O Level Physics Waves Sound Light Quiz

O-Level Physics Quiz - Waves Sound Light - ANSWER KEY

Total Marks: 40

Section A: General Wave Properties [10 marks]

1. Wave on a rope

(a) Amplitude = 2.0 cm [1]

• Accept: 2 cm
• Mark: 1 mark for correct value with unit

(b) Wavelength = 40 cm [1]

• Accept: 0.40 m
• Mark: 1 mark for correct value with unit (distance between two consecutive crests/troughs)

(c) Speed calculation:

• v = f × λ
• v = 5.0 × 0.40 = 2.0 m/s
• OR v = 5.0 × 40 = 200 cm/s [2]
• Mark scheme:
  • 1 mark for correct formula v = fλ
  • 1 mark for correct answer with unit (2.0 m/s or 200 cm/s)

2. Ripple tank - deep to shallow water

(a) The speed decreases [1]

• Mark: 1 mark for stating speed decreases

(b) Explanation:

• v = fλ, and frequency (f) remains constant [1]
• Since speed (v) decreases, wavelength (λ) must also decrease proportionally [1]
• Mark scheme:
  • 1 mark for referencing v = fλ and constant frequency
  • 1 mark for linking decreased speed to decreased wavelength

3. Transverse vs longitudinal waves

Transverse waves:

• Particles vibrate perpendicular to the direction of wave travel
• Example: light waves / water waves / waves on a rope / any EM wave [1.5]

Longitudinal waves:

• Particles vibrate parallel to the direction of wave travel
• Example: sound waves / ultrasound / seismic P-waves [1.5]

Mark scheme:

• 1 mark for correct description of transverse wave vibration direction
• 0.5 mark for correct transverse example
• 1 mark for correct description of longitudinal wave vibration direction
• 0.5 mark for correct longitudinal example

4. Ripple tank wave calculation

(a) Speed calculation:

• v = f × λ
• v = 12 × 2.0 = 24 cm/s (or 0.24 m/s) [2]
• Mark scheme:
  • 1 mark for correct formula v = fλ
  • 1 mark for correct answer with unit

(b) Ways to change speed:

• Change the depth of the water [1]
• Use a different liquid (change the medium) [1]
• Mark: 1 mark each for any two valid methods

5. Slinky spring wave

(a) Type of wave: Longitudinal wave [1]

• Mark: 1 mark for correct identification

(b) Producing a transverse wave:

• Move one end of the slinky up and down (or side to side) perpendicular to the length of the spring [1]
• Mark: 1 mark for describing perpendicular displacement of the end

Section B: Sound [10 marks]

6. Echo calculation

(a) Distance calculation:

• Total distance travelled by sound = speed × time
• Total distance = 340 × 0.60 = 204 m
• Distance to wall = 204 ÷ 2 = 102 m [2]
• Mark scheme:
  • 1 mark for calculating total distance (204 m)
  • 1 mark for dividing by 2 to get distance to wall (102 m)

(b) Explanation:

• Sound energy spreads out over a larger area / some energy is absorbed by the wall and air [1]
• Mark: 1 mark for any valid reason (energy spreading, absorption, or both)

7. Loudspeaker sound wave

(a) Wavelength calculation:

• λ = v / f
• λ = 340 / 680 = 0.50 m [2]
• Mark scheme:
  • 1 mark for correct formula λ = v/f
  • 1 mark for correct answer with unit (0.50 m or 50 cm)

(b) Effect on loudness:

• The sound becomes louder [1]
• Explanation: A larger amplitude means more energy is transferred by the wave per unit time, resulting in greater loudness [1]
• Mark scheme:
  • 1 mark for stating sound becomes louder
  • 1 mark for linking amplitude to energy transfer and loudness

8. Ultrasound

(a) Frequency range: Above 20 000 Hz (or above 20 kHz) [1]

• Mark: 1 mark for correct lower bound (accept "above 20 kHz" or "above 20 000 Hz")

(b) Suitability for medical scanning:

• Ultrasound has very short wavelengths, allowing it to produce detailed images of small structures [1]
• Ultrasound can penetrate body tissues and reflect from boundaries between different tissues/organs, enabling imaging without harmful ionising radiation [1]
• Mark scheme:
  • 1 mark for short wavelength / high resolution
  • 1 mark for penetration and reflection from tissue boundaries OR non-ionising/safe nature

9. Sonar calculation

(a) Distance calculation:

• Total distance = speed × time = 1500 × 0.80 = 1200 m
• Distance to shoal = 1200 ÷ 2 = 600 m [2]
• Mark scheme:
  • 1 mark for calculating total distance (1200 m)
  • 1 mark for dividing by 2 to get distance to shoal (600 m)

10. Guitar string

(a) Pitch determinant:

• The frequency of the vibrating string (or frequency of the sound wave) [1]
• Mark: 1 mark for stating frequency

(b) Effect of tightening:

• Tightening the string increases the tension, which increases the frequency of vibration [1]
• A higher frequency produces a higher pitch [1]
• Mark scheme:
  • 1 mark for linking increased tension to increased frequency
  • 1 mark for linking increased frequency to higher pitch

Section C: Light [20 marks]

11. Refraction in glass block

(a) Refractive index definition:

