Q   (a) A lamp is arranged in a boxbehind a circular hole with a thin vertical wire: the light fromthe hole falls on a converging lens and a plane mirror placed 10.0cm behind the lens as indicated in the diagram. The box andvertical wire are then moved until an image of the vertical wireappears in sharp focus on a piece of paper placed alongside thevertical wire. The distance between the wire and lens is thenmeasured and found to be 20.0 cm. What characteristic property ofthe lens does this length represent?

Suggest how it would bepossible to show that this image of the vertical wire isinverted

(b) The vertical wire isremoved and a metal plate with a small hole at its centre placedacross the hole in the box. On the diagram above, draw two raysemerging from the hole and show their paths as they pass throughthe lens and subsequently.

(c) The plane mirror isreplaced by a white screen. What would be observed on thisscreen?

(d) The metal plate isnow removed and the vertical wire replaced. The positions of lensand screen, of size equal to that of the object.

What would be thedistance?

(i)between the vertical wire and the lens,

(ii)between the lens and the screen?

(e) The screen isremoved and the lens is moved until it is only 10 cm from thevertical wire. Explain how it would be possible with the lens inthis position for you to see a clear image of the verticalwire.

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