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A Level H1 Physics Waves Sound Light Quiz

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Questions

A-Level Physics H1 Quiz - Waves Sound Light

Name: __________________________
Class: __________________________
Date: __________________________
Score: ________ / 45

Duration: 45 minutes
Total Marks: 45

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.
Use $g = 9.81 \text{ m s}^{-2}$ , $c = 3.00 \times 10^8 \text{ m s}^{-1}$ , $h = 6.63 \times 10^{-34} \text{ J s}$ , and $e = 1.60 \times 10^{-19} \text{ C}$ where appropriate.

Section A: Wave Properties and Superposition (Questions 1–5)

1. Define the term coherence as applied to two wave sources.
[1]

2. A progressive wave has a frequency of 250 Hz and a wavelength of 1.2 m. Calculate the speed of the wave.
[2]

3. Explain why sound waves cannot be polarized, whereas light waves can.
[2]

4. Two coherent sources of sound waves interfere. At a certain point, the path difference between the waves from the two sources is 1.5 wavelengths. State whether constructive or destructive interference occurs at this point and explain your reasoning.
[2]

5. A stationary wave is formed on a string fixed at both ends. The string vibrates in its fundamental mode. (a) State the relationship between the length of the string $L$ and the wavelength $\lambda$ of the fundamental mode.
[1]

(b) If the frequency of the fundamental mode is 120 Hz, calculate the frequency of the third harmonic.
[2]

Section B: Light and Interference (Questions 6–10)

6. In a Young’s double-slit experiment, monochromatic light of wavelength $\lambda$ produces fringes of separation $x$ on a screen at distance $D$ from the slits. The slit separation is $a$ . State the formula relating these quantities.
[1]

7. Using the setup in Question 6, the slit separation $a$ is doubled while $D$ and $\lambda$ remain constant. Describe and explain the change in the fringe separation $x$ .
[2]

8. Light of wavelength 550 nm is incident normally on a diffraction grating with 500 lines per mm. Calculate the angle $\theta$ for the second-order maximum.
[3]

9. Explain why a diffraction grating produces sharper and brighter maxima compared to a double-slit arrangement.
[2]

10. White light is passed through a double-slit apparatus. Describe the appearance of the central fringe and the first-order fringes.
[2]

Section C: Photoelectric Effect (Questions 11–15)

11. Define the work function of a metal.
[1]

12. State Einstein’s photoelectric equation, defining all symbols used.
[2]

13. A metal surface has a work function of 2.3 eV. Light of frequency $8.0 \times 10^{14}$ Hz is incident on the surface. (a) Calculate the energy of a single photon of this light in Joules.
[2]

(b) Determine the maximum kinetic energy of the emitted photoelectrons in Joules.
[2]

14. In a photoelectric experiment, the intensity of the incident monochromatic light is increased while keeping the frequency constant. (a) State the effect on the maximum kinetic energy of the photoelectrons.
[1]

(b) State the effect on the photoelectric current.
[1]

15. Explain why the existence of a threshold frequency supports the particle nature of light rather than the wave nature.
[2]

Section D: Sound and Doppler Effect (Questions 16–20)

16. A sound wave travels from air into water. State what happens to: (a) the frequency of the wave.
[1]

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

17. An ambulance emits a siren of frequency 1200 Hz. It moves towards a stationary observer at a speed of 25 m s⁻¹. The speed of sound in air is 340 m s⁻¹. Calculate the frequency heard by the observer.
[3]

18. Explain why the pitch of the siren appears to drop as the ambulance passes the observer and moves away.
[2]

19. Ultrasound waves are used in medical imaging. State one property of ultrasound that makes it suitable for this application.
[1]

20. A stationary source emits sound of frequency $f_s$ . An observer moves away from the source with speed $v_o$ . The speed of sound is $v$ . Derive or state the formula for the observed frequency $f_o$ .
[2]

Answers

A-Level Physics H1 Quiz - Waves Sound Light (Answer Key)

1. Coherence means the two sources have a constant phase difference (and the same frequency).
[1]

2. Speed $v = f \lambda$
$v = 250 \times 1.2$
$v = 300 \text{ m s}^{-1}$
[1 for formula, 1 for answer]

3. Sound waves are longitudinal (vibrations parallel to direction of propagation).
[1]
Polarization requires transverse vibrations (perpendicular to direction of propagation), which light possesses.
[1]

