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O Level Physics Waves Sound Light Quiz

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Questions

O-Level Physics Quiz - Waves Sound Light

Name: __________________________
Class: __________________________
Date: __________________________
Score: ________ / 40

Duration: 45 minutes
Total Marks: 40

Instructions:

Answer all questions.
Write your answers in the spaces provided.
Show all working for calculation questions.
Use $g = 10 \text{ m/s}^2$ where necessary (though not typically required for this topic).
The speed of light in vacuum $c = 3.0 \times 10^8 \text{ m/s}$ .
The speed of sound in air $\approx 340 \text{ m/s}$ .

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

1. A transverse wave is travelling along a rope.
(a) Define what is meant by a transverse wave.
[1]

(b) State one example of a transverse wave other than waves on a rope.
[1]

2. Fig. 2.1 shows a displacement-distance graph for a wave at a specific instant in time.

(Imagine a sine wave starting at 0, peak at 2m, crossing axis at 4m, trough at 6m, crossing axis at 8m. Amplitude is 0.5m.)

(a) Determine the wavelength of the wave from the graph.
[1]
Wavelength = _______________ m

(b) Determine the amplitude of the wave.
[1]
Amplitude = _______________ m

3. A sound wave has a frequency of $250 \text{ Hz}$ and a wavelength of $1.36 \text{ m}$ in air.
(a) Calculate the speed of the sound wave.
[2]

Answer space

Speed = _______________ m/s

(b) The sound wave enters a block of steel. The speed of sound in steel is $5000 \text{ m/s}$ .
State what happens to the frequency and the wavelength of the sound as it enters the steel.
[2]
Frequency: _________________________________________________________
Wavelength: ________________________________________________________

4. Explain, in terms of particle motion, how a sound wave travels through air. In your answer, use the terms compression and rarefaction.
[3]

5. A ship sends a pulse of ultrasound vertically downwards into the sea. The pulse is reflected from the sea bed and detected $0.80 \text{ s}$ after it was sent. The speed of sound in sea water is $1500 \text{ m/s}$ .
Calculate the depth of the sea at this point.
[3]

Answer space

Depth = _______________ m

6. Two loudspeakers are connected to the same signal generator. A student walks along a line parallel to the speakers and hears alternating loud and quiet sounds.
(a) Name the wave phenomenon responsible for this effect.
[1]

(b) Explain why the student hears a quiet sound at certain positions.
[2]

7. Which of the following properties of a sound wave determines its pitch?
[1]
A. Amplitude
B. Frequency
C. Speed
D. Wavelength

Answer: _______

Section B: Light and Electromagnetic Spectrum (Questions 8–14)

8. Fig. 8.1 shows the electromagnetic spectrum with some regions missing.

Radio	Microwave	A	Visible	UV	B	Gamma

(a) Identify the regions labelled A and B.
[2]
A: __________________________
B: __________________________

(b) State two properties that are common to all electromagnetic waves in a vacuum.
[2]

9. A ray of light strikes a plane mirror at an angle of incidence of $40^\circ$ .
(a) Draw the reflected ray on Fig. 9.1 (not shown, assume standard diagram). Label the angle of reflection.
[1]
(Student to draw/label in mind or on scratch paper: Angle of reflection = $40^\circ$ )

(b) State the value of the angle of reflection.
[1]
Angle of reflection = _______________ $^\circ$

10. A ray of light travels from air into a glass block. The angle of incidence is $30^\circ$ and the angle of refraction is $19^\circ$ .
(a) Calculate the refractive index of the glass.
[2]

Answer space

Refractive index = _______________

(b) Calculate the critical angle for this glass.
[2]

Answer space

Critical angle = _______________ $^\circ$

11. Fig. 11.1 shows a ray of light entering a semi-circular glass block. The ray strikes the flat edge at the center.

(Diagram description: Ray enters curved side normally, travels to center of flat side. Angle of incidence at flat side is $45^\circ$ . Critical angle of glass is $42^\circ$ .)

