Request a call back

Join NOW to get access to exclusive study material for best results

CBSE Class 10 Answered

A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.
Asked by polyrelation | 19 Mar, 2019, 08:27: PM
answered-by-expert Expert Answer
Height of the needle (h1) = 4.5 cm
Object distance( u) = – 12 cm
Focal length of the convex mirror (f)= 15 cm
Image distance = v
The value of v can be obtained using the mirror formula:
1/f = 1/v - 1/u
1/u = 1/v - 1/f
= 1/-25 - 1/5
= -5 -1/25
= -6/25
u = -25/6 = -4.167 cm
1/v = 1/f - 1/u
1/f = 1/u + 1/v
= 1/15 + 1/12
= 4 +5/60
= 9/60
f = 60/9 = 6.7 cm
Hence, the image of the needle is 6.7 cm away from the mirror. Also, it is on the other side of the mirror.
The image size is
m = h2/h1 = -v/u
h2 = -v x h1 /u
= -6.7 x 4.5/ -12 = 2.5 cm
Hence Hence, magnification of the image, m = h2/h1 = 2.5/4.5 = 0.56
The height of the image is 2.5 cm. The positive sign indicates that the image is erect, virtual, and diminished.
If the needle is moved farther from the mirror, the image will also move away from the mirror, and the size of the image will reduce
Answered by Ankit K | 19 Mar, 2019, 11:08: PM

Concept Videos

CBSE 10 - Physics
Asked by Trisha Gupta | 14 Nov, 2021, 01:14: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 10 - Physics
Asked by masterprathamesh421 | 02 Jul, 2021, 06:27: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 10 - Physics
Asked by purnimap035 | 27 May, 2021, 07:56: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 10 - Physics
Asked by bhavikabhatia1125 | 27 May, 2021, 06:53: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
Get Latest Study Material for Academic year 24-25 Click here
×