर्य का प्रकाश वायु से जल की बूंद में प्रवेश करता है, तो उसकी चाल बदलती है और वह अपवर्तित होता है।

Step 2 – Dispersion | चरण 2 – विक्षेपण

White sunlight contains different wavelengths. Water has slightly different refractive indices for different wavelengths, so the colours are deviated by different amounts.

श्वेत सूर्यप्रकाश में विभिन्न तरंगदैर्ध्य के रंग होते हैं। जल का अपवर्तनांक अलग-अलग तरंगदैर्ध्य के लिए अलग होता है, इसलिए रंग अलग-अलग मात्रा में विचलित होते हैं।

Step 3 – Internal Reflection | चरण 3 – आंतरिक परावर्तन

The dispersed light reaches the opposite inner surface of the water droplet and undergoes internal reflection.

विक्षेपित प्रकाश बूंद की दूसरी आंतरिक सतह तक पहुँचता है और वहाँ आंतरिक परावर्तन करता है।

Step 4 – Refraction Again | चरण 4 – पुनः अपवर्तन

The reflected light emerges from the droplet and is refracted again. Different colours emerge in different directions.

परावर्तित प्रकाश बूंद से बाहर निकलते समय पुनः अपवर्तित होता है। अलग-अलग रंग अलग दिशाओं में निकलते हैं।

5. Primary Rainbow | प्राथमिक इन्द्रधनुष

A primary rainbow is formed mainly after one internal reflection inside a water droplet.

प्राथमिक इन्द्रधनुष जल की बूंद के अंदर मुख्यतः एक आंतरिक परावर्तन के बाद बनता है।

Primary Rainbow: One internal reflection.

प्राथमिक इन्द्रधनुष: एक आंतरिक परावर्तन।

In a primary rainbow, red is generally seen on the outer side and violet on the inner side of the arc.

प्राथमिक इन्द्रधनुष में सामान्यतः लाल रंग बाहरी भाग में और बैंगनी रंग आंतरिक भाग में दिखाई देता है।

6. Secondary Rainbow | द्वितीयक इन्द्रधनुष

A secondary rainbow is formed when light undergoes two internal reflections inside a water droplet before emerging.

द्वितीयक इन्द्रधनुष तब बनता है जब प्रकाश जल की बूंद के अंदर दो आंतरिक परावर्तन करता है।

Its colour order is reversed compared with the primary rainbow.

इसका रंग क्रम प्राथमिक इन्द्रधनुष की तुलना में उल्टा होता है।

Primary Rainbow	Secondary Rainbow
One internal reflection	Two internal reflections
Brighter	Fainter
Red outer, violet inner	Violet outer, red inner
Smaller angular radius	Larger angular radius

7. Position of Rainbow | इन्द्रधनुष की स्थिति

A rainbow is usually seen when the observer has the Sun behind them and water droplets are present in the opposite part of the sky.

इन्द्रधनुष सामान्यतः तब दिखाई देता है जब सूर्य पर्यवेक्षक के पीछे हो और सामने के आकाश में जल की बूंदें मौजूद हों।

Memory Trick:

🌞 Sun Behind → Rainbow Ahead

सूर्य पीछे → इन्द्रधनुष सामने

8. Angular Position of Primary Rainbow | प्राथमिक इन्द्रधनुष का कोण

For a primary rainbow, the emerging rays reach the observer from a direction roughly 40°–42° from the antisolar direction, depending on colour and the observation conditions.

स्कूल स्तर पर प्राथमिक इन्द्रधनुष को सूर्य के विपरीत दिशा से लगभग 40°–42° के कोणीय क्षेत्र में देखा जाता है।

The approximate angular radius often quoted for the primary rainbow is about 42° for red light, with violet at a somewhat smaller angle.

9. Why Does a Rainbow Appear as an Arc? | इन्द्रधनुष चाप के रूप में क्यों?

A rainbow is formed by light emerging from many water droplets at suitable angles. From the observer's position, droplets satisfying the required geometry lie approximately on a cone around the line opposite the Sun. The intersection of this cone with the sky appears as an arc.