(a) Explain why the ray does not refract as it enters the curved surface of the block.
[1]

(b) The angle of incidence at the flat boundary is $45^\circ$ . The critical angle for the glass is $42^\circ$ .
Describe what happens to the ray at the flat boundary and explain why.
[3]

12. Optical fibres are used in telecommunications and medicine.
(a) State the name of the phenomenon that allows light to travel through an optical fibre.
[1]

(b) Explain one advantage of using optical fibres instead of copper wires for transmitting information.
[1]

13. A converging lens has a focal length of $10 \text{ cm}$ . An object is placed $15 \text{ cm}$ from the lens.
(a) Describe the characteristics of the image formed (select three: real/virtual, upright/inverted, magnified/diminished).
[3]

(b) Give one practical use of a converging lens in this configuration (object between $F$ and $2F$ ).
[1]

14. Which region of the electromagnetic spectrum is used for thermal imaging cameras?
[1]
A. Ultraviolet
B. Infrared
C. Microwaves
D. X-rays

Answer: _______

Section C: Structured Problems & Applications (Questions 15–20)

15. A student investigates the refraction of light using a rectangular glass block.
(a) Describe how the student can measure the angle of refraction accurately. Include a sketch description if helpful.
[2]

(b) The student repeats the experiment with a block made of a different material with a higher refractive index. The angle of incidence is kept constant.
State and explain how the angle of refraction changes.
[2]

16. Fig. 16.1 shows a thin converging lens. $F$ is the principal focus. An object $O$ is placed on the principal axis.

(Diagram: Lens vertical line. F on left and right. Object O is to the left of the left F, i.e., $u < f$ .)

(a) Draw two rays from the top of the object to locate the image.
[3]
[Drawing space: 10 lines]

Answer space

(b) State the nature of the image formed.
[2]

17. An electromagnetic wave has a wavelength of $0.03 \text{ m}$ .
(a) Calculate its frequency.
[3]

Answer space

Frequency = _______________ Hz

(b) Identify the region of the electromagnetic spectrum to which this wave belongs.
[1]

18. Explain why astronauts in space cannot hear each other directly, even if they are close together, unless they use radio communication.
[2]

19. A periscope uses two plane mirrors to allow a viewer to see over an obstacle.
(a) Draw a ray diagram showing how light travels through a simple periscope with two mirrors angled at $45^\circ$ .
[3]
[Drawing space: 10 lines]

Answer space

(b) State one property of the final image compared to the original object in a standard periscope.
[1]

20. A white light source passes through a triangular glass prism.
(a) Name the phenomenon that causes the white light to split into a spectrum of colours.
[1]

(b) Explain why violet light is refracted more than red light.
[2]

End of Quiz

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Answers

O-Level Physics Quiz - Waves Sound Light (Answer Key)

Total Marks: 40

Section A: General Properties of Waves & Sound

1.
(a) A wave in which the particles of the medium vibrate perpendicular (at right angles) to the direction of wave energy propagation. [1]
(b) Light / Electromagnetic waves / Water waves (surface). [1]

2.
(a) Wavelength = distance between two consecutive peaks or equivalent points. From graph (0 to 8m is one full cycle? No, 0 to 4 is half. 0 to 8 is full). Wavelength = 8 m. [1]
(b) Amplitude = maximum displacement from equilibrium. Amplitude = 0.5 m. [1]

3.
(a) $v = f \lambda$
$v = 250 \times 1.36$
$v = 340 \text{ m/s}$ [2] (1 mark for formula/substitution, 1 for answer)
(b) Frequency: Stays the same (unchanged). [1]
Wavelength: Increases (because speed increases and $v=f\lambda$ ). [1]

The source vibrates, causing air particles to vibrate/oscillate. [1]
This creates regions of high pressure/density called compressions and regions of low pressure/density called rarefactions. [1]
These compressions and rarefactions propagate through the medium, transferring energy without transferring matter. [1]

Distance travelled by sound = speed $\times$ time
$d_{total} = 1500 \times 0.80 = 1200 \text{ m}$ [1]
This is the distance down and back (2 ways). [1]
Depth = $1200 / 2 = 600 \text{ m}$ . [1]

