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2007-09-14, 15:13
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#1 |
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Bronze Medalist
Jan 2004
Mumbai,India
22·33·19 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 
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2007-09-14, 15:32
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#2 |
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. 
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2007-09-14, 15:45
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#3 |
Oct 2005
Fribourg, Switzerlan
22×32×7 Posts |
15ft :)
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2007-09-14, 17:16
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#4 |
Jun 2003
7×167 Posts |
22.5 sq. feet.
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2007-09-14, 23:12
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#5 | |
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Cranksta Rap Ayatollah
Jul 2003
641 Posts |
Quote:
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2007-09-15, 04:09
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#6 |
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Undefined
"The unspeakable one"
Jun 2006
My evil lair
2×3×1,013 Posts |
2.0903184 m^2
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2007-09-15, 07:22
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#7 | |
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Bronze Medalist
Jan 2004
Mumbai,India
80416 Posts |
Tricky solutions.
Quote:
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
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2007-09-15, 07:57
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#8 | |
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Undefined
"The unspeakable one"
Jun 2006
My evil lair
2·3·1,013 Posts |
Quote:
 & 
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2007-09-15, 08:18
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#9 |
"Lucan"
Dec 2006
England
2×3×13×83 Posts |
Note that "10 sq.ft." <> "10 ft square"
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2007-09-15, 08:33
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#10 |
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"Lucan"
Dec 2006
England
2×3×13×83 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 |
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2007-09-15, 10:40
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#11 | |
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Oct 2005
Fribourg, Switzerlan
22·32·7 Posts |
Quote:
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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