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Secondary 3 Physics Waves Sound Light Quiz

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Questions

Secondary 3 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 clearly. Marks may be awarded for correct working even if the final answer is incorrect.
Take the acceleration due to gravity, $g = 10 \text{ m/s}^2$ (where applicable, though not primary for this topic).
Speed of sound in air $\approx 340 \text{ m/s}$ .
Speed of light in vacuum $c = 3.0 \times 10^8 \text{ m/s}$ .

Section A: Multiple Choice & Short Concepts (10 Marks)

1. Which of the following statements correctly describes the difference between transverse and longitudinal waves?
A. Transverse waves require a medium; longitudinal waves do not.
B. In transverse waves, particle vibration is parallel to wave direction; in longitudinal, it is perpendicular.
C. In transverse waves, particle vibration is perpendicular to wave direction; in longitudinal, it is parallel.
D. Transverse waves transfer matter; longitudinal waves transfer energy.

[1]

2. A sound wave travels from air into water. What happens to its frequency and speed?
A. Frequency increases, Speed increases
B. Frequency stays constant, Speed increases
C. Frequency stays constant, Speed decreases
D. Frequency decreases, Speed stays constant

[1]

3. Which region of the electromagnetic spectrum has the longest wavelength?
A. Gamma rays
B. Ultraviolet
C. Infrared
D. Radio waves

[1]

4. A ray of light strikes a plane mirror at an angle of incidence of $30^\circ$ . What is the angle between the incident ray and the reflected ray?
A. $30^\circ$
B. $60^\circ$
C. $90^\circ$
D. $120^\circ$

[1]

5. The diagram below shows a displacement-distance graph for a wave.

Displacement (cm)
      ^
  4   |       .--.
      |      /    \
  0   |-----/------\------> Distance (m)
      |    /        \
 -4   |   .          .
      |
      +------------------
      0    1    2    3    4

What is the wavelength of the wave?
A. 2 m
B. 4 m
C. 8 m
D. 16 m

[1]

6. State the SI unit for frequency.

[1]

7. Define the term amplitude of a wave.

[1]

8. Explain why sound cannot travel through a vacuum.

[1]

9. A student claps their hands and hears an echo from a wall 2 seconds later. If the speed of sound is $340 \text{ m/s}$ , calculate the distance from the student to the wall.

Distance = __________________________ m [2]

10. Which property of a sound wave determines its pitch?

[1]

Section B: Structured Questions (20 Marks)

11. A water wave travels across a ripple tank. The frequency of the vibrator is $5 \text{ Hz}$ and the wavelength is $4 \text{ cm}$ .

(a) Calculate the speed of the water wave in $\text{m/s}$ .

Speed = __________________________ $\text{m/s}$ [2]

(b) The frequency of the vibrator is doubled to $10 \text{ Hz}$ while the depth of the water remains constant.
(i) State what happens to the speed of the wave.

[1]

(ii) Calculate the new wavelength.

New Wavelength = __________________________ $\text{cm}$ [2]

12. The diagram below shows a ray of light entering a glass block from air.

      Air
      |
      |  Incident Ray
      \   /
       \ / i
--------|-------- Glass Surface
        |\
        | \ r
        |  \
        |   \
      Glass

(a) State the Law of Reflection.

[1]

(b) The angle of incidence $i$ is $40^\circ$ . The refractive index of the glass is $1.5$ .
Calculate the angle of refraction $r$ .

Angle $r$ = __________________________ $^\circ$ [3]

[2]

13. A converging lens has a focal length of $10 \text{ cm}$ . An object is placed $15 \text{ cm}$ from the lens.

(a) On the grid below, draw a ray diagram to show the formation of the image. Draw at least two rays from the top of the object. (Assume the object height is $2 \text{ cm}$ ).

      |
      |
      |
      |
------+---------------------- Principal Axis
      |
      |
      |
      |
      F           2F
      |           |
<-----|-----------|----->
      10cm        20cm
      (Lens at 0)

[3]

(b) State three characteristics of the image formed.