6.
(a) Interference (or Superposition). [1]
(b) Quiet sounds occur due to destructive interference. [1]
This happens when a compression from one speaker meets a rarefaction from the other (or waves are $180^\circ$ out of phase), cancelling each other out. [1]

7.
Answer: B (Frequency). [1]

Section B: Light and Electromagnetic Spectrum

8.
(a) A: Infrared [1]
B: X-rays [1]
(b) Any two of: [2]

Travel at the speed of light ( $3.0 \times 10^8 \text{ m/s}$ ) in vacuum.
Are transverse waves.
Can travel through a vacuum (do not require a medium).
Can be reflected, refracted, diffracted, and polarized.

9.
(a) Ray drawn reflecting off the mirror such that the angle with the normal is equal to the incident angle. [1]
(b) Angle of reflection = 40 $^\circ$ . [1]

10.
(a) $n = \frac{\sin i}{\sin r}$
$n = \frac{\sin 30^\circ}{\sin 19^\circ}$
$n = \frac{0.5}{0.3256} \approx 1.535$
Refractive index = 1.54 (or 1.5). [2]
(b) $\sin c = \frac{1}{n}$
$\sin c = \frac{1}{1.535}$
$c = \sin^{-1}(0.651)$
Critical angle = 40.6 $^\circ$ (accept 40-41). [2]

11.
(a) The ray enters along the normal (perpendicular to the surface), so the angle of incidence is $0^\circ$ . Therefore, there is no refraction (light does not bend). [1]
(b) The angle of incidence ( $45^\circ$ ) is greater than the critical angle ( $42^\circ$ ). [1]
Therefore, Total Internal Reflection occurs. [1]
The ray is reflected back into the glass block at an angle of reflection of $45^\circ$ . [1]

12.
(a) Total Internal Reflection. [1]
(b) Any one: [1]

Higher bandwidth / carries more data.
Less signal loss / attenuation over long distances.
Immune to electromagnetic interference.
Lighter and thinner than copper.

13.
(a) Object is at $15 \text{ cm}$ , $F=10 \text{ cm}$ . Object is between $F$ and $2F$ .
Image characteristics:

Real [1]
Inverted [1]
Magnified [1]
(b) Projector / Slide projector / Cinema projector. [1]

14.
Answer: B (Infrared). [1]

Section C: Structured Problems & Applications

15.
(a) Draw a normal line perpendicular to the surface at the point of entry. Measure the angle between the refracted ray and the normal using a protractor. [2]
(b) The angle of refraction becomes smaller. [1]
Explanation: A higher refractive index means light slows down more, causing it to bend more towards the normal. [1]

16.
(a) Ray Diagram: [3]

Ray parallel to principal axis refracts through the principal focus $F$ on the other side. [1]
Ray through the optical center passes undeviated. [1]
The rays diverge on the right side. They must be traced back (dashed lines) to the left to find where they appear to meet. [1]
(b) Nature of image: Virtual, Upright, Magnified. (Any two for 2 marks, or 1 mark for correct general description). [2]

17.
(a) $v = f \lambda \Rightarrow f = v / \lambda$
$f = \frac{3.0 \times 10^8}{0.03}$
$f = \frac{3.0 \times 10^8}{3.0 \times 10^{-2}}$
$f = 1.0 \times 10^{10} \text{ Hz}$ . [3] (1 mark formula, 1 mark substitution, 1 mark answer)
(b) Microwaves. [1]

18.
Sound is a mechanical wave that requires a medium (particles) to travel. [1]
Space is a vacuum (has no particles/air), so sound cannot propagate. [1]

19.
(a) Ray Diagram: [3]

Horizontal ray enters top, hits top mirror. [1]
Reflects downwards (angle $i=r=45^\circ$ ). [1]
Hits bottom mirror, reflects horizontally out to eye. [1]
(b) The image is upright (and laterally inverted, but upright is the key feature for seeing over obstacles). [1]

20.
(a) Dispersion. [1]
(b) Violet light has a higher frequency / shorter wavelength than red light. [1]
Therefore, violet light travels slower in glass and is refracted (bent) more than red light. [1]