Figure 2 shows a ray of monochromatic green light incident normally on the curved surface of a semicircular glass block - AQA - A-Level Physics - Question 3 - 2017 - Paper 1
Question 3
Figure 2 shows a ray of monochromatic green light incident normally on the curved surface of a semicircular glass block.
The angle of refraction of the ray at the p... show full transcript
Worked Solution & Example Answer:Figure 2 shows a ray of monochromatic green light incident normally on the curved surface of a semicircular glass block - AQA - A-Level Physics - Question 3 - 2017 - Paper 1
Step 1
The angle of incidence of the ray on the flat surface of the block.
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Answer
To calculate the angle of incidence, we can apply Snell's law, which states:
n1sin(θ1)=n2sin(θ2)
Given that:
Refractive index of glass (n1) = 1.6
Angle of refraction (θ2) = 90°
This allows us to calculate:
sin(θ1)=n1n2sin(θ2)=1.61⋅1=0.625
Thus, we find that:
θ1=arcsin(0.625)≈39°
So, the angle of incidence is approximately 39 degrees.
Step 2
Calculate the refractive index of the liquid.
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Answer
Using Snell's law again for the glass-liquid interface:
nglasssin(58°)=nliquidsin(90°)
Here, we know:
Refractive index of glass (nglass) = 1.6
Angle of incidence = 58°
Therefore,
1.6sin(58°)=nliquid⋅1
Calculate sin(58°)≈0.848:
nliquid=1.6⋅0.848≈1.36
Thus, the refractive index of the liquid is approximately 1.36.
Step 3
Describe and explain the paths followed by the red and blue rays immediately after the light is incident on the glass–liquid interface.
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Answer
At the glass-liquid interface, red light undergoes total internal reflection (TIR) while blue light refracts through. This phenomenon occurs because:
The critical angle for red light is higher than for blue light, hence under TIR conditions, red light cannot pass through and is reflected back into the glass.
Blue light, with a lower refractive index, refracts into the liquid therefore bending away from the normal.
To summarize, the red light maintains its path within the glass, while the blue light bends and passes into the liquid, demonstrating a clear distinction in behavior based on their respective refractive indices.
