Question

A needle is placed 10 cm from a plane mirror. The mirror is then moved 5cm
farther away from the needle. What is the final distance between the needle
and its image?
C.
20cm


A.10cm
D.25cm
B. 15cm
E. 30cm​

Answer 1

Answer:

30 cm will be answer .

Explanation:

IN CASE OF PLANE MIRROR THE DISTANCE OF IMAGE FROM MIRROR IS SAME AS DISTANCE OF OBJECT FROM MIRROR SO DISTANCE BETWEEN OBJECT AND IMAGE IS TWICE THAT OF DISTANCE BETWEEN OBJECT AND MIRROR .IN THIS QUESTION THE FINAL DISTANCE BETWEEN NEEDLE AND MIRROR IS 15 cm so final distance between needle and its image is 30 cm.

Answer 2

Answer:

It is to be remembered that a convex mirror always forms the virtual, erect and diminished image.

Given: Object distance, u=−10cm     Focal length, f=15cm

To find: Image distance, v

From mirror formula :

v

1

​

+  

u

1

​

=  

f

1

​

 

v

1

​

−  

10

1

​

=  

15

1

​

 

v

1

​

=  

15

1

​

+  

10

1

​

=  

150

25

​

 

v=6cm

Hence image will be formed 6 cm beyond the mirror, i.e virtual magnification

m=  

u

−v

​

=  

−10

−6

​

=0.6

Hence it will be erect and diminished.

Explanation: