2021 Physics Prelim Year 4 SJI P2 Section B

15 CANDIDATE NAME CLASS INDEX NUMBER Section B Q10 Q11 Q12E Q12O Section B (30 marks) Answer all questions in this section. Answer only one of two alternative questions in Question 12. 10 Optical fibre is used extensively to transmit internet data around the world, as an estimated 2.5 x 109 Gigabytes of data is created and accessed each day. Fig. 10.1 shows a cross-sectional view of an optical fibre used for such data transmission. Internet data, in the form of light ray travels through the cylindrical glass core, that is surrounded by a layer of cladding. A light ray enters from air into the core at point P. Fig. 10.1 (not to scale) claddingcoreRSnormalPlight ray12⁰airQTU

16 During the design of a particular optical fibre, various materials for the core and cladding are considered. Fig. 10.2 shows a list of materials, and their refractive indices. Fig. 10.2 (a) State what is meant by the term critical angle. ……………………………………………………………………………..…………... ………………………………………………………………………………..………... ..…………………………………….………………………………………………..[1] (b) One of the core materials from Fig. 10.2 is being considered. A ray of light that enters at P with an angle of incidence of 12o travels into this core, and subsequently makes an angle of incidence along surface MN at 82o. Assuming that the cross section of the core RSTU is a rectangle, calculate the refractive index of this core material, and identify the material chosen by referring to Fig. 10.2. core material = ……………………….. [2] (c) Next, material C is being considered for the core, with the same light ray entering P at an angle of incidence of 12o. (i) Calculate the speed of light that travels through C. speed = ……………………….. [2] Core materialRefractive indexA1 . 5 3B1 . 4 9C1 . 4 0D1 . 4 2E1 . 5 6Cladding materialRefractive indexV1 . 4 4W1 . 4 1X1 . 3 6Y1 . 5 2Z1 . 5 0

17 (ii) From Fig. 10.2, select a suitable cladding to be used with C. Using ideas about angle of incidence, critical angle, and refractive index, explain how your selection of cladding allows a ray of light travelling from P to Q to be reflected off RS. …………………………………………………..……………………………... ………………………………………………..………………………………... ……………………………………………………..…………………………... …………………………………….………………..………………………..[2] (iii) A student suggests that the critical angle (θc) of light for C in (c)(ii) can be obtained by applying the formula: where n is the refractive index of material C. Provide a reason why the student’s suggestion cannot be used here. ……………………………………………..…………………………………... ……………………………………………...………………………………..[1] (iv) Two different incident rays, R1 and R2, enter material C at the same point P. R1 has a lower angle of incidence than R2, and both rays reflect off RS. Compar