Question

a student focuses the image of a candle flame placed about about 2 metres from a convex lens of focal length 10 cm on a screen after that he most gradually the flame towards the lens and each time focus is its image on the screen . after that he moves gradually the flame towards the lens and each time focuses its image on the screen a.In which direction does he moved the lens to focus the flame on the screen b.What happens to the size of the image of the flame formed on the screen c.What difference is seen in the intensity brightness of the image of the screen d.What is seen on the screen when the flame is very close at about 5cm to the lens
pls answer with full explanation no cheating​

Answer 1

Position of the object is more than 2f. The ray is considered as a parallel ray. So real, pointed size ,inverted and more intense image is formed at f. If object distance(u) decrease, image distance(v) increase and size of the object increase, it is real and inverted, intensity decreases. When u=f  real image is formed at infinity. If u is less than f virtual erect enlarged image is formed in the same direction of the object.

Answer 2

(a) The student moves the lens away from the screen to focus the image because on moving the candle towards the lens, the image distance increases.

(b)The size of the image increases when the object is moved towards the lens.

(c) Intensity of the image decreases.

(d) When the candle is moved very close to the lens, no image is formed on the screen. A virtual image is formed behind the candle on the same side of the screen.