O Level Physics Waves Sound Light Quiz

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O-Level Physics Quiz - Waves Sound Light

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 55

Duration: 60 Minutes
Total Marks: 55

Instructions:

• Answer all questions.
• For calculation questions, show all working and state the final answer with the correct unit.
• Use $g = 10\text{ m/s}^2$ and the speed of light $c = 3.0 \times 10^8\text{ m/s}$ where necessary.
• Use 2 or 3 significant figures for numerical answers.

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Section A: General Properties of Waves & Sound (Questions 1–7)

1. Define the term frequency of a wave. [1]
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2. A wave has a frequency of 50 Hz and a wavelength of 0.4 m. Calculate the speed of the wave. [2]
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3. State two differences between a transverse wave and a longitudinal wave. [2]
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4. Explain why sound waves cannot travel through a vacuum. [2]
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5. A student observes a sound wave with a high amplitude and a low frequency. Describe the characteristics of the sound in terms of loudness and pitch. [2]
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6. An echo is heard 1.2 seconds after a sound is produced. If the speed of sound in air is $340\text{ m/s}$, calculate the distance of the reflecting surface from the source. [3]
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7. State one application of ultrasound in medicine and explain how it is used. [2]
   
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Section B: Electromagnetic Spectrum (Questions 8–13)

8. List the electromagnetic spectrum in order of increasing frequency. [1]
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9. Which EM wave is used in thermal imaging cameras? [1]
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10. Explain why X-rays are used for security screening at airports instead of visible light. [2]
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11. State one hazard associated with high-frequency EM waves, such as Gamma rays. [1]
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12. A microwave has a wavelength of $1.2\text{ cm}$. Calculate its frequency. [3]
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13. Compare the speed of radio waves and X-rays in a vacuum. [1]
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Section C: Light & Optics (Questions 14–20)

14. State the law of reflection. [1]
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15. A ray of light enters a glass block from air. Explain why the ray bends towards the normal. [2]
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16. The refractive index of a diamond is 2.42. Calculate the speed of light in diamond. [2]
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17. Define the critical angle of a medium. [2]
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18. A ray of light is incident at an angle of $50^\circ$ to the normal in a medium with a critical angle of $42^\circ$. State and explain what happens to the ray. [2]
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19. Describe the use of optical fibres in telecommunications. [2]
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20. A converging lens has a focal length of $10\text{ cm}$. An object is placed $15\text{ cm}$ from the lens. (a) Sketch a ray diagram to locate the image. [3] (b) State two characteristics of the image formed. [2]
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Answer Key - O-Level Physics Quiz (Waves Sound Light)

1. Frequency: The number of complete waves passing a point per second. (1)
2. $v = f\lambda = 50 \times 0.4 = 20\text{ m/s}$. (2)
3. Differences:
   • Transverse: Oscillations are perpendicular to direction of energy transfer; Longitudinal: Oscillations are parallel to direction of energy transfer. (2)
   • Examples: Light (Transverse) vs Sound (Longitudinal).
4. Sound waves are mechanical waves that require a medium (particles) to propagate via compressions and rarefactions; a vacuum has no particles to transmit the vibration. (2)
5. Loudness: Loud (due to high amplitude). Pitch: Low (due to low frequency). (2)
6. $d = \frac{v \times t}{2} = \frac{340 \times 1.2}{2} = 204\text{ m}$. (3)
7. Application: Fetal scanning/Ultrasound imaging. Explanation: Ultrasound pulses are sent into the body and the time taken for echoes to return is used to map the internal structure. (2)
8. Radio $\rightarrow$ Microwave $\rightarrow$ Infrared $\rightarrow$ Visible $\rightarrow$ UV $\rightarrow$ X-ray $\rightarrow$ Gamma. (1)
9. Infrared. (1)
10. X-rays have higher energy/frequency and can penetrate materials (like clothing/plastic) that visible light cannot, allowing the internal structure of luggage to be seen. (2)
11. Ionizing radiation can damage cells/DNA, leading to mutations or cancer. (1)
12. $f = \frac{c}{\lambda} = \frac{3.0 \times 10^8}{0.012} = 2.5 \times 10^{10}\text{ Hz}$. (3)
13. They travel at the same speed ($3.0 \times 10^8\text{ m/s}$). (1)
14. The angle of incidence is equal to the angle of reflection. (1)
15. Light travels slower in glass than in air; the change in speed causes the ray to bend towards the normal. (2)
16. $v = \frac{c}{n} = \frac{3.0 \times 10^8}{2.42} \approx 1.24 \times 10^8\text{ m/s}$. (2)
17. The angle of incidence in the denser medium for which the angle of refraction is $90^\circ$. (2)
18. Total Internal Reflection (TIR) occurs. Because the angle of incidence ($50^\circ$) is greater than the critical angle ($42^\circ$), the ray is reflected back into the medium. (2)
19. Light signals are transmitted as pulses of light that undergo repeated TIR inside the core, allowing data to travel long distances with minimal loss. (2)
20. (a) Diagram should show: Ray parallel to axis $\rightarrow$ through focal point; Ray through optical center $\rightarrow$ straight. Intersection should be beyond $10\text{ cm}$ from lens on the other side. (3) (b) Real, Inverted, Magnified. (Any two) (2)