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Secondary 4 Pure Physics Waves Sound Light Quiz

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Questions

Secondary 4 Pure Physics Quiz - Waves Sound Light

Name: _________________________ Class: _________________________ Date: _________________________ Score: ______ / 40

Duration: 45 minutes Total Marks: 40

Instructions:

Answer ALL questions in the spaces provided.
Show all working for calculation questions.
Take g = 10 m/s² unless otherwise stated.
The number of marks is given in brackets [ ] at the end of each question or part question.

Section A: General Wave Properties (Questions 1–5)

[10 marks]

1. A wave travels along a stretched slinky spring. The coils of the spring vibrate parallel to the direction of wave travel.

(a) State the type of wave travelling along the spring. [1]

(b) The wave has a frequency of 5.0 Hz and a wavelength of 0.40 m. Calculate the speed of the wave. [2]

2. Figure 1 shows the displacement-distance graph of a water wave at a particular instant.

Displacement / cm
    ^
  2 |    *         *         *
    |   / \       / \       / \
  0 |--*---*-----*---*-----*---*---> Distance / m
    |       \   /       \   /
 -2 |        *-*         *-*
    |
    |<---- 0.8 m ---->

(a) Determine the amplitude of the wave. [1]

(b) Determine the wavelength of the wave. [1]

(d) On the axes below, sketch the displacement-time graph for a point on the water surface at x = 0 m, for a time interval of 0.8 s. [1]

Displacement / cm
    ^
  2 |
    |
  0 |--------------------------------------------------> Time / s
    |
 -2 |

3. A student makes the following statement:

"Waves transfer matter from one place to another."

Explain why this statement is incorrect. [1]

4. A sound wave travels through air at 340 m/s. The frequency of the sound is 680 Hz.

(a) Calculate the wavelength of the sound wave. [2]

(b) State the relationship between the period and frequency of a wave. [1]

5. A transverse wave and a longitudinal wave both travel at the same speed in the same medium. The transverse wave has a frequency of 10 Hz and a wavelength of 0.50 m.

(a) Calculate the speed of the transverse wave. [1]

(b) The longitudinal wave has a wavelength of 1.0 m. Calculate its frequency. [1]

Section B: Sound (Questions 6–10)

[10 marks]

6. A loudspeaker produces sound waves in air.

(a) Describe how the loudspeaker cone produces compressions and rarefactions in the air. [2]

(b) State two differences between sound waves and light waves. [2]

7. A ship uses sonar to detect a shoal of fish. A pulse of sound is emitted from the ship and the echo is received 0.80 s later. The speed of sound in water is 1500 m/s.

(a) Calculate the distance between the ship and the shoal of fish. [2]

(b) Explain why ultrasound is used for sonar rather than audible sound. [1]

8. A musician plays a note on a guitar. The string vibrates with a frequency of 440 Hz.

(a) State what determines the pitch of the note heard. [1]

(b) The musician plucks the string harder. State what happens to the amplitude of vibration and the loudness of the sound. [2]

Amplitude: _________________________________________________________________________

Loudness: _________________________________________________________________________

9. An echo is heard 1.2 s after a person shouts towards a cliff face. The speed of sound in air is 340 m/s.

Calculate the distance of the person from the cliff face. [2]

10. A student investigates the speed of sound by standing 170 m from a large wall and clapping two wooden blocks together. She adjusts her clapping rate until each clap coincides with the echo of the previous clap. She makes 40 claps in 20 seconds.

(a) Calculate the time interval between successive claps. [1]

(b) Calculate the speed of sound from this experiment. [2]

Section C: Light (Questions 11–15)

[10 marks]

11. A ray of light travels from air into glass. The angle of incidence is 45° and the angle of refraction is 28°.

(a) Calculate the refractive index of the glass. [2]

(b) State what happens to the speed of light when it enters the glass. [1]

12. Figure 2 shows a ray of light travelling from water (refractive index = 1.33) towards air.

    Air (n = 1.00)
    --------------------
    Water (n = 1.33)
         \
          \
           \  θ
            \
             \

(a) Calculate the critical angle for the water-air boundary. [2]

(b) The angle of incidence θ is 55°. State and explain what happens to the light at the boundary. [2]

13. A converging lens has a focal length of 10 cm. An object is placed 25 cm from the lens.

(a) State whether the image formed is real or virtual. [1]