पर्यवेक्षक की स्थिति से उपयुक्त कोण पर प्रकाश भेजने वाली अनेक जल बूंदें एक शंकु जैसी ज्यामितीय व्यवस्था बनाती हैं। आकाश में इस व्यवस्था का भाग हमें चाप के रूप में दिखाई देता है।

10. Can a Rainbow Be a Complete Circle? | क्या इन्द्रधनुष पूरा वृत्त हो सकता है?

Yes. From an elevated position such as an aircraft, under suitable conditions, a rainbow may sometimes appear as a nearly complete circle. From the ground, the lower part is usually hidden below the horizon.

हाँ। विमान जैसी ऊँची स्थिति से उचित परिस्थितियों में इन्द्रधनुष लगभग पूर्ण वृत्त के रूप में दिखाई दे सकता है। भूमि से देखने पर इसका निचला भाग सामान्यतः क्षितिज के नीचे छिपा रहता है।

11. Colours of Rainbow | इन्द्रधनुष के रंग

Order	Colour	Relative Wavelength
1	Violet	Shortest
2	Indigo	Short
3	Blue	Short–medium
4	Green	Medium
5	Yellow	Medium–long
6	Orange	Long
7	Red	Longest

12. Role of Dispersion | विक्षेपण की भूमिका

Dispersion is essential for the formation of the colours of a rainbow. Without wavelength-dependent refraction, the colours would not separate in the same way.

इन्द्रधनुष में रंगों के अलग-अलग दिखाई देने के लिए विक्षेपण महत्वपूर्ण है। अलग-अलग तरंगदैर्ध्य के प्रकाश का अपवर्तन अलग-अलग मात्रा में होने के कारण रंग अलग होते हैं।

13. Role of Refraction | अपवर्तन की भूमिका

Refraction occurs when sunlight enters and leaves a water droplet. At these boundaries, the speed and direction of light change.

जल की बूंद में प्रकाश के प्रवेश और बाहर निकलने के समय अपवर्तन होता है। इस दौरान प्रकाश की चाल और दिशा बदलती है।

14. Role of Internal Reflection | आंतरिक परावर्तन की भूमिका

After entering the droplet and being dispersed, the light reaches the opposite surface and is internally reflected back towards the observer side.

विक्षेपण के बाद प्रकाश बूंद की दूसरी सतह तक पहुँचकर आंतरिक रूप से परावर्तित होता है और पर्यवेक्षक की दिशा में लौटता है।

15. Primary vs Secondary Rainbow | प्राथमिक और द्वितीयक इन्द्रधनुष

Feature	Primary Rainbow	Secondary Rainbow
Internal reflections	One	Two
Brightness	Brighter	Fainter
Colour order	Red outer, violet inner	Violet outer, red inner
Approximate radius	~42° for red	~51°–53°
Location	Closer to antisolar point	Outside primary rainbow

16. Double Rainbow | दोहरा इन्द्रधनुष

Sometimes both primary and secondary rainbows can be observed at the same time. The secondary rainbow appears outside the primary rainbow and is usually fainter.

कभी-कभी प्राथमिक और द्वितीयक दोनों इन्द्रधनुष एक साथ दिखाई दे सकते हैं। द्वितीयक इन्द्रधनुष प्राथमिक इन्द्रधनुष के बाहर और सामान्यतः अधिक हल्का दिखाई देता है।

17. Alexander's Dark Band | अलेक्जेंडर की डार्क बैंड

When both primary and secondary rainbows are visible, a relatively dark region may appear between them. This is called Alexander's dark band.

जब प्राथमिक और द्वितीयक इन्द्रधनुष दोनों दिखाई देते हैं, तो उनके बीच का क्षेत्र अपेक्षाकृत गहरा दिखाई दे सकता है। इसे Alexander's dark band कहा जाता है।

18. Why Is the Sun Behind the Observer? | सूर्य पीछे क्यों होता है?

For a primary rainbow, sunlight must enter droplets in front of the observer, undergo the required refraction, dispersion and internal reflection, and then return toward the observer. Therefore the Sun is on the opposite side of the sky.

प्राथमिक इन्द्रधनुष के लिए सूर्य का प्रकाश पर्यवेक्षक के सामने स्थित जल की बूंदों पर पड़ना चाहिए और परावर्तन के बाद पर्यवेक्षक की ओर लौटना चाहिए। इसलिए सूर्य पर्यवेक्षक के पीछे होता है।

19. Simple Demonstration of Rainbow | सरल प्रदर्शन

A rainbow-like spectrum can be demonstrated using a transparent glass prism or fine water spray under sunlight.

