Light in Communication and Technology
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Light in Communication and Technology — Free MYP4 Physics Practice Questions

1QuestionFiber Optics and Total Internal ReflectionConcept Practice
2 marks~3 minCriterion D
Fiber optic cables transmit light signals by total internal reflection. Internet providers use fiber optics to deliver high-speed broadband, yet coverage remains uneven across different regions.
a
Identify one real-world application of fiber optic cables beyond internet provision. [1]
b
Explain one reason why fiber optic cables are difficult to deploy for internet access in rural communities. [1]
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2QuestionLasers and Optical DevicesAssessment Practice
5 marks~8 minCriterion C
A laser beam travels from air into an unknown transparent medium. The angles of incidence θ1\theta_1 (in air) and refraction θ2\theta_2 (in the medium) are measured across several trials and plotted as sin⁡θ2\sin\theta_2 versus sin⁡θ1\sin\theta_1. The graph is a straight line through the origin with gradient 0.6670.667.

Snell's law: n1sin⁡θ1=n2sin⁡θ2n_1 \sin\theta_1 = n_2 \sin\theta_2, where n1=1.00n_1 = 1.00 for air.

Refractive indices of candidate media:
Crown glass: 1.52 — Flint glass: 1.62 — Diamond: 2.42 — Water: 1.33
a
Deduce the relationship between the gradient of the graph and the refractive index n2n_2 of the medium. [1]
b
Calculate the refractive index of the medium. [2]
c
A technician claims the medium is crown glass. Evaluate this claim using your calculated value and the data provided. [2]
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3QuestionDigital vs Analog Signals IntroductoryConcept Practice
2 marks~3 minCriterion A
The diagram shows two electrical signals plotted on voltage–time axes.

Signal X is a smooth, continuous wave that varies sinusoidally between −5 V-5\ \text{V} and +5 V+5\ \text{V}.

Signal Y alternates sharply between exactly 0 V0\ \text{V} and 5 V5\ \text{V}.
a
Identify which signal is digital. [1]
b
State one characteristic of digital signals that distinguishes them from analog signals. [1]
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4QuestionAssessment Practice
6 marks~9 minCriterion D

Data

Distance (m)12345
Measured signal (dBm)−30-30−38-38−44-44−49-49−53-53
In satellite communication, a phone transmits at 2.4 GHz. Signal strength follows the inverse-square law, Pr∝1d2P_r \propto \frac{1}{d^2}, where dd is distance from the transmitter. In decibels, the change in signal strength relative to 1 m is given by ΔS=10log⁡10 ⁣(1d2)\Delta S = 10\log_{10}\!\left(\frac{1}{d^2}\right) dB. The signal strength at 1 m is −30-30 dBm.

Measured
a
Calculate the theoretical signal strength (dBm) at distances of 2 m, 3 m, 4 m, and 5 m. [2]
b
Deduce the percentage deviation of the measured signal from the theoretical value at each distance using:
deviation=measured−theoretical∣theoretical∣×100%\text{deviation} = \frac{\text{measured} - \text{theoretical}}{\lvert\text{theoretical}\rvert} \times 100\% [2]
c
Evaluate the validity of the inverse-square law as a model for this data, identifying at least one physical reason for any systematic trend in the deviations. [2]
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5QuestionFiber Optics and Total Internal ReflectionAssessment Practice
8 marks~12 minCriterion A
An optical fibre carries light signals through a glass core (refractive index ncore=1.52n_{\text{core}} = 1.52) surrounded by cladding (refractive index nclad=1.39n_{\text{clad}} = 1.39).
a
State the two conditions required for total internal reflection to occur at the core–cladding boundary. [2]
b
Construct a ray diagram showing light undergoing total internal reflection inside the optical fibre. Label the core, cladding, angle of incidence θi\theta_i, and angle of reflection θr\theta_r. [2]
c
Explain how total internal reflection allows an optical fibre to transmit communication signals over long distances with minimal signal loss. [2]
d
The critical angle θc\theta_c for this fibre is given by sin⁡θc=ncladncore\sin\theta_c = \dfrac{n_{\text{clad}}}{n_{\text{core}}}. Calculate θc\theta_c and analyse whether a ray striking the boundary at 68° will undergo total internal reflection. [2]
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