Which of the following is the best as shaving mirror?

Analyze the question: A shaving mirror must give a magnified, upright image of the face when the face is close to the mirror.

Explain the concept:

• Concave mirror: When an object is placed between the pole (P) and the principal focus (F), the image is virtual, upright, and magnified. This is the key property for shaving.
• Convex mirror: Always gives a virtual, upright but diminished image. It is used as a driving or security mirror for a wide field of view, not for magnification.
• Plane mirror: Gives an upright image of the same size. There is no magnification, so fine details are not enlarged.
• Parabolic mirror: Used for car headlamps, torches, and searchlights (a point source at the focus gives a parallel beam), and for telescopes. It is not used for shaving.

Solution:

1. When shaving, the face is held close to the mirror, closer than the focal length.
2. A concave mirror then produces an enlarged, erect, virtual image, so you can see small hairs and skin detail clearly.
3. A convex mirror shrinks the image, a plane mirror does not enlarge it, and a parabolic mirror is meant for beam production.

Answer: The best shaving mirror is the concave mirror, so the answer is A.

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Exam tip: Remember the uses of mirrors:

• Concave → "Cave in to shave" (shaving and makeup mirrors, dentist's mirror)
• Convex → "Vex the view" (wide view, such as driving mirrors)
• Parabolic → headlamps and searchlights