4. Destructive interference.
[1]
Path difference is $(n + \frac{1}{2})\lambda$ (where $n=1$ ), which corresponds to waves arriving in antiphase ( $180^\circ$ or $\pi$ rad phase difference).
[1]

5. (a) $L = \frac{\lambda}{2}$ (or $\lambda = 2L$ )
[1]
(b) Frequency of $n$ -th harmonic $f_n = n f_1$ .
$f_3 = 3 \times 120 = 360 \text{ Hz}$
[1 for relationship, 1 for answer]

6. $x = \frac{\lambda D}{a}$
[1]

7. Fringe separation $x$ is halved (decreases by half).
[1]
Because $x$ is inversely proportional to slit separation $a$ ( $x \propto \frac{1}{a}$ ).
[1]

8. Grating spacing $d = \frac{1}{500 \times 10^3} \text{ m} = 2.0 \times 10^{-6} \text{ m}$ .
[1]
Formula: $d \sin \theta = n \lambda$
$\sin \theta = \frac{n \lambda}{d} = \frac{2 \times 550 \times 10^{-9}}{2.0 \times 10^{-6}}$
$\sin \theta = 0.55$
$\theta = \sin^{-1}(0.55) = 33.4^\circ$
[1 for substitution, 1 for answer]

9. More slits result in more constructive interference at the maxima positions, making them brighter/sharper.
[1]
Destructive interference is more complete between maxima, making the background darker/narrower peaks.
[1]

10. Central fringe is white.
[1]
First-order fringes are spectra (colored), with violet/blue closest to the center and red furthest (due to $\lambda_{violet} < \lambda_{red}$ ).
[1]

11. The minimum energy required to remove an electron from the surface of a metal.
[1]

12. $hf = \Phi + K_{max}$ (or $hf = \Phi + \frac{1}{2}mv_{max}^2$ )
[1]
Where $h$ is Planck's constant, $f$ is frequency, $\Phi$ is work function, $K_{max}$ is max kinetic energy.
[1]

13. (a) $E = hf = 6.63 \times 10^{-34} \times 8.0 \times 10^{14}$
$E = 5.30 \times 10^{-19} \text{ J}$
[1 for formula/sub, 1 for answer]

(b) Convert $\Phi$ to Joules: $2.3 \text{ eV} \times 1.60 \times 10^{-19} \text{ J/eV} = 3.68 \times 10^{-19} \text{ J}$ .
[1]
$K_{max} = E - \Phi = 5.30 \times 10^{-19} - 3.68 \times 10^{-19}$
$K_{max} = 1.62 \times 10^{-19} \text{ J}$
[1 for subtraction, 1 for answer]

14. (a) No change (remains constant).
[1]
(b) Increases (proportional to intensity).
[1]

15. Wave theory predicts energy depends on intensity (amplitude), so any frequency should eventually emit electrons if intense enough.
[1]
Particle theory predicts energy depends on frequency ( $E=hf$ ); if $hf < \Phi$ , no emission occurs regardless of intensity, explaining the threshold.
[1]

16. (a) Frequency remains constant.
[1]
(b) Wavelength increases (since speed increases in water and $v=f\lambda$ ).
[1]

17. Formula for source moving towards observer: $f_o = f_s \left( \frac{v}{v - v_s} \right)$
[1]
$f_o = 1200 \left( \frac{340}{340 - 25} \right)$
$f_o = 1200 \left( \frac{340}{315} \right)$
$f_o = 1295 \text{ Hz}$ (or 1300 Hz to 2 s.f.)
[1 for substitution, 1 for answer]

18. As the ambulance moves away, the wavelength is stretched (increases).
[1]
Since $v = f\lambda$ and $v$ is constant, an increase in $\lambda$ leads to a decrease in frequency (pitch).
[1]

19. High frequency / Short wavelength allows for high resolution imaging.
[1]
(Alternatively: It is non-ionizing / safe for tissue).

20. $f_o = f_s \left( \frac{v - v_o}{v} \right)$
[2]
(1 mark for correct numerator $v - v_o$ indicating moving away, 1 mark for correct structure).