1. Stand with the Sun behind you.
2. Use a fine spray of water in front of you.
3. Observe the region opposite the Sun.
4. Under suitable conditions, coloured light may be visible.

यह प्रदर्शन केवल उपयुक्त प्रकाश, बूंदों और viewing geometry में स्पष्ट दिखाई देता है।

20. Important Relations | महत्वपूर्ण संबंध

v = νλ

μ = c/v

v = speed of light in the medium

ν = frequency

λ = wavelength

μ = refractive index

c = speed of light in vacuum

Exam Point:

Frequency of light does not change when light passes from one medium to another, whereas its speed and wavelength change.

21. 30 MCQs | बहुविकल्पीय प्रश्न

Q1. A rainbow is a:

(A) Natural optical phenomenon

(B) Chemical reaction

(C) Mechanical phenomenon

(D) Electrical phenomenon

Answer: A

Q2. Which three processes are mainly involved in primary rainbow formation?

(A) Reflection, absorption and diffraction

(B) Refraction, dispersion and internal reflection

(C) Diffraction, scattering and absorption

(D) Interference, reflection and absorption

Answer: B

Q3. The splitting of sunlight into colours inside a water droplet is called:

(A) Reflection

(B) Refraction

(C) Dispersion

(D) Absorption

Answer: C

Q4. In a primary rainbow, light undergoes:

(A) No internal reflection

(B) Three internal reflections

(C) Two internal reflections

(D) One internal reflection

Answer: D

Q5. In a primary rainbow, the outer colour is generally:

(A) Red

(B) Violet

(C) Blue

(D) Green

Answer: A

Q6. In a primary rainbow, violet is generally seen:

(A) Outside red

(B) On the inner side

(C) Above the Sun

(D) Nowhere

Answer: B

Q7. A secondary rainbow involves:

(A) No reflection

(B) One reflection

(C) Two internal reflections

(D) Only scattering

Answer: C

Q8. A secondary rainbow is generally:

(A) Brighter than primary

(B) Equal in brightness

(C) Invisible always

(D) Fainter than primary

Answer: D

Q9. For seeing a primary rainbow, the Sun is generally:

(A) Behind the observer

(B) Directly overhead only

(C) In front of the observer

(D) Below the ground

Answer: A

Q10. The approximate angular radius of the primary rainbow for red light is:

(A) 20°

(B) About 42°

(C) 90°

(D) 5°

Answer: B

Q11. The rainbow is formed by:

(A) Dust particles only

(B) Smoke only

(C) Water droplets

(D) Clouds only

Answer: C

Q12. Which colour has the longest wavelength?

(A) Violet

(B) Blue

(C) Green

(D) Red

Answer: D

Q13. Which colour has the shortest wavelength?

(A) Violet

(B) Red

(C) Yellow

(D) Orange

Answer: A

Q14. The colour order of the primary rainbow from outer to inner is:

(A) VIBGYOR

(B) ROYGBIV

(C) GYORVIB

(D) BIVGYOR

Answer: B

Q15. The secondary rainbow has colour order:

(A) Same as primary

(B) Random

(C) Reversed compared with primary

(D) Only red and violet

Answer: C

Q16. Which phenomenon causes separation of colours?

(A) Reflection

(B) Absorption

(C) Heating

(D) Dispersion

Answer: D

Q17. Internal reflection occurs inside:

(A) Water droplets

(B) Sun

(C) Air only

(D) Clouds only

Answer: A

Q18. The dark region between primary and secondary rainbows is called:

(A) Newton band

(B) Alexander's dark band

(C) Raman band

(D) Prism band

Answer: B

Q19. A primary rainbow is usually:

(A) Outside the secondary

(B) Below the ground

(C) Inside the secondary rainbow

(D) Above the Sun

Answer: C

Q20. The source of light responsible for a natural rainbow is:

(A) Moon only

(B) Stars

(C) Lightning

(D) Sun

Answer: D

Q21. A rainbow may appear after rainfall because the atmosphere contains:

(A) Water droplets

(B) Only dust

(C) Smoke

(D) Salt crystals only

Answer: A

Q22. Which process occurs when sunlight first enters a raindrop?

