Final answer:
A nearsighted man with a clear vision limit of 20 cm must stand 10 cm away from the mirror to see his face clearly for shaving. Eye exams like the Snellen chart test visual acuity, helping diagnose and correct vision defects with lenses typically ranging from 1.0 to 3.5 D for reading glasses.
Step-by-step explanation:
To determine how close a nearsighted man must stand to a mirror to see himself clearly when shaving, we must understand how mirrors affect vision. For a person who is nearsighted and has a clear vision limit of 20 cm, when looking into a mirror, the light reflecting off the mirror is effectively doubling the distance the light travels. This means that objects that are actually 20 cm behind the mirror will appear just at the clear vision limit of the nearsighted person. Therefore, for the man to see his face clearly in the mirror while shaving, he should stand 10 cm away from the mirror so that the reflected image is within 20 cm from his eyes.
Various eye exam tests, such as the Snellen chart, are used to evaluate visual acuity and can help determine if someone requires glasses or contacts. These exams are essential for identifying changes in vision that may affect one's ability to see near or distant objects, indications of presbyopia, or other eye health issues.
The power of an eye's lens changes with age, and therefore, different diopter lenses may be prescribed by an optometrist to correct vision defects. These corrective lenses can range from 1.0 to 3.5 D for reading glasses, while stronger prescriptions may be given for more severe nearsightedness or farsightedness.