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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I vote for jmartis's solution. The statement that one of the bulbs would "never really light" is wrong, as far as I can see. If the resistor is very small, the volt drop across it will be small, and the bulb shunted by the resistor will not light at all, while the other one lights almost fully. Pressing the button will force the full supply voltage across the resistor, and thus across the bulb shunting it. A huge current will flow and lots of power will be wasted, but nobody said it had to be efficient.
You may be able to achieve the same thing by using two dissimilar bulbs in series, a high wattage one and a low wattage one. A light bulb has a much lower resistance when cold. So the high wattage bulb will stay out and the small one will light brightly. Then pressing a switch shunted across the low wattage bulb will extinguish it and light the big bulb. In this case there would be nothing in the box except the switch and some wires
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Just some hints:
1. Both bulbs have same resistance (ON) 2. Solution requires only 3-4 resistors 3. Using 4 resistors, there is a solution that allows both bulbs to be illuminated identical with same voltage across them when they are turned on.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I actually dont understand anything any more... what is really wrong in jmartis's and my solution, ? Obivously only one battery must be used, and voltage on blb has to be zero when off, right? Jmartis seemed winner, whas wrong with his schematic?
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
by that (ON) next the the bulbs resistance are you implying that we are supposed to use the change in resistance of the light bulb as it heats up as a part of the circuit?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Firkragg wrote ...
I actually dont understand anything any more... what is really wrong in jmartis's and my solution, ? Obivously only one battery must be used, and voltage on blb has to be zero when off, right? Jmartis seemed winner, whas wrong with his schematic?
Going to sleep now im babbling already..
Well, Jmartis used two supplies for one. Supposed to be single source.
Registered Member #79
Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673
How's about this?
When you push the button, voltage is no longer dropped across L1 and you can adjust R2 to whatever you want to modify it's brightness. You could also add a resistor above R1 if you care about the volt drop being the same.
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Electrical Quizzes - QUIZ 8 POSTED