[3]

14. Ultrasound is used in medical imaging and industrial cleaning.

(a) Define ultrasound.

[1]

(b) Explain why ultrasound is preferred over audible sound for medical scanning of soft tissues.

[2]

Section C: Free Response & Application (10 Marks)

15. The electromagnetic spectrum consists of radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

(a) Arrange the following in order of increasing frequency:
Visible light, Radio waves, X-rays, Infrared.

[1]

(b) State one common use for Microwaves and one hazard associated with excessive exposure to Ultraviolet radiation.
Use: ___________________________________________________________________
Hazard: ________________________________________________________________
[2]

(c) All electromagnetic waves travel at the same speed in a vacuum. Calculate the frequency of a radio wave with a wavelength of $1500 \text{ m}$ .

Frequency = __________________________ $\text{Hz}$ [3]

16. Total Internal Reflection (TIR) is a phenomenon used in optical fibers.

(a) State the two conditions required for Total Internal Reflection to occur.

[2]

(b) The critical angle for a certain type of glass is $42^\circ$ .
If a ray of light travels inside this glass and hits the boundary with air at an angle of incidence of $45^\circ$ , describe what happens to the ray.

[2]

17. A guitar string vibrates to produce a sound note.

(a) Describe how the vibration of the string produces a sound wave in the surrounding air.

[2]

(b) If the tension in the string is increased, the frequency of the note produced increases. State what happens to the pitch of the sound heard.

[1]

18. White light passes through a glass prism and splits into a spectrum of colors.

(a) Name this phenomenon.

[1]

(b) Which color of light is refracted the most by the prism?

[1]

[2]

19. A diver underwater looks up at a bird flying in the air above the water surface.

(a) Does the bird appear higher or lower than its actual position?

[1]

(b) Explain your answer in (a) by referring to the bending of light rays.

[3]

20. Seismic waves generated by earthquakes include P-waves (longitudinal) and S-waves (transverse).

(a) Which type of seismic wave can travel through the Earth's liquid outer core? Explain your answer.

[2]

(b) S-waves travel at $4.5 \text{ km/s}$ . Calculate the time taken for an S-wave to travel $900 \text{ km}$ .

Time = __________________________ s [2]

Answers

Secondary 3 Physics Quiz - Waves Sound Light (Answer Key)

1. C
Reasoning: Transverse waves vibrate perpendicular to energy transfer (e.g., light, water ripples). Longitudinal waves vibrate parallel to energy transfer (e.g., sound).

2. B
Reasoning: Frequency is determined by the source and does not change when the wave changes medium. Speed generally increases when sound moves from a gas (air) to a liquid (water) because particles are closer together.

3. D
Reasoning: Radio waves have the longest wavelength and lowest frequency in the EM spectrum. Gamma rays have the shortest wavelength.

4. B
Reasoning: Angle of incidence = $30^\circ$ . By law of reflection, angle of reflection = $30^\circ$ . The angle between the rays is $30^\circ + 30^\circ = 60^\circ$ .

5. B
Reasoning: Wavelength is the distance between two consecutive points in phase (e.g., crest to crest). The graph shows one full cycle from $0$ to $4 \text{ m}$ .

6. Hertz (Hz)

7. Amplitude is the maximum displacement of a particle from its rest (equilibrium) position.

8. Sound is a mechanical wave that requires a medium (particles) to propagate energy via vibrations/compressions. A vacuum has no particles, so sound cannot travel.

9. 340 m
Working:
Total distance traveled by sound = Speed $\times$ Time
$d_{total} = 340 \text{ m/s} \times 2 \text{ s} = 680 \text{ m}$
This is the distance to the wall and back.
Distance to wall = $680 / 2 = 340 \text{ m}$ .