• The ratio of the speed of light in vacuum (or air) to the speed of light in the medium [1]
• Mark: 1 mark for correct definition (accept "n = c/v" or equivalent wording)

(b) Angle of refraction calculation:

• n = sin i / sin r
• 1.5 = sin 45° / sin r
• sin r = sin 45° / 1.5 = 0.7071 / 1.5 = 0.4714
• r = sin⁻¹(0.4714) = 28.1° (or 28°) [2]
• Mark scheme:
  • 1 mark for correct substitution into n = sin i / sin r
  • 1 mark for correct answer (28° or 28.1°)

(c) Ray diagram:

• Ray bends towards the normal on entering glass [0.5]
• Angle of refraction labelled correctly [0.5]
• Ray travels straight through glass [0.5]
• Ray bends away from normal on exiting, emerging parallel to incident ray [0.5]
• Mark: 2 marks total as indicated

12. Total internal reflection

(a) Critical angle definition:

• The angle of incidence in the denser medium for which the angle of refraction in the less dense medium is 90° [1]
• Mark: 1 mark for correct definition

(b) Description and explanation:

• Total internal reflection occurs [1]
• Explanation: The angle of incidence (50°) is greater than the critical angle (48°), so the light is completely reflected back into the water rather than being refracted into the air [1]
• Mark scheme:
  • 1 mark for stating total internal reflection occurs
  • 1 mark for explaining that angle of incidence exceeds critical angle

(c) Application:

• Optical fibres (in telecommunications/medicine) / endoscopes / periscopes using prisms / bicycle reflectors [1]
• Mark: 1 mark for any valid application

13. Converging lens calculation

(a) Image distance calculation:

• 1/f = 1/u + 1/v
• 1/15 = 1/25 + 1/v
• 1/v = 1/15 - 1/25 = (5 - 3)/75 = 2/75
• v = 75/2 = 37.5 cm [2]
• Mark scheme:
  • 1 mark for correct substitution into lens formula
  • 1 mark for correct answer with unit (37.5 cm)

(b) Image characteristics:

• Real [1]
• Inverted [1]
• Magnified (larger than object) [1]
• Mark: 1 mark each for any three correct characteristics (real, inverted, magnified/enlarged)

14. Magnifying glass

(a) Object position:

• The insect must be placed between the lens and its focal point (i.e., at a distance less than the focal length from the lens) [1]
• Mark: 1 mark for correct position (u < f)

(b) Ray diagram:

• Correct lens symbol with principal axis [0.5]
• Focal points (F and F') labelled on both sides [0.5]
• Object (insect) placed between F and lens, labelled [0.5]
• Two construction rays drawn correctly:
  • Ray parallel to axis, refracted through F' [0.5]
  • Ray through optical centre, undeviated [0.5]
• Virtual image shown on same side as object, upright and magnified, labelled [0.5]
• Mark: 3 marks total

(c) Effect of shorter focal length:

• A lens with shorter focal length produces greater magnification when used as a magnifying glass [1]
• Explanation: Magnification = 25/f (approx.) or the object can be brought closer to the lens while still being within the focal length, producing a larger virtual image [1]
• Mark scheme:
  • 1 mark for stating magnification increases
  • 1 mark for valid explanation (shorter f means object can be closer / larger angular magnification)

15. Plane mirror

(a) Angle of reflection:

• Angle of reflection = 30° [1]
• Mark: 1 mark for correct value (equal to angle of incidence)

(b) Image characteristics:

• Virtual [1]
• Same size as object / laterally inverted / same distance behind mirror as object is in front [1]
• Mark: 1 mark each for any two correct characteristics

Section D: Electromagnetic Waves [10 marks]

16. Properties of EM waves

• They all travel at the same speed in a vacuum (3.0 × 10⁸ m/s) [1]
• They are all transverse waves / they can travel through a vacuum / they transfer energy [1]
• Mark: 1 mark each for any two correct properties

17. Radio wave calculation

(a) Wavelength calculation:

• λ = v / f
• λ = (3.0 × 10⁸) / (100 × 10⁶) = 3.0 m [2]
• Mark scheme:
  • 1 mark for correct formula λ = v/f
  • 1 mark for correct answer with unit (3.0 m)

18. Infrared radiation

(a) Use of infrared:

• Thermal imaging / heating / cooking / night vision / data transmission (optical fibres) [1]
• Mark: 1 mark for any valid use

(b) Suitability for remote controls:

• Infrared is invisible to the human eye / does not interfere with visible light / can be modulated to carry information / is easily detected by electronic sensors [1]
• Mark: 1 mark for any valid reason

19. X-rays

(a) Property for medical imaging:

• X-rays can penetrate soft tissue but are absorbed by bone / have short wavelengths enabling high resolution [1]
• Mark: 1 mark for any valid property

(b) Safety precaution:

• Limit exposure time / use lead shielding / stand behind a protective screen / wear a dosimeter badge [1]
• Mark: 1 mark for any valid precaution

20. Refractive index calculation

(a) Refractive index calculation:

• n = sin i / sin r
• n = sin 60° / sin 40°
• n = 0.8660 / 0.6428 = 1.35 (or 1.3) [2]
• Mark scheme:
  • 1 mark for correct formula and substitution
  • 1 mark for correct answer (1.35 or 1.3)

END OF ANSWER KEY