A student obtained a sharp image of a frills of a window using a concave mirror. His teacher remarked that for getting better results a well lit distant object ( preferably the sun ) should be focussed on the screen. What should be done for this purpose? a) Move the screen slightly away from the mirror b) Move the screen and the mirror away from the object c) Move the screen and the mirror towards the object d) Move the mirror slightly towards the screen The answer is " d) Move the mirror slightly towards the screen " Why is it so??