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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: 50 minutes
Total Marks: 45

Instructions:

Answer all questions.
Write your answers in the spaces provided.
Show all working clearly. Marks are awarded for correct reasoning and steps, not just the final answer.
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: Multiple Choice & Short Concepts (Questions 1–5)

1. Which of the following statements correctly describes the nature of sound waves and light waves in air?

A. Sound is longitudinal; Light is longitudinal.
B. Sound is transverse; Light is transverse.
C. Sound is longitudinal; Light is transverse.
D. Sound is transverse; Light is longitudinal.

[1]

2. A wave has a frequency of $500 \text{ Hz}$ and a wavelength of $0.68 \text{ m}$ . What is the speed of the wave?

A. $340 \text{ m s}^{-1}$
B. $735 \text{ m s}^{-1}$
C. $0.00136 \text{ m s}^{-1}$
D. $290 \text{ m s}^{-1}$

[1]

3. In a double-slit interference experiment, the fringe separation $x$ is given by $x = \frac{\lambda D}{a}$ . If the distance $D$ from the slits to the screen is doubled and the slit separation $a$ is halved, what is the new fringe separation in terms of the original $x$ ?

A. $0.25 x$
B. $0.5 x$
C. $2 x$
D. $4 x$

[1]

4. State the condition required for two sources of light to produce a stable interference pattern.

[1]

5. Define the term work function in the context of the photoelectric effect.

[1]

Section B: Structured Problems (Questions 6–15)

6. A stationary wave is formed on a string fixed at both ends. The length of the string is $1.2 \text{ m}$ .

(a) Determine the wavelength of the fundamental mode (first harmonic).

[2]

(b) If the speed of the wave on the string is $24 \text{ m s}^{-1}$ , calculate the frequency of the fundamental mode.

[2]

7. Light of wavelength $550 \text{ nm}$ is incident normally on a diffraction grating with $500$ lines per mm.

(a) Calculate the grating spacing $d$ in metres.

[2]

(b) Determine the angle $\theta$ for the second-order maximum.

[3]

8. In a photoelectric effect experiment, a metal surface is illuminated with ultraviolet light of wavelength $250 \text{ nm}$ . The work function of the metal is $3.2 \text{ eV}$ .

(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.

[3]

9. Explain why the photoelectric effect provides evidence for the particle nature of light, specifically referring to the concept of threshold frequency.

[3]

10. A sound wave travels from air into water. The frequency of the wave remains constant.

(a) State what happens to the speed of the sound wave.

[1]

(b) State what happens to the wavelength of the sound wave.

[1]

11. Two coherent sound sources $S_1$ and $S_2$ emit waves of wavelength $0.50 \text{ m}$ . A detector is placed at a point $P$ such that the distance $S_1P = 2.00 \text{ m}$ and $S_2P = 2.75 \text{ m}$ .

(a) Calculate the path difference between the two waves at point $P$ .

[1]

(b) Determine whether constructive or destructive interference occurs at point $P$ . Explain your answer.

[2]

12. The graph below shows the variation of displacement with time for a particle in a wave.

(Imagine a sinusoidal graph starting at 0, reaching max positive displacement at $t=0.02\text{ s}$ , crossing zero at $t=0.04\text{ s}$ , max negative at $t=0.06\text{ s}$ , and returning to zero at $t=0.08\text{ s}$ .)

(a) Determine the period $T$ of the wave.

[1]

(b) Calculate the frequency $f$ of the wave.

[2]

13. A laser beam passes through a single slit of width $0.10 \text{ mm}$ . A diffraction pattern is observed on a screen $2.0 \text{ m}$ away.

(a) Describe the appearance of the central maximum compared to the secondary maxima.

[2]

(b) If the width of the slit is decreased, state and explain the effect on the width of the central maximum.

[2]

14. In an experiment to determine the speed of sound, a student uses a resonance tube. The first resonance occurs when the length of the air column is $0.15 \text{ m}$ and the second resonance occurs at $0.49 \text{ m}$ . The frequency of the tuning fork is $500 \text{ Hz}$ .

(a) Determine the wavelength of the sound wave using the difference in resonance lengths.

[2]

(b) Calculate the speed of sound determined by this experiment.

[2]

15. Monochromatic light of wavelength $600 \text{ nm}$ is incident on a metal surface. No photoelectrons are emitted.

(a) Explain why no photoelectrons are emitted.

[2]

(b) Suggest one change to the incident light that would cause photoelectrons to be emitted, assuming the intensity remains constant.