(A) Absorption only

(B) Refraction

(C) Reflection only

(D) Diffraction

Answer: B

Q23. The colours of rainbow arise because:

(A) Water is coloured

(B) Air is coloured

(C) Different wavelengths are refracted differently

(D) Sun emits only one colour

Answer: C

Q24. The secondary rainbow is located:

(A) Inside the primary

(B) At the Sun

(C) Underground

(D) Outside the primary

Answer: D

Q25. Which colour generally deviates least in water?

(A) Red

(B) Violet

(C) Blue

(D) Green

Answer: A

Q26. Which colour generally deviates most?

(A) Red

(B) Violet

(C) Yellow

(D) Orange

Answer: B

Q27. A complete circular rainbow is more likely to be observed:

(A) Underground

(B) Inside a closed room

(C) From an elevated position under suitable conditions

(D) At midnight always

Answer: C

Q28. The approximate angular radius of the secondary rainbow is:

(A) 10°

(B) 25°

(C) 35°

(D) About 51°–53°

Answer: D

Q29. The rainbow is an example of:

(A) Dispersion and reflection-related optical phenomena

(B) Chemical combustion

(C) Nuclear reaction

(D) Sound interference only

Answer: A

Q30. Which sequence best represents primary rainbow formation?

(A) Reflection → absorption → heating

(B) Refraction → dispersion → internal reflection → refraction

(C) Scattering → diffraction → absorption

(D) Heating → reflection → evaporation

Answer: B

22. 30 Subjective Questions with Answers | वर्णनात्मक प्रश्न

2 Marks Q1. What is a rainbow?

A rainbow is a natural optical phenomenon in which sunlight appears as a coloured arc due to its interaction with water droplets.

2 Marks Q2. Name the main phenomena involved in rainbow formation.

Refraction, dispersion and internal reflection are the main processes involved in the formation of a primary rainbow.

2 Marks Q3. What is a primary rainbow?

A primary rainbow is formed mainly after one internal reflection of light inside a water droplet.

2 Marks Q4. Why is a rainbow usually seen opposite the Sun?

Because the sunlight must enter water droplets in front of the observer, undergo internal reflection and emerge towards the observer.

2 Marks Q5. Which colour is seen on the outer side of a primary rainbow?

Red is generally seen on the outer side of a primary rainbow.

3 Marks Q6. Explain the role of refraction in rainbow formation.

Light is refracted when it enters and leaves a water droplet. This changes its direction and contributes to the angular separation required for the rainbow.

3 Marks Q7. What is the role of dispersion?

Different colours have different wavelengths and experience different refractive indices in water. Hence they are deviated by different amounts and become separated.

3 Marks Q8. What is internal reflection?

Internal reflection is the reflection of light back into a medium when light travelling inside the medium reaches its boundary under conditions suitable for internal reflection.

3 Marks Q9. Why does the Sun need to be behind the observer?

The sunlight must fall on water droplets in front of the observer and return towards the observer after internal reflection.

3 Marks Q10. Write the colour sequence of a primary rainbow.

From outer to inner: Red, Orange, Yellow, Green, Blue, Indigo and Violet.

4 Marks Q11. Explain the formation of a primary rainbow.

Sunlight enters a water droplet and is refracted and dispersed. The separated colours undergo one internal reflection and then emerge after another refraction. The observer sees the separated colours as a rainbow.

4 Marks Q12. Why is violet inside and red outside in a primary rainbow?

Different colours have different refractive indices and therefore different deviations in water. The resulting geometry places red at the outer edge and violet at the inner edge of the primary arc.

4 Marks Q13. What is the difference between primary and secondary rainbow?

A primary rainbow involves one internal reflection and is brighter, with red outside. A secondary rainbow involves two internal reflections, is fainter, and has reversed colour order.

4 Marks Q14. Why is the secondary rainbow fainter?

The light undergoes an additional internal reflection, so less light reaches the observer compared with the primary rainbow.

4 Marks Q15. What is Alexander's dark band?

It is the relatively dark region between the primary and secondary rainbows when both are visible.

5 Marks Q16. Describe rainbow formation step by step.

1. Sunlight enters the water droplet and is refracted. 2. White light is dispersed into colours. 3. The colours travel inside the droplet. 4. The light undergoes internal reflection. 5. The reflected colours leave the droplet after another refraction. 6. The observer sees the coloured arc.

