It covers the topics --measuring focal length,mirror formula,magnification,rules for tracing images by convex mirror,image formation by convex mirror,uses of convex and concave mirrors.

1. LEARNING OBJECTIVES --- VIDEO 4
•MEASURING FOCAL LENGTH OF A CONCAVE MIRROR.
•MIRROR FORMULA
•LINEAR MAGNIFICATION PRODUCED BY MIRRORS.
•RULES FOR TRACING IMAGES FORMED BY CONVEX MIRRORS.
•IMAGE FORMATION BY CONVEX MIRRORS.
•CHARACTERISTICS OF IMAGES FORMED BY CONVEX MIRRORS
•USES OF SPHERICAL MIRRORS.
•DIFFERENCE BETWEEN IMAGE FORMED BY PLANE, CONCAVE
AND CONVEX MIRRORS

2. MEASURING FOCAL LENGTH OF A CONCAVE MIRROR
• When an object is at infinity , its image is formed at the focus of concave
mirror.
• Take a metre rod and hold it horizontally with its zero end resting against a
wall.
• Hold the concave mirror vertically on the meter scale and move the mirror
on the scale till a clear image of a distinct object like tree is formed on the
wall.
• Read the position of concave mirror on the metre scale .This gives us
approximate focal length of concave mirror.

3. MIRROR FORMULA
• Mirror formula is a relation between object distance (u), image distance (v)
and focal length (f) of a spherical mirror.
• It can be written as—
• u= distance of the object from the pole of the mirror.
• v= distance of the image from the pole of the mirror.
• f= distance of principal focus of the mirror from the pole.
• If R is radius of curvature of the spherical mirror, then f=R/2.

4. LINEAR MAGNIFICATION PRODUCED BY CONCAVE MIRROR
• Linear magnification by concave mirror is defined as the ratio of height of
the image (h2) to the height of the object (h1).
• It is represented by m.
• m=height of image /height of object
• Or m=h2/h1
• Case 1: When image is magnified or enlarged, size of image is greater than
the size of the object i.e.h2>h1.
• m=h2/h1 therefore m>1
• Case 2: When image is of the same size as that of the object, h2=h1
• m=h2/h1, m=1.
• Case 3: When the image is smaller than the object, h2<h1
• m=h2/h1, m<1

5. MAGNIFICATION
• The image formed may be real or virtual, depending on the position of the
object. Therefore two cases arise:
• 1.When the image is real and inverted i.e .the image lies below the
principal axis. Therefore h2 is negative .As height of the object is always
positive, so m=h2/h1=negative
• This means when m is negative ,image formed is real and inverted.
• 2.When the image is virtual and erect i.e the image lies above the principal
axis. Therefore h2 is positive. As height of the object is always positive ,so
m=h2/h1=positive.
• This means when m is positive, image formed is virtual and erect.
• Magnification of spherical mirror is also related to object distance(u) and
image distance (v). So m can be represented as
• m=h2/h1 =-v/u

6. RULES FOR TRACING IMAGES FORMED BY CONVEX MIRROR
• RULE 1: A ray of light falling on the mirror in a direction parallel to the
principal axis of a convex mirror, appears to be coming from its focus ,on
reflection from the mirror.

7. RULES FOR TRACING IMAGES FORMED BY CONVEX MIRROR
• RULE 2: A ray of light falling on a convex mirror on passing through
centre of curvature of the mirror is reflected back along the same path i.e
such a ray retraces its path on reflection .

8. RULES FOR TRACING IMAGES FORMED BY CONVEX MIRROR
• RULE 3: A ray of light falling on a convex mirror on passing through focus
of the mirror, becomes parallel to the principal axis of the mirror, on
reflection .

9. RULES FOR TRACING IMAGES FORMED BY CONVEX MIRROR
• RULE 4: A ray of light incident obliquely towards the pole P of a convex
mirror is reflected obliquely such that the incident and reflected rays make
equal angles with the principal axis.

10. IMAGE FORMATION BY CONVEX MIRROR
• CASE 1: When the object is at infinity.
• Image formed is—
• Virtual and erect.
• Behind the mirror , at F.
• Highly diminished.

11. IMAGE FORMATION BY CONVEX MIRROR
• CASE 2: When the object is at finite distance from the mirror.
• Image formed is—
• Virtual and erect.
• Between pole P and focus F.
• Diminished in size .

12. CHARACTERISTICS OF IMAGES FORMED BY CONVEX MIRROR
Positions and Nature of Image in Convex Mirror
Position of Object Position of Image Size of Image Nature of Image
At infinity
At F, behind
mirror
Highly diminished Virtual and erect
Between infinity
and P
Between F and P,
behind mirror
Diminished Virtual and erect

13. USES OF SPHERICAL MIRRORS

14. USES OF SPHERICAL MIRRORS

16. SUMMARY
• MEASURING FOCAL LENGTH OF A CONCAVE MIRROR.
• MIRROR FORMULA
• LINEAR MAGNIFICATION PRODUCED BY MIRRORS.
• RULES FOR TRACING IMAGES FORMED BY CONVEX MIRRORS.
• IMAGE FORMATION BY CONVEX MIRRORS.
• CHARACTERISTICS OF IMAGES FORMED BY CONVEX MIRRORS
• USES OF SPHERICAL MIRRORS.
• DIFFERENCE BETWEEN IMAGE FORMED BY PLANE, CONCAVE
AND CONVEX MIRRORS