🌊 Chapter 12: Waves – Constructed Response Questions
Prepared by Muhammad Tayyab, Subject Specialist Physics, Govt Christian High School Daska. Based on PECTAA 2026 syllabus (National Curriculum 2023).
📖 What's Inside: This section covers constructed response questions from the official PECTAA 2026 curriculum: Why sound cannot travel through space but light can, particle motion in transverse waves, amplitude-energy relationship, diffraction of sound around walls, and wave behavior when slit size is smaller than wavelength. Each answer is presented in the exact exam-ready format.
📚 Related Resources – Chapter 12: Waves
Constructed response questions help build deeper conceptual understanding for board exams.
✏️ Constructed Response Questions & Answers (PECTAA 2026)
12.1 Why sound cannot travel through space, but light can? Explain using the concept of wave types.
Sound cannot travel through space because sound waves are mechanical waves that require a material medium (solid, liquid, or gas) to propagate. Space is a vacuum with no particles to transmit vibrations. Light can travel through space because light waves are electromagnetic waves that do not require a medium; they can travel through empty space by self-propagating electric and magnetic fields.
Sound cannot travel through space because sound waves are mechanical waves that require a material medium (solid, liquid, or gas) to propagate. Space is a vacuum with no particles to transmit vibrations. Light can travel through space because light waves are electromagnetic waves that do not require a medium; they can travel through empty space by self-propagating electric and magnetic fields.
12.2 A student shakes one end of a rope and observes waves move along it. What kind of wave is this, and how do the particles move?
This is a transverse wave. In a transverse wave, the particles of the rope vibrate at right angles (perpendicular) to the direction in which the wave is travelling. When the student shakes the rope up and down, the wave moves horizontally along the rope, while each particle moves vertically up and down.
This is a transverse wave. In a transverse wave, the particles of the rope vibrate at right angles (perpendicular) to the direction in which the wave is travelling. When the student shakes the rope up and down, the wave moves horizontally along the rope, while each particle moves vertically up and down.
12.3 How does the amplitude of a wave relate to the energy it carries? Give an example to support your answer.
The amplitude of a wave represents the amount of energy it carries. A wave with greater amplitude carries more energy, while a wave with smaller amplitude carries less energy. The energy is proportional to the square of the amplitude. For example, a loud sound has a larger amplitude than a soft sound, so it carries more energy and sounds louder. Similarly, a brighter light has larger amplitude than dim light.
The amplitude of a wave represents the amount of energy it carries. A wave with greater amplitude carries more energy, while a wave with smaller amplitude carries less energy. The energy is proportional to the square of the amplitude. For example, a loud sound has a larger amplitude than a soft sound, so it carries more energy and sounds louder. Similarly, a brighter light has larger amplitude than dim light.
12.4 Why do we still hear a person talking even if he is behind a wall? Explain using the concept of diffraction.
We can hear a person behind a wall due to diffraction of sound waves. Diffraction is the bending and spreading of waves around obstacles or through openings. Sound waves have relatively long wavelengths (compared to light), so they can easily bend around the edges of the wall and spread into the region behind it. Even without a direct line of sight, diffracted sound waves reach our ears. Light waves have very short wavelengths and diffract very little, so we cannot see around the wall.
We can hear a person behind a wall due to diffraction of sound waves. Diffraction is the bending and spreading of waves around obstacles or through openings. Sound waves have relatively long wavelengths (compared to light), so they can easily bend around the edges of the wall and spread into the region behind it. Even without a direct line of sight, diffracted sound waves reach our ears. Light waves have very short wavelengths and diffract very little, so we cannot see around the wall.
12.5 If size of slit a wave passes through is much smaller than the wavelength, what will happen to the wave after passing through the slit? Explain briefly.
When the size of the slit is smaller than the wavelength (or comparable to the wavelength), the waves exhibit maximum diffraction. The wave spreads out significantly after passing through the slit, forming strong circular or semicircular wavefronts on the other side. The smaller the slit compared to the wavelength, the greater the spreading effect. This is a fundamental property of wave behavior, showing that waves can bend around corners and spread widely when encountering obstacles smaller than their wavelength.
When the size of the slit is smaller than the wavelength (or comparable to the wavelength), the waves exhibit maximum diffraction. The wave spreads out significantly after passing through the slit, forming strong circular or semicircular wavefronts on the other side. The smaller the slit compared to the wavelength, the greater the spreading effect. This is a fundamental property of wave behavior, showing that waves can bend around corners and spread widely when encountering obstacles smaller than their wavelength.
📐 Key Concepts – Waves (Constructed Response Context)
Wave Speed Relation: \( v = f \lambda \)
Energy ∝ (Amplitude)²: \( E \propto A^2 \)
Diffraction Condition: Significant when \( a \approx \lambda \) or \( a < \lambda \)
💡 Exam Tip:
For board exams, always distinguish between mechanical and electromagnetic waves clearly. In constructed response questions, explain the physical reasoning behind each phenomenon — such as why sound requires a medium or how amplitude ties to energy. Use key terms like transverse vs longitudinal, diffraction, and wave-particle interaction. These answers follow the official PECTAA 2026 pattern and are prepared by Subject Specialist Muhammad Tayyab.
Unit 10✨ Thermal Physics
Unit 11Transfer of Thermal Energy
Unit 12Waves
Unit 13Sound
Unit 14Light
Unit 15Electrostatics
Unit 16Electricity
Unit 17Electromagnetism
Unit 18Electromagnetic Induction & EM Waves
Unit 19Electronics
Unit 20Atomic and Nuclear Physics
Unit 21Space and Environment
📖 Complete syllabus coverage for Class 10 Physics (PECTAA 2026) – Units 10 to 21
Created by Hira Science Academy | Aligned with PECTAA 2026 Syllabus