5 Marks Q17. Explain why a rainbow has seven commonly identified colours.

White sunlight contains a continuous range of visible wavelengths. Due to dispersion, different wavelengths are separated. These colours are commonly grouped and named as VIBGYOR in school-level description.

5 Marks Q18. Explain the role of water droplets.

Water droplets act like tiny optical systems. They refract sunlight, disperse its colours, internally reflect the separated light and refract it again on emergence.

5 Marks Q19. Explain why rainbow is not visible whenever it rains.

Rain alone is not sufficient. Suitable positions of the Sun, observer and water droplets are required. Usually the Sun should be behind the observer and the droplets should be in the opposite part of the sky.

5 Marks Q20. Explain the approximate angular position of a primary rainbow.

The primary rainbow is seen at an angular radius of roughly 40°–42° from the antisolar direction. The commonly quoted value is about 42° for red light, with violet appearing at a somewhat smaller angle.

6 Marks Q21. Explain the complete formation of a primary rainbow with a labelled diagram.

Sunlight enters a water droplet and undergoes refraction and dispersion. The separated colours reach the opposite surface and undergo one internal reflection. They then leave the droplet after another refraction. Due to different deviations of different colours, red appears on the outer side and violet on the inner side of the primary rainbow.

6 Marks Q22. Explain the formation of a secondary rainbow.

In a secondary rainbow, sunlight enters the water droplet and is refracted and dispersed. The separated light undergoes two internal reflections before emerging after refraction. The additional reflection makes it fainter and reverses the colour order compared with the primary rainbow.

6 Marks Q23. Compare primary and secondary rainbows.

Primary: one internal reflection, brighter, red outer and violet inner, smaller angular radius.

Secondary: two internal reflections, fainter, violet outer and red inner, larger angular radius.

6 Marks Q24. Explain why a rainbow appears as an arc.

Only droplets at suitable angles send the separated light towards the observer's eye. These droplets form an approximate cone around the antisolar direction. The visible intersection of this geometry with the sky appears as an arc.

6 Marks Q25. Explain why a complete rainbow may sometimes be observed from an aircraft.

From an elevated position, the horizon may not block the lower portion of the rainbow. Under suitable Sun, observer and droplet geometry, the observer can see much more of the circular cone of rainbow light, sometimes nearly a complete circle.

6 Marks Q26. Why is the secondary rainbow outside the primary rainbow?

The additional internal reflection changes the direction in which the light emerges. Consequently, the secondary rainbow has a larger angular radius and appears outside the primary rainbow.

6 Marks Q27. Explain the importance of dispersion in rainbow formation.

Dispersion separates the wavelengths present in white sunlight. Because different colours are refracted differently by water, they emerge at different angles and become visible as separate colours.

6 Marks Q28. Why does the colour sequence reverse in a secondary rainbow?

The extra internal reflection changes the geometry of the rays inside the droplet before they emerge. This reverses the order in which the colours are seen compared with the primary rainbow.

6 Marks Q29. Explain the role of sunlight in rainbow formation.

Sunlight provides the white light that contains a continuous range of visible wavelengths. These wavelengths are refracted, dispersed and internally reflected by water droplets to form the rainbow.

6 Marks Q30. Explain the complete optical sequence involved in a rainbow.

The sequence is:

Refraction → Dispersion → Internal Reflection → Refraction

This sequence occurs in water droplets and produces the coloured light observed as a rainbow.

23. Assertion–Reason Questions

Q1.
Assertion: A primary rainbow involves one internal reflection inside a water droplet.
Reason: The dispersed light is reflected from the inner surface of the droplet.

Answer: Both Assertion and Reason are true, and the Reason correctly explains the Assertion.

Q2.
Assertion: The Sun is generally behind the observer when a primary rainbow is observed.
Reason: The light returning from the droplets travels towards the observer from the opposite part of the sky.

Answer: Both are true, and the Reason correctly explains the Assertion.

Q3.
Assertion: The secondary rainbow is usually fainter than the primary rainbow.
Reason: Light undergoes an additional internal reflection in the secondary rainbow.

Answer: Both are true, and the Reason correctly explains the Assertion.

Q4.
Assertion: Red is generally on the outer edge of the primary rainbow.
Reason: Red undergoes greater deviation than violet in water.

Answer: Assertion is true, but Reason is false.

