Saturday, 9 September 2017

Class 10 - Physics - Light and Reflection - Magnification Chart For Mirrors (#cbseNotes)

Light and Reflection -
Magnification Chart For Mirrors

Class 10 - Physics - Light and Reflection - Magnification Chart For Mirrors (#cbseNotes)


Q: What is Magnification?

Answer: The ratio of height of image to the height of an object is known as magnification of an image and is denoted as m.

           Image height         h'     -v
    m = -------------------- = ---- = ----
           Object height        h       u
 


The +ve value of magnification represents virtual image of an object.

The -ve value of magnification represents real image of an object.


Q: Using magnification formula, prove that image formed by a plane mirror is at the same distance as object but behind the mirror. It is given that in plane mirror, object height and image height are equal.




Answer: In plane mirror h' = h

     h'        -v
m = --- = 1 =  ---
     h          u

⇒ v = -u


∴ image formed by a plane mirror is at the same distance as object but behind the mirror.



Magnification and Type of Image and Mirror


Magnification(m) Type of image and its size Type of Mirror
+1 Virtual erect and of same size as an object Plane
-1 Real inverted and of same size as an object. Concave
>1 and -ve Real inverted and magnified Concave
< 1 and -ve Real inverted and diminished Concave
> 1 and positive Virtual, erect and magnified Concave
< and positive Virtual, erect and diminished Convex





Q: The magnification of a mirror is -2. Height of the object is 15cm. What is the height of the image? What type of image will it be?

Answer: Given m = -2, h = 15cm, h' = ?
h' = m ✕ h = -2 ✕ 15cm = -30cm

It forms real inverted and enlarged image.