[1]

Section C: Data Analysis & Extended Response (Questions 16–20)

16. A student investigates the relationship between the frequency $f$ of incident light and the maximum kinetic energy $K_{\max}$ of photoelectrons. The results are plotted on a graph of $K_{\max}$ (y-axis) against $f$ (x-axis).

(a) State the physical significance of the gradient of this graph.

[1]

(b) State the physical significance of the x-intercept of this graph.

[1]

17. Consider the equation for the photoelectric effect: $hf = \Phi + K_{\max}$ .

(a) Rearrange the equation to make $K_{\max}$ the subject.

[1]

(b) If the frequency $f$ is doubled, does the maximum kinetic energy $K_{\max}$ double? Explain your answer.

[2]

18. In a Young’s double-slit experiment, red light ( $\lambda = 650 \text{ nm}$ ) produces fringes with a separation of $2.4 \text{ mm}$ . The experiment is repeated with blue light ( $\lambda = 450 \text{ nm}$ ) using the same apparatus (same $D$ and $a$ ).

Calculate the new fringe separation.

[3]

19. A sound source emits waves uniformly in all directions. At a distance of $2.0 \text{ m}$ from the source, the intensity is $I_0$ .

(a) State the relationship between intensity $I$ and distance $r$ from a point source.

[1]

(b) Calculate the intensity at a distance of $6.0 \text{ m}$ in terms of $I_0$ .

[2]

20. Explain the difference between progressive waves and stationary waves in terms of energy transfer.

[3]

Answers

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

1. C
[1] Sound requires a medium and oscillates parallel to propagation (longitudinal). Light is an electromagnetic wave and oscillates perpendicular to propagation (transverse).

2. A
[1] $v = f \lambda = 500 \times 0.68 = 340 \text{ m s}^{-1}$ .

3. D
[1] $x \propto \frac{D}{a}$ . If $D \to 2D$ and $a \to 0.5a$ , then $x_{new} \propto \frac{2D}{0.5a} = 4 \frac{D}{a} = 4x$ .

4. The sources must have a constant phase difference (or be coherent).
[1]

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

6.
(a) For the fundamental mode, $L = \frac{\lambda}{2}$ .
$\lambda = 2L = 2 \times 1.2 = 2.4 \text{ m}$ .
[2] (1 mark for formula/relation, 1 mark for answer)

(b) $v = f \lambda \Rightarrow f = \frac{v}{\lambda}$ .
$f = \frac{24}{2.4} = 10 \text{ Hz}$ .
[2] (1 mark for substitution, 1 mark for answer)

7.
(a) $d = \frac{1}{N}$ .
$N = 500 \text{ lines/mm} = 500,000 \text{ lines/m}$ .
$d = \frac{1}{500,000} = 2.0 \times 10^{-6} \text{ m}$ .
[2] (1 mark for conversion/formula, 1 mark for answer)

(b) $d \sin \theta = n \lambda$ .
$n=2$ , $\lambda = 550 \times 10^{-9} \text{ m}$ .
$\sin \theta = \frac{2 \times 550 \times 10^{-9}}{2.0 \times 10^{-6}} = \frac{1100 \times 10^{-9}}{2.0 \times 10^{-6}} = 0.55$ .
$\theta = \sin^{-1}(0.55) \approx 33.4^\circ$ .
[3] (1 mark for formula, 1 mark for substitution, 1 mark for answer)

8.
(a) $E = \frac{hc}{\lambda}$ .
$E = \frac{6.63 \times 10^{-34} \times 3.00 \times 10^8}{250 \times 10^{-9}}$ .
$E = \frac{1.989 \times 10^{-25}}{2.5 \times 10^{-7}} = 7.956 \times 10^{-19} \text{ J}$ .
[2] (1 mark for formula/substitution, 1 mark for answer)

(b) Work function $\Phi = 3.2 \text{ eV} = 3.2 \times 1.60 \times 10^{-19} = 5.12 \times 10^{-19} \text{ J}$ .
$K_{\max} = E - \Phi$ .
$K_{\max} = 7.956 \times 10^{-19} - 5.12 \times 10^{-19} = 2.836 \times 10^{-19} \text{ J}$ .
Answer: $2.84 \times 10^{-19} \text{ J}$ (3 s.f.).
[3] (1 mark for converting $\Phi$ , 1 mark for subtraction, 1 mark for final answer)

