In a scene from a movie, a nearsighted character removes his eyeglasses and uses

Question

In a scene from a movie, a nearsighted character removes his eyeglasses and uses them to focus the nearly parallel rays of the sun to start a fire. What is physically wrong with this scene? 6. A. The eyeglasses have converging lenses and cannot be used to focus parallel rays B. The eyeglasses have diverging lenses and cannot be used to focus parallel rays C. Sunlight cannot be used to start a fire. D. A fire can only be started if the image is virtual E. Parallel rays cannot be focused. In two separate double slit experiments, an interference pattern is observed on a screen. In the first experiment, violet light ( 708 nm) is used and a second-order (second from center) bright fringe occurs at the same location as a third-order (third) dark fringe in the second experiment. Determine the wavelength of the light used in the second experiment. 7. A 1320 nm B. 862 nmm C. 503 nm D. 566 nm E 495 nm

Explanation / Answer

6. nearsightedness , also called myopia is the condition when eye lens cannot focus the light rays on the retina but does that infront of the retina

so, the light rays before entering eyelens need to diverge a bit so as to cause focus of the eyelens to shift on the retina

hence a diverging lens is used for nearsightedness

hence in the movie scene this lens which is diverging in nature cannot be used to focus light rays on a peice of paper to start fire

opiton B

7. lambda1 = 708 nm

lambda2 = ?

now, given second order bright fringe is at the same location as the third order dark fringe from the second experiment

hence

2*lambda1/d = 5*lambda2/2d

hence

lambda2 = 4*lambda1/5 = 566.4 nm

option D.

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