Astigmatism: cornea curvature not spherical, different focal lengths in different planes. Corrected by cylindrical lens which has different powers in perpendicular axes. Not simple spherical lens.
Explanation:
Ammeter measures current, must be in series so full current flows through it. Low internal resistance to minimize voltage drop. Voltmeter measures potential difference, connected in parallel, high resistance.
Explanation:
Convex mirror gives wider field of view, always forms virtual, erect, diminished image. Allows driver to see larger area. Concave can magnify but field narrow. Plane gives normal view but limited field.
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