Pembahasan Tryout TOEFL ITP Reading Comprehension Part 3

Passage 1: The Process of Rainbow Formation

A rainbow is one of the most fascinating atmospheric optical phenomena. It occurs as a result of the complex interaction between sunlight and water droplets in the atmosphere. After rainfall, the air is often filled with tiny suspended water droplets, creating ideal conditions for a rainbow to form. Under certain circumstances, sunlight striking these water droplets undergoes several optical processes, namely refraction, internal reflection, and subsequent refraction as it exits the droplet.

The process of rainbow formation begins when sunlight enters the water droplet and undergoes its first refraction. This occurs because of the change in medium from air to water, which has a higher refractive index. As a result of this refraction, white light, which is composed of various wavelengths, starts to separate into its component colors. This phenomenon is known as light dispersion, where each color of light is refracted at a different angle according to its wavelength.

After the initial refraction, the light that has been dispersed is internally reflected off the inner surface of the droplet. This reflection causes the light to remain inside the droplet temporarily. Subsequently, the light undergoes a second refraction as it exits the droplet and enters the air. During this process, the separation of colors becomes more distinct, with each color exiting at different angles.

As a result of this refraction and reflection, a spectrum of colors is visible to the observer. Red, which has the longest wavelength, appears on the outer edge of the rainbow, while violet, with the shortest wavelength, appears on the inner edge. The common sequence of colors observed in a rainbow is red, orange, yellow, green, blue, indigo, and violet. Each color appears due to light exiting the droplet at a specific angle, typically around 42 degrees from the direction of the incoming sunlight.

A rainbow usually appears as a semi-circle because of this angular arrangement. When the observer is at a higher vantage point, such as in an airplane, a full circular rainbow may be visible. In addition to primary rainbows, there are secondary rainbows that sometimes appear outside the primary rainbow. A secondary rainbow is formed due to two internal reflections within the water droplet, resulting in a fainter spectrum with the color sequence reversed.

The phenomenon of the rainbow not only represents natural beauty but also illustrates fundamental principles of optical physics. Through an understanding of refraction, reflection, and light dispersion, we can appreciate how the simple combination of sunlight and water droplets can create such a visually stunning display. A rainbow serves as a tangible reminder of how natural laws can generate extraordinary beauty in the world around us.

1. What is the main idea of the passage?
Jawaban: B. The interaction of sunlight and water droplets

Pembahasan:
Pertanyaan "main idea" menanyakan gagasan utama dari seluruh bacaan.
Dalam passage tersebut, seluruh paragraf membahas bagaimana sinar matahari berinteraksi dengan tetesan air melalui proses pembiasan, pemantulan, dan dispersi untuk menghasilkan pelangi.
Pilihan lain (A, C, D) hanya bagian kecil dari pembahasan, bukan keseluruhan isi.

2. According to the passage, what causes the dispersion of light in a water droplet?
Jawaban: B. The refraction of light due to the change in medium

Pembahasan:
Dispersi cahaya terjadi ketika cahaya berpindah dari udara ke air, yang memiliki indeks bias berbeda, sehingga arah cahaya berubah dan terurai menjadi warna-warna berbeda.
Jawaban A, C, dan D kurang tepat karena yang disebut dalam passage adalah pembiasan (refraction), bukan perubahan kecepatan murni, pantulan saja, atau penyerapan.

3. What happens to light after it enters a water droplet?
Jawaban: B. It is refracted, then reflected inside the droplet before exiting.

Pembahasan:
Setelah memasuki tetesan air, cahaya dibiasakan (refracted), dipantulkan di dalam tetesan (internally reflected), lalu dibiasakan lagi saat keluar.
Pilihan lain salah karena:

• A: hanya pantulan tanpa pembiasan tidak sesuai,

• C: tidak mengalami pembiasan salah,

• D: cahaya tidak diserap melainkan tetap dipantulkan dan dibiasakan.

4. What is the main reason why red light appears on the outer edge of the rainbow?
Jawaban: C. It has a longer wavelength than other colors.

Pembahasan:
Dalam pembentukan pelangi, merah memiliki panjang gelombang terpanjang, sehingga dibelokkan (dibiasakan) dengan sudut yang lebih kecil dibandingkan warna lain.
Karena itu, merah tampak di bagian luar pelangi.
Pilihan A dan B salah karena merah justru panjang gelombangnya panjang (bukan pendek) dan sudut biasnya lebih kecil.

