Question

What happens to the size of the image of the flame formed on the screen?

Answer 1

Understand the lens formula and apply the equation for the given case study question. Find out how the initial conditions are given for a convex lens and hence derive at your conclusion. For the size of the image, get to know about the magnification formula.

Complete Step By Step Solution:
In order to understand this question, we first analyze the lens formula,
Lens formula is given a,
$\dfrac{1}{v} = \dfrac{1}{f} + \dfrac{1}{u}$
Where, $v$ is the final image distance, $u$ is the distance of the source from the lens and f is the focal length of the given lens.
Now, when the lens is moved towards the source, we obtain a clear image on the screen, which at a distance $v$ from the lens. The image is said to be real and inverted.
To find out whether the size of the image remains same or magnified, we use the magnification formula, which is given as
$m = \dfrac{v}{u}$, where $m$ is magnification, $v$ is image distance and $u$ is source distance.
Now, when the lens is moved towards the object, $u$ decreases and $v$ increases. Since, the values are in ratio, it is clearly seen that magnification increases as distance of source from lens decreases.
Thus the image formed will be magnified and larger than the original source.
The image gets magnified, is the right answer for the given question.

Note:
Magnification produced by the concave lens is always less than 1, since the image is formed on the same side of the source object and the nature of the image is virtual and upright.