Q5.
Assertion: Dispersion is important in rainbow formation.
Reason: Different wavelengths are refracted by different amounts.

Answer: Both are true, and the Reason correctly explains the Assertion.

24. HOTS Questions | उच्च स्तरीय चिंतन

HOTS 1: Why can two people standing at different positions not see exactly the same set of rainbow-producing droplets?

The required geometry depends on the observer's position. Different observers receive light from different droplets at the required angles. Therefore each observer effectively sees their own rainbow.

HOTS 2: Why does moving the observer change the position of the rainbow?

The rainbow is a geometrical optical phenomenon determined by the relative positions of the Sun, observer and water droplets. When the observer moves, the set of droplets satisfying the required geometry changes.

HOTS 3: Why is the rainbow not a physical object located at a fixed distance?

A rainbow is produced by light reaching the observer from suitable droplets at particular angles. It has no fixed physical surface or location like a solid object.

HOTS 4: Why is a secondary rainbow wider and fainter than the primary rainbow?

The secondary rainbow results from two internal reflections, changing the emergence geometry and giving a larger angular radius. The extra reflection also reduces the amount of light reaching the observer.

HOTS 5: Why does a rainbow usually disappear when the Sun becomes too high in the sky for an observer on the ground?

The required rainbow geometry may place the rainbow below the horizon when the Sun is sufficiently high. Hence the observer cannot see the necessary portion of the rainbow.

25. Diagram Labelling Practice

Label the following:

• Sunlight
• Water droplet
• Refraction
• Dispersion
• Internal reflection
• Emerging rays
• Red colour
• Violet colour

26. CBSE Golden Points | परीक्षा के लिए महत्वपूर्ण बिंदु

✔ Rainbow is a natural optical phenomenon.

✔ Water droplets act as tiny optical systems.

✔ Primary rainbow involves one internal reflection.

✔ Secondary rainbow involves two internal reflections.

✔ Refraction occurs when light enters and leaves a droplet.

✔ Dispersion separates white sunlight into colours.

✔ Primary rainbow: red outer, violet inner.

✔ Secondary rainbow: violet outer, red inner.

✔ Secondary rainbow is generally fainter.

✔ The Sun is generally behind the observer.

✔ Primary rainbow angular radius is roughly 40°–42°.

✔ Secondary rainbow is seen outside the primary rainbow.

✔ Alexander's dark band lies between primary and secondary rainbows.

✔ A complete circular rainbow may be visible from an elevated position under suitable conditions.

27. Memory Tricks | याद रखने की ट्रिक

🌈 Rainbow Formula:

Refraction → Dispersion → Internal Reflection → Refraction

☀️ Position Trick:

Sun Behind → Rainbow Ahead

🔴 Primary Rainbow:

Red → Outer
Violet → Inner

🔄 Secondary Rainbow:

Violet → Outer
Red → Inner

1 Reflection = Primary

2 Reflections = Secondary

28. One-Minute Revision | एक मिनट में पूरा टॉपिक

🌞 Sunlight enters water droplet.

↘ Refraction occurs.

🌈 White light disperses into colours.

↩ One internal reflection produces the primary rainbow.

↘ Light emerges after another refraction.

🔴 Red appears on outer side of primary rainbow.

🟣 Violet appears on inner side.

🌈 Primary rainbow is brighter.

🌈 Secondary rainbow involves two internal reflections.

🔄 Secondary rainbow has reversed colour order.

☀️ Sun is generally behind the observer.

29. Final Summary | अंतिम सारांश

A rainbow is produced when sunlight interacts with water droplets. The formation of a primary rainbow involves refraction, dispersion, one internal reflection and refraction again. The different wavelengths of sunlight are separated because they undergo different amounts of refraction in water.

प्राथमिक इन्द्रधनुष के निर्माण में सूर्य का प्रकाश जल की बूंद में प्रवेश करते समय अपवर्तित और विक्षेपित होता है। इसके बाद प्रकाश एक बार आंतरिक परावर्तन करता है और बाहर निकलते समय पुनः अपवर्तित होता है। परिणामस्वरूप विभिन्न रंग अलग-अलग दिशाओं में पर्यवेक्षक तक पहुँचते हैं।

🌞 Sunlight → 💧 Water Droplet → 🔺 Refraction → 🌈 Dispersion → ↩ Internal Reflection → 🌈 Rainbow