10. Frequency

11.
(a) 0.2 m/s
Working:
$v = f \lambda$
$f = 5 \text{ Hz}$ , $\lambda = 4 \text{ cm} = 0.04 \text{ m}$
$v = 5 \times 0.04 = 0.2 \text{ m/s}$

(b) (i) Stays constant
Reasoning: The speed of a water wave depends on the depth of the water. Since depth is constant, speed is constant.

(ii) 2 cm
Working:
$v = 0.2 \text{ m/s}$ (constant)
$f_{new} = 10 \text{ Hz}$
$\lambda_{new} = v / f_{new} = 0.2 / 10 = 0.02 \text{ m} = 2 \text{ cm}$

12.
(a) The angle of incidence is equal to the angle of reflection. (Both measured from the normal).

(b) 25.4 $^\circ$ (Accept 25 $^\circ$ - 25.5 $^\circ$ )
Working:
Snell's Law: $n = \frac{\sin i}{\sin r}$
$1.5 = \frac{\sin 40^\circ}{\sin r}$
$\sin r = \frac{\sin 40^\circ}{1.5}$
$\sin r = \frac{0.6428}{1.5} \approx 0.4285$
$r = \sin^{-1}(0.4285) \approx 25.37^\circ$

(c) Light slows down when entering a denser medium (glass) from a less dense medium (air). This change in speed causes the wavefronts to bend, resulting in the ray bending towards the normal.

13.
(a) Ray Diagram:

Ray parallel to principal axis refracts through the focal point (F) on the other side.
Ray through the optical center passes undeviated.
The rays intersect on the other side of the lens, beyond 2F.
Image should be drawn inverted and larger than the object.

(b) Characteristics:

Real
Inverted
Magnified (Larger than object)

14.
(a) Ultrasound refers to sound waves with frequencies above the upper limit of human hearing (greater than $20,000 \text{ Hz}$ or $20 \text{ kHz}$ ).

(b) Ultrasound has a higher frequency and shorter wavelength, allowing it to resolve smaller details (better resolution) and penetrate soft tissues effectively without the damaging ionizing effects of X-rays.

15.
(a) Radio waves, Infrared, Visible light, X-rays.

(b)
Use: Cooking / Heating food / Satellite communication / Radar.
Hazard: Skin cancer / Sunburn / Damage to eyes (cataracts) / Premature skin aging.

(c) 200,000 Hz (or $2 \times 10^5 \text{ Hz}$ )
Working:
$c = f \lambda$
$3.0 \times 10^8 \text{ m/s} = f \times 1500 \text{ m}$
$f = \frac{3.0 \times 10^8}{1500}$
$f = \frac{300,000,000}{1500} = 200,000 \text{ Hz}$

16.
(a)

Light must travel from a optically denser medium to a less dense medium (e.g., glass to air).
The angle of incidence must be greater than the critical angle.

(b) The angle of incidence ( $45^\circ$ ) is greater than the critical angle ( $42^\circ$ ). Therefore, Total Internal Reflection occurs. The light ray is completely reflected back into the glass; no light escapes into the air.

17.
(a) The vibrating string pushes and pulls the surrounding air molecules, creating regions of compression and rarefaction. These disturbances propagate outwards as a longitudinal sound wave.

(b) The pitch becomes higher.

18.
(a) Dispersion.

(b) Violet.

(c) Different colors (wavelengths) of light travel at slightly different speeds in glass. Violet light travels slower than red light in glass, causing it to refract (bend) more.

19.
(a) Higher.

(b) Light rays from the bird travel from air (less dense) to water (denser). They bend towards the normal upon entering the water. The diver's eye traces these rays back in a straight line, forming a virtual image that appears higher than the actual position of the bird.

20.
(a) P-waves. P-waves are longitudinal waves, which can travel through solids, liquids, and gases. S-waves are transverse and cannot travel through liquids.

(b) 200 s
Working:
$t = \frac{d}{v}$
$t = \frac{900 \text{ km}}{4.5 \text{ km/s}}$
$t = 200 \text{ s}$