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 2007-09-14, 15:13 #1 mfgoode Bronze Medalist     Jan 2004 Mumbai,India 80416 Posts Projected Pictures. When a screen is placed 10 feet from a projector, the picture occupies 10 sq.ft. How large will the picture be when the projector is 15 feet from the screen? Mally
 2007-09-14, 15:32 #2 Wacky     Jun 2003 The Texas Hill Country 32×112 Posts How about "10 sq ft" because that is the size of the screen. or There will be no picture at all because the power cord isn't long enough to reach the mains.
 2007-09-14, 15:45 #3 victor     Oct 2005 Fribourg, Switzerlan 25210 Posts 15ft :)
 2007-09-14, 17:16 #4 Mr. P-1     Jun 2003 7·167 Posts 22.5 sq. feet.
2007-09-14, 23:12   #5
Orgasmic Troll
Cranksta Rap Ayatollah

Jul 2003

641 Posts

Quote:
 Originally Posted by Mr. P-1 22.5 sq. feet.
ditto

 2007-09-15, 04:09 #6 retina Undefined     "The unspeakable one" Jun 2006 My evil lair 10111011100112 Posts 2.0903184 m^2
2007-09-15, 07:22   #7
mfgoode
Bronze Medalist

Jan 2004
Mumbai,India

22×33×19 Posts
Tricky solutions.

Quote:
 Originally Posted by victor 15ft :)

Well Victor, the others were right including Wacky with his lateral thinking.

Retina gave a tricky conversion from sq. ft to sq. metres.

Mr. P-1 and OT were on the dot too.

To be honest I was bowled over too !

You see, you cannot compare linear feet with square feet.

One has to square the linear feet into square feet.

Thus 10^2 = 100 sq.ft.

15^2 =225 sq.ft.

Then set up the proportion

10 : 100 = x : 225

Thus x = 22.5 sq.ft.

Hence the picture will have an area of 22.5 sq.ft. when the projector is 15 ft
from the screen.

Mally

2007-09-15, 07:57   #8
retina
Undefined

"The unspeakable one"
Jun 2006
My evil lair

177316 Posts

Quote:
 Originally Posted by mfgoode To be honest I was bowled over too !
I am amazed how this simple algebra would bowl you over and yet you say you managed to solve Beals conjecture! &

 2007-09-15, 08:18 #9 davieddy     "Lucan" Dec 2006 England 2×3×13×83 Posts Note that "10 sq.ft." <> "10 ft square"
 2007-09-15, 08:33 #10 davieddy     "Lucan" Dec 2006 England 194A16 Posts Optics Treat the projector as a simple convex lens, and take the distance of the screen to be measured from the optical centre of this lens. If we assume the images are accurately focussed, then we find that the object slide/film is closer to the lens for an image distance of 15 feet. So the angle subtended is larger in the second case giving a larger image than you have all been assuming. David Last fiddled with by davieddy on 2007-09-15 at 08:38
2007-09-15, 10:40   #11
victor

Oct 2005
Fribourg, Switzerlan

22·32·7 Posts

Quote:
 Originally Posted by davieddy Note that "10 sq.ft." <> "10 ft square"
Haha, now I see why my answer was incorrect!

I thought the image was fitting a 10 ft square screen :)

Thank you David!

If 10ft away from the beamer the image occupies 10ft x 10ft, 15ft away the image is 15ft x 15ft big.

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