A point object is placed on the principal axis at 60 cm infront of a concave mirror of focal length 40 cm on the
principal axis.If the object is moved with a velocity of 10 cm/s (a) along the principal axis, find the velocity of
image (b) perpendicular to the principal axis, find the velocity of image at that moment.
Answers
Answer: HERE THE ANSWER IS HPOE IT HELPS MARK ME IN BRIAN PLZ I BEG
Explanation:
A point object is placed 60 cm from the pole of a concave mirror of focal length 10 cm on the principal axis.(a) u=-60cm
f=-10cm
v=
fu
u-f
=
-10(-60)
-60-(-10)
=-12cm
(b)
1
v
+
1
u
=
1
f
differentiating, we get dv=-
v2
u2
du=-(
-12
-60
)2[1mm]=-
1
25
mm
[∵du=1mm sign of du is + becuase it is shifted in +ve direction defined by sign convention.]
(A) -ve sign of dv indicates that the image will shift towards negative direction.
(B) The sign of v is negative. Which implies the image is formed on negative side of poie (A) and (B) together imply that the image will shift away from pole.
Note that diffentials dv and du denote small changes only.
(h) Newton's formula XY=f2
X and Y are the distances (along the principle axis) of the object the image respectively form the principle focus. This formula can be used when the distances are mentioned or asked form the focus.
