# Question: A method of determining the focal length of a diverging

A method of determining the focal length of a diverging lens is called auto collimation. As Fig. 23.30 shows, first a sharp image of a light source is projected onto a screen by a converging lens. Second, the screen is replaced with a plane mirror. Third, a diverging lens is placed between the converging lens and the mirror. Light will then be reflected by the mirror back through the compound-lens system, and an image will be formed on a screen near the light source. This image is sharpened by adjusting the distance between the diverging lens and the mirror. The distance at which the image is clearest is equal to the focal length of the lens. Explain why this method works.

## Answer to relevant Questions

For the arrangement shown in Fig. 23.31, an object is placed 0.40 m in front of the converging lens, which has a focal length of 0.15 m. If the concave mirror has a focal length of 0.13 m, where is the final image formed, ...Prove that do = |di| (equal magnitude) for a plane mirror. (a) Derive a relationship that gives the locations of the minima in a Young’s double-slit experiment. What is the distance between adjacent minima? (b) For a third-order minimum (the third side dark position from the ...In the development of Young’s double-slit experiment, a small-angle approximation (tan θ ≈ sin θ) was used to find the lateral displacements of the maxima (bright) and minima (dark) positions. How good is this ...A slit of width 0.20 mm is illuminated with monochromatic light of wavelength 480 nm, and a diffraction pattern is formed on a screen 1.0 m from the slit. (a) What is the width of the central maximum? (b) What are the ...Post your question