5. What is the angle at which light typically exits the droplet in the formation of a rainbow?
Jawaban: C. 42 degrees

Pembahasan:
Passage menyebutkan bahwa sinar keluar dari tetesan dengan sudut sekitar 42 derajat terhadap arah datangnya cahaya matahari.
Pilihan A, B, dan D (90°, 45°, 30°) tidak sesuai dengan yang disebut dalam teks.

6. In the passage, the word "dispersion" most closely means:

Jawaban: B. The spreading out of light

Pembahasan:

• Kata "dispersion" dalam konteks optik berarti pemecahan atau penyebaran cahaya putih menjadi warna-warna berbeda karena perbedaan panjang gelombang.

• Dalam passage, dispersion terjadi saat cahaya putih memasuki tetesan air, lalu terurai menjadi warna merah, oranye, kuning, dst.

• Pilihan lain salah karena:

  • A (reflection) → pemantulan, bukan pemecahan warna.

  • C (absorption) → penyerapan cahaya, tidak dibahas di sini.

  • D (change in direction) → itu pembiasan (refraction), bukan dispersion.

7. How does a secondary rainbow differ from a primary rainbow, according to the passage?

Jawaban: C. It has a reversed color sequence and is fainter.

Pembahasan:

• Passage menjelaskan bahwa secondary rainbow terbentuk karena dua kali pemantulan internal di dalam tetesan air.

• Akibatnya, urutan warna terbalik (merah di bagian dalam, ungu di luar) dan warnanya lebih redup dibanding primary rainbow.

• Pilihan lain salah karena:

  • A (It is brighter) → justru secondary rainbow lebih redup.

  • B (It is formed with only one reflection) → secondary rainbow terjadi karena dua refleksi.

  • D (It appears below the primary rainbow) → secondary rainbow muncul di atas primary rainbow.

8. What does the passage suggest about the visibility of a full circular rainbow?

Jawaban: B. It can be seen when the observer is at a high vantage point.

Pembahasan:

• Biasanya dari permukaan tanah kita hanya melihat setengah lingkaran pelangi.

• Namun, jika pengamat berada di tempat tinggi (seperti di atas bukit atau dalam pesawat), pelangi bisa terlihat sebagai lingkaran penuh.

• Pilihan lain salah karena:

  • A (Only during sunrise) → tidak ada batasan waktu spesifik di passage.

  • C (Only after multiple rain showers) → tidak disebut.

  • D (When the sun is directly overhead) → pelangi terbentuk ketika matahari rendah, bukan overhead.

9. Which of the following is NOT a process described in the formation of a rainbow?

Jawaban: C. Absorption

Pembahasan:

• Dalam pembentukan pelangi, tiga proses utama yang disebut dalam passage adalah:

  • Refraction (pembiasan)

  • Reflection (pemantulan)

  • Dispersion (pemecahan cahaya)

• Absorption (penyerapan) tidak disebut sebagai bagian dari proses terbentuknya pelangi.

• Karena itu, C adalah jawaban yang benar.

10. What is the significance of understanding the processes of refraction, reflection, and dispersion in relation to rainbows?

Jawaban: A. It helps explain the scientific principles behind rainbows.

Pembahasan:

• Dengan memahami bagaimana pembiasan, pemantulan, dan dispersion bekerja, kita jadi tahu secara ilmiah bagaimana pelangi bisa terbentuk.

• Pilihan lain salah karena:

  • B (It predicts the exact location) → proses ini menjelaskan formasi, bukan prediksi lokasi spesifik.

  • C (It determines weather patterns) → pelangi tidak menentukan pola cuaca.

  • D (It measures the size of raindrops) → ukuran tetesan air memang memengaruhi warna, tapi itu bukan fokus utama pembahasan.

11. In the sentence "As a result of this refraction and reflection, a spectrum of colors is visible to the observer," what does the word "this" refer to?

Jawaban: C. The process of refraction and reflection

Pembahasan:

• Kata "this" di kalimat itu menunjuk pada sesuatu yang sudah disebut sebelumnya.

• Di passage, sebelum kalimat ini, dijelaskan tentang proses pembiasan (refraction) dan pemantulan (reflection) cahaya di dalam tetesan air.

• Jadi, "this" merujuk pada gabungan proses pembiasan dan pemantulan yang menyebabkan cahaya terurai menjadi spektrum warna.

• Pilihan lain salah karena:

  • A (light entering the droplet) → hanya awal proses, belum lengkap.

  • B (angle of exit) → hanya sebagian kecil dari proses.

  • D (color spectrum) → itu akibatnya, bukan penyebabnya.

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