(b) State whether the image is magnified or diminished. [1]

14. Optical fibres are used in telecommunications to transmit signals over long distances.

(a) Name the phenomenon that allows light to travel along an optical fibre without escaping. [1]

(b) State two conditions necessary for this phenomenon to occur. [2]

15. A ray of light strikes a plane mirror at an angle of incidence of 30°.

(a) State the angle of reflection. [1]

(b) State two characteristics of the image formed by a plane mirror. [2]

Section D: Electromagnetic Spectrum and Integrated Questions (Questions 16–20)

[10 marks]

16. The electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

(a) State the property that is the same for all electromagnetic waves in a vacuum. [1]

(b) State the region of the electromagnetic spectrum that has the highest frequency. [1]

17. A microwave oven uses electromagnetic waves of frequency 2.45 × 10⁹ Hz. The speed of electromagnetic waves in air is 3.0 × 10⁸ m/s.

(a) Calculate the wavelength of the microwaves. [2]

(b) Explain why microwave ovens have metal screens on the door. [1]

18. A student listens to a radio broadcast. The radio waves travel from the transmitter to the radio at 3.0 × 10⁸ m/s. The wavelength of the radio waves is 300 m.

(a) Calculate the frequency of the radio waves. [2]

(b) State one difference between radio waves and sound waves. [1]

19. Ultraviolet radiation from the Sun can be harmful to humans.

(a) State one harmful effect of overexposure to ultraviolet radiation. [1]

(b) State one beneficial use of ultraviolet radiation. [1]

20. A ray of light enters a glass block of refractive index 1.52 from air. The angle of incidence is 60°.

(a) Calculate the angle of refraction in the glass. [2]

(b) The ray then travels from the glass back into air. State the condition under which the ray would undergo total internal reflection at the glass-air boundary. [1]

END OF QUIZ

Check your answers carefully before submitting.

Answers

Secondary 4 Pure Physics Quiz - Waves Sound Light — Answer Key

Total Marks: 40

Section A: General Wave Properties (Questions 1–5)

1. (a) Longitudinal wave [1]

(b) v = fλ = 5.0 × 0.40 = 2.0 m/s [2]

Award [1] for correct formula, [1] for correct answer with unit.

(c) In a longitudinal wave, particles vibrate parallel to the direction of wave travel; in a transverse wave, particles vibrate perpendicular to the direction of wave travel. [1]

Accept any valid difference.

2. (a) Amplitude = 2 cm [1]

(b) Wavelength = 0.8 m [1]

Award [1] for correct formula, [1] for correct answer with unit.

(d) Sinusoidal graph with period T = 1/f = 0.4 s, amplitude 2 cm, showing two complete cycles from t = 0 to t = 0.8 s. [1]

Award [1] for correct shape, period, and amplitude.

3. Waves transfer energy without transferring matter. The particles of the medium oscillate about their equilibrium positions but do not travel with the wave. [1]

Accept any clear explanation that waves transfer energy, not matter.

4. (a) λ = v/f = 340/680 = 0.50 m [2]

Award [1] for correct formula, [1] for correct answer with unit.

(b) Period = 1/frequency (or T = 1/f) [1]

5. (a) v = fλ = 10 × 0.50 = 5.0 m/s [1]

(b) f = v/λ = 5.0/1.0 = 5.0 Hz [1]

Award [1] for correct answer with unit.

Section B: Sound (Questions 6–10)

6. (a) When the loudspeaker cone moves forward, it pushes air particles together, creating a compression (region of high pressure). When the cone moves backward, it creates a region where air particles are spread apart, forming a rarefaction (region of low pressure). [2]

Award [1] for compression explanation, [1] for rarefaction explanation.

(b) Any two from: [2]

Sound waves are longitudinal; light waves are transverse.
Sound waves require a medium to travel; light waves can travel through a vacuum.
Sound waves travel much slower than light waves.
Sound waves are mechanical waves; light waves are electromagnetic waves.
Award [1] for each valid difference.

7. (a) Distance = speed × time = 1500 × 0.80 = 1200 m (total distance travelled by sound). Distance to shoal = 1200/2 = 600 m. [2]

Award [1] for calculating total distance, [1] for halving to get one-way distance.

