AQA ยท A level Physics

Optical horizon waves and energy A-level challenge

Can you get 100%? Use an optical-fibre black-hole analogue to test refractive index, wavelength, photon energy and conservation of energy.

Read about the optical Hawking-radiation analogue

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Question

7 marks

Answer all parts. Show your working and give units where appropriate.

1(a)

An optical fibre has refractive index 1.50. Calculate the speed of light in the fibre. Use c = 3.00 x 10^8 m s^-1.

[2 marks]

1(b)

Probe light has frequency 3.75 x 10^14 Hz. Calculate its wavelength inside the fibre.

[2 marks]

1(c)

A travelling pump pulse changes the refractive index and creates a boundary that probe light cannot cross in one direction. The probe stimulates an additional paired light component, and the pump spectrum changes at the same time. Explain why the changed pump spectrum is evidence for backreaction and why the experiment does not break conservation of energy.

[3 marks]

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