Wave theory predicts that energy accumulates over time, so there should be a time delay before emission, especially at low intensities.
Experiment shows emission is instantaneous if $f > f_0$ .
Wave theory predicts any frequency should cause emission if intensity is high enough.
Experiment shows a threshold frequency below which no emission occurs, regardless of intensity. This supports the particle (photon) model where energy is quantized ( $E=hf$ ).
[3] (1 mark for time delay argument, 1 mark for threshold frequency argument, 1 mark for linking to particle nature)

10.
(a) Speed increases (sound travels faster in water than air).
[1]
(b) Wavelength increases ( $v = f\lambda$ , $f$ constant, $v$ increases $\Rightarrow \lambda$ increases).
[1]

11.
(a) Path difference $= |S_2P - S_1P| = |2.75 - 2.00| = 0.75 \text{ m}$ .
[1]
(b) $\frac{\text{Path Difference}}{\lambda} = \frac{0.75}{0.50} = 1.5$ .
This is $(n + \frac{1}{2})\lambda$ where $n=1$ .
Therefore, destructive interference occurs.
[2] (1 mark for ratio/calculation, 1 mark for conclusion with reason)

12.
(a) Period $T = 0.08 \text{ s}$ (time for one complete cycle).
[1]
(b) $f = \frac{1}{T} = \frac{1}{0.08} = 12.5 \text{ Hz}$ .
[2] (1 mark for formula, 1 mark for answer)

13.
(a) The central maximum is wider (twice the width of secondary maxima) and much brighter/more intense than the secondary maxima.
[2] (1 mark for width, 1 mark for intensity)
(b) The width of the central maximum increases.
Explanation: Angular width $\theta \approx \frac{\lambda}{b}$ . As slit width $b$ decreases, $\theta$ increases.
[2] (1 mark for state, 1 mark for explanation)

14.
(a) Distance between consecutive resonances $= \frac{\lambda}{2}$ .
$\frac{\lambda}{2} = 0.49 - 0.15 = 0.34 \text{ m}$ .
$\lambda = 0.68 \text{ m}$ .
[2] (1 mark for difference, 1 mark for $\lambda$ )
(b) $v = f \lambda = 500 \times 0.68 = 340 \text{ m s}^{-1}$ .
[2] (1 mark for formula, 1 mark for answer)

15.
(a) The energy of the incident photons ( $hf$ ) is less than the work function ( $\Phi$ ) of the metal.
[2] (1 mark for comparing energy/frequency, 1 mark for work function reference)
(b) Increase the frequency (or decrease the wavelength) of the light.
[1]

16.
(a) Planck’s constant $h$ .
[1]
(b) Threshold frequency $f_0$ .
[1]

17.
(a) $K_{\max} = hf - \Phi$ .
[1]
(b) No.
$K_{\max} = h(2f) - \Phi = 2hf - \Phi$ .
Doubling $K_{\max}$ would require $2(hf - \Phi) = 2hf - 2\Phi$ .
Since $\Phi$ is constant and non-zero, $2hf - \Phi \neq 2hf - 2\Phi$ . The kinetic energy increases by more than double (if $hf > \Phi$ ) or simply does not scale linearly because of the constant subtraction of $\Phi$ .
[2] (1 mark for "No", 1 mark for correct algebraic reasoning)

18.
$x = \frac{\lambda D}{a}$ . Since $D$ and $a$ are constant, $x \propto \lambda$ .
$\frac{x_{blue}}{x_{red}} = \frac{\lambda_{blue}}{\lambda_{red}}$ .
$x_{blue} = 2.4 \text{ mm} \times \frac{450}{650}$ .
$x_{blue} = 2.4 \times 0.6923 \approx 1.66 \text{ mm}$ .
[3] (1 mark for proportionality, 1 mark for substitution, 1 mark for answer)

19.
(a) $I \propto \frac{1}{r^2}$ (Inverse square law).
[1]
(b) $\frac{I_2}{I_1} = (\frac{r_1}{r_2})^2$ .
$I_2 = I_0 \times (\frac{2.0}{6.0})^2 = I_0 \times (\frac{1}{3})^2 = \frac{I_0}{9}$ .
Answer: $0.11 I_0$ or $\frac{1}{9} I_0$ .
[2] (1 mark for ratio setup, 1 mark for answer)

20.

In a progressive wave, energy is transferred from the source outwards through the medium.
In a stationary wave, there is no net transfer of energy along the wave; energy is stored in the loops (antinodes).
[3] (1 mark for progressive description, 1 mark for stationary description, 1 mark for clarity/distinction)