Light — Important Questions

Rule 3: Ray passing through the focus

Step 1: There are four rules for constructing ray diagrams for spherical mirrors. Step 2: Rule 1 states a ray through C reflects back along the same path. Step 3: Rule 2 states a ray parallel to the principal axis passes through (or appears to come from) the focus after reflection. Step 4: Rule 3 is the reverse of Rule 2 — a ray through the focus reflects parallel to the principal axis. Step 5: Rule 4 deals with a ray hitting the pole, where angle of incidence equals angle of reflection. So the correct answer is Rule 3.

It provides a wider field of view and always forms an erect image

Step 1: A convex mirror always forms a virtual, erect, and diminished image regardless of the object's position. Step 2: Because the reflecting surface curves outward, it captures light from a larger area, giving a wider field of view compared to a plane mirror. Step 3: The erect image helps the driver correctly identify the orientation of vehicles behind. Step 4: The diminished image means vehicles appear smaller (and farther) — this is why mirrors carry the warning 'Objects in the mirror are closer than they appear.' Step 5: Option A is wrong because convex mirrors form diminished (not magni

Focal length of a convex mirror is positive

Step 1: In the Cartesian sign convention, the pole P is the origin, and the principal axis is the x-axis. Step 2: The object is always placed on the LEFT side of the mirror (incident light comes from the left). Step 3: Distances measured in the direction of incident light (towards the mirror, i.e., left to right) are positive. Distances measured opposite to incident light are negative. Step 4: For a convex mirror, the focus is BEHIND the mirror (on the right side), which is in the direction of incident light, so f is POSITIVE. Step 5: For a concave mirror, focus is in front (left side), so f i

The image is real, inverted, and twice the size of the object

Step 1: The formula for magnification is m = –v/u = height of image/height of object. Step 2: The magnitude of m is 2, which means the image is TWICE the size of the object (magnified). Step 3: The NEGATIVE sign of magnification (m = –2) indicates the image is REAL and INVERTED. Step 4: A positive value of m would indicate a virtual and erect image. Step 5: So m = –2 means: real image, inverted, magnified 2 times. Option A is wrong (negative m = real, not virtual). Option C is wrong (magnitude = 2, not 0.5). Option D is wrong (erect images have positive m).