Calculate Image Diameter of Sun in Concave Mirror with Given θ and f

[vkash]

θ

Homework Statement

The sun of (diameter D) subtends an angle of θ radians at the pole of the concave mirror of focal length f. The diameter of the image of the sun formed by mirror is _____

Homework Equations

1/v+1/u=1/f

The Attempt at a Solution

confused with question. Either i am getting zero or infinity(sun is too large!)..

 

[technician]

The sun can be taken to be at infinity so the image of the sun will be formed... where?
Light rays striking the centre of the mirror (from the top/bottom of the sun) will be reflected at same angle.
Can you get it from this?

 

[vkash]

The sun can be taken to be at infinity so the image of the sun will be formed... where?
Light rays striking the centre of the mirror (from the top/bottom of the sun) will be reflected at same angle.
Can you get it from this?

when light strike at the pole of the concave mirror they are reflected like plane mirror. So No image should form?
Am i correct?

 

[PeterO]

when light strike at the pole of the concave mirror they are reflected like plane mirror. So No image should form?
Am i correct?

No, only one ray from each point on the sun strikes the pole of the mirror. All the other rays strike somewhere else.
You do know what direction one other special ray will reflect, and every other ray from a given point on the sun will reflect through that same point - forming an image of that point.
Choosing a point on the "top" of the sun, and another on the "bottom"of the sun will enable you to locate the extent of the image of the sun.

 

[PeterO]

when light strike at the pole of the concave mirror they are reflected like plane mirror. So No image should form?
Am i correct?

btw - have you ever seen an image of the sun "reflected in the side of a sky scraper"?
That should answer your question about whether an image is formed after reflection in a plane mirror.