(b) Ultrasound has a higher frequency/shorter wavelength than audible sound, so it can detect smaller objects and produces less diffraction, giving better resolution. [1]

Accept any valid reason.

8. (a) The frequency of the vibrating string determines the pitch. [1]

(b) Amplitude: The amplitude of vibration increases. [1] Loudness: The loudness of the sound increases. [1]

9. Total distance travelled by sound = speed × time = 340 × 1.2 = 408 m. Distance to cliff = 408/2 = 204 m. [2]

Award [1] for total distance, [1] for halving.

10. (a) Time interval = 20/40 = 0.50 s [1]

(b) In 0.50 s, sound travels to the wall and back: total distance = 2 × 170 = 340 m. Speed = distance/time = 340/0.50 = 340 m/s. [2]

Award [1] for recognising total distance is 340 m, [1] for correct speed with unit.

Section C: Light (Questions 11–15)

11. (a) n = sin i / sin r = sin 45° / sin 28° = 0.7071/0.4695 = 1.51 [2]

Award [1] for correct formula, [1] for correct answer (accept 1.5).

(b) The speed of light decreases when it enters the glass. [1]

12. (a) sin c = 1/n = 1/1.33 = 0.7519; c = sin⁻¹(0.7519) = 48.8° [2]

Award [1] for correct formula, [1] for correct answer (accept 48.8° or 49°).

(b) Since the angle of incidence (55°) is greater than the critical angle (48.8°), total internal reflection occurs. All the light is reflected back into the water; no light is refracted into the air. [2]

Award [1] for stating TIR occurs, [1] for explanation referencing critical angle comparison.

13. (a) Real [1]

(b) Diminished [1]

14. (a) Total internal reflection [1]

(b) Any two from: [2]

Light must travel from a denser medium to a less dense medium (higher to lower refractive index).
The angle of incidence must be greater than the critical angle.
Award [1] for each correct condition.

Higher bandwidth/can carry more data.
Less signal loss/attenuation.
Not affected by electromagnetic interference.
Lighter and thinner than copper wires.

15. (a) 30° [1]

(b) Any two from: [2]

The image is virtual.
The image is upright.
The image is laterally inverted.
The image is the same size as the object.
The image distance equals the object distance.
Award [1] for each correct characteristic.

Section D: Electromagnetic Spectrum and Integrated Questions (Questions 16–20)

16. (a) All electromagnetic waves travel at the same speed in a vacuum (3.0 × 10⁸ m/s). [1]

(b) Gamma rays [1]

Remote controls.
Thermal imaging.
Infrared heaters.
Night vision equipment.

17. (a) λ = v/f = (3.0 × 10⁸)/(2.45 × 10⁹) = 0.122 m (or 12.2 cm) [2]

Award [1] for correct formula, [1] for correct answer with unit.

(b) The metal screen reflects microwaves, preventing them from escaping the oven and causing harm to users. [1]

Accept: The holes in the screen are smaller than the wavelength of microwaves, so microwaves cannot pass through.

18. (a) f = v/λ = (3.0 × 10⁸)/300 = 1.0 × 10⁶ Hz (or 1.0 MHz) [2]

Award [1] for correct formula, [1] for correct answer with unit.

(b) Any one from: [1]

Radio waves are electromagnetic/transverse; sound waves are mechanical/longitudinal.
Radio waves can travel through a vacuum; sound waves cannot.
Radio waves travel at 3.0 × 10⁸ m/s; sound waves travel much slower.

19. (a) Any one from: [1]

Skin cancer.
Premature ageing of skin.
Damage to eyes/cataracts.
Sunburn.

(b) Any one from: [1]

Sterilisation of medical equipment.
Detecting forged banknotes.
Production of vitamin D in the skin.
Fluorescent lamps.

20. (a) n = sin i / sin r; 1.52 = sin 60° / sin r; sin r = sin 60°/1.52 = 0.8660/1.52 = 0.5697; r = sin⁻¹(0.5697) = 34.7° [2]

Award [1] for correct formula and substitution, [1] for correct answer (accept 34.7° or 35°).

(b) The angle of incidence in the glass must be greater than the critical angle for the glass-air boundary. [1]

Accept: The ray must strike the boundary at an angle greater than the critical angle.

END OF ANSWER KEY