Question

What difference is seen in the intensity (brightness) of the image of the flame on the screen?

Answer 1

Hint : The image which can be obtained on a screen is known as a Real Image. For a real object, a real image is formed only by a concave mirror or by a convex lens. The real images formed by the concave mirror or the convex lens are inverted and magnified.

Complete solution:
In physics, Intensity is defined as the amount of energy falling per unit normal area per unit time.
Intensity of light is the measure of the wave-length weighted power emitted by a light-source in a particular direction per unit solid angle. Based on the luminosity function, a standardized model of the sensitivity. SI unit of luminous (cd) candela.
Formula:
The intensity is defined as power per unit area, and power is defined as energy per unit time,
$I = PA = E\Delta E1A$
When the flame is moved towards the convex lens the magnification goes an increasing i.e. image size goes on. Increasing image size goes on increasing because of which most of the light-energy get distributed over larger areas reducing the intensity of light.
Hence the intensity of light goes on decreasing, every time the flame moves towards the lines.

Note:
The quantity of visible light that emitted in unit time per solid angles. The unit for quantity of light flowing from a source is any one second.
Intensity of light decreases with every time the flame moves toward the lens.