Problem and solution
A 2 cm high object is placed on the principal axis of a
concave mirror at a distance of 12 cm from the pole. If the image is inverted,
real and 5 cm in height, find the location of the image and the focal length of
the mirror?
We can solve this problem basing on the very definition of
magnification and the mirror formula. Magnification is defined as the ratio of
height of the image to the height of the object. The other way of defining the
magnification is as the ratio of distance of the image to the distance of the
object. The sign of the magnification is negative which means that object and
image are in the different directions. The problem is solved as shown below.
An object is placed in the principal axis of a concave mirror
at a distance X from a principal focus.
The images formed at a distance Y the focus. What is the focal length of the
mirror ?
This problem also has to be solved basing on the mirror
formula. Being both object and the major place to before the mirror they shall
be treated as negative and a concave mirror focal length is also negative.The solution is shown in the above diagram.
Problem and solution
An object is placed in front of a concave mirror at a distance
of 50 cm. A plain mirror is introduced covering the lower half of a convex
mirror. The distance between the object and the plain mirror is 30 cm. It is
found that there is no gap between the image formed by the two mirror. Then
what is the radius of curvature of the convex mirror?
In the problem object is placed at a distance of 50 cm from a
concave mirror. Between the object and the mirror at a distance 30 cm from the
object a plain mirror is placed. That means the plain mirror is a distance of
20 cm from the convex mirror. The image of the object due to the plain mirror
will be farmed again at the 30 cm as a virtual image in the backward direction
as shown. And hence it is going to be 10 cm behind the convex mirror.
The same shall be the image of the convex mirror also as it
is given in the problem that both the images are coinciding with each other.
Therefore we know that the object is in front of the mirror
at a distance of 50 cm and the image is behind the concave mirror at a distance
of 10 cm and using the mirror formula we can calculate the focal as shown
below.
Problem and solution
Two blocks each of mass m lies on a smooth table. They are
attracted to the two other masses as shown. The pullies are straight and light.
An object to is kept on the table as shown. The surfaces of the two blocks are
made are reflecting surfaces. Find the acceleration of the two images by the
two reflecting surfaces with respect to each other?
We shall try equations of motion using Newton’s laws. We
shall draw free body diagram and
identify the direction of motion. The forces along the direction of motion
shall be treated as positive and vice versa. As shown in the below diagram, we can
write the equations of motion and derive acceleration of the individual images.
As per the law of optics, the acceleration of the image is
twice the acceleration of the mirror.
As the two images are moving in the opposite direction, we
can calculate the relative acceleration is the sum of the two accelerations.
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