Question

1. A Helium discharge lamp gives off two wavelengths 651 nm and 484 nm. The diffraction grating has 406 lines/mm that is observered on a screen that is 1.20 m away. What is the distance between the first order fringes of the two different wavelengths?

1.88 m
0.0884 m
1.18 m
4.94×10^-10 m

2.

An object is 17.0 cm from a converging lens and the object is 0.600 cm tall. What is the position and height of the image if the focal length of the lens is 60.0 cm?

The object is at -23.7 cm and the height of the image will be 0.00149 cm inverted.
The object is at -23.7 cm and the height of the image will be 0.836 cm upright.
The object is at -0.0422 cm and the height of the image will be 0.836 cm inverted.
The object is at -0.0422 cm and the height of the image will be 0.00149 cm upright.

Answer 1

In a diffraction grating "angular position of fringe of order m and wave length λ d L postion of m bright fringe from the centre of screen ya (a) Numberof slits N meter 406/mm 406 e +03/m slit width .d-i- the seperation between first order wavelength λ,-651 nm and λ,-484 nm-Δy mAL m is theorder,1-distancefrom grating to screen=1.2m -2.463e-06m N 406 x103 /m AL λ.L by=y, substituting all the know values gives Δy 0.0 884m 2) if so and si arethe object distance andits image distances from the lense we usethethinlensformula SO S f- focal length of thelens 60.0 cm 60.0cm 17.0 si we plug the values in hand whileusing therelationgiveus > | Sİ--23. 7 cm l image distance magnification of lens-m we usetherelation i_23.72cm so 17.0cm hi 1.395 1o ->hi-0.836cm The object is at- 23.7 cm and the height of the image will be 0.836 cm upright