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### You want to build a generator for a multi-day can…

00:10
Indian Institute of Technology Kharagpur
Problem 57

# Design a burglar alarm You decide to build your own burglar alarm. Your window frames are wood, so you decide to fit the sides with metal sliders and the bottom with metal strips. These changes will turn the window area into a metal loop whose size changes as the window opens. Your idea is that an electric current will be induced in this loop as the window opens in Earth’s magnetic field. The current can set off an alarm if a burglar enters. How feasible is your idea?

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## Video Transcript

There are a few things to consider over here forced to fall. If this is our this is the art, then the magnetic field goes something like that and that So this is running from this is the North Pole and this is the South Pole. Inside the art, you can consider that there is a magnet where the South Pole is over here on the north. Bodies over here and all the magnetic field designs run like that. Now, if we assume that there's a building over here which is not facing which is not facing, the window will look like this. And at that point from inside the room, it would look like the magnetic field is pointing outwards and the magnetic field off the art is eight times 10 to the negative five. Yes, that for simplicity that has just as human that the door seven though the window is one meter by one meter in dimension, which means the flocks passing through the window ease be a which is eight time Stand to the navy. Five Jessica Mr Sweat. Now, if you I think that this so in this diagram Ah, not is out of the plane. This is the north direction. This is east, and that's west. When you swing the window by 90 degree, when you swing the window by 90 degree, then the window points along the magnetic field, so the production off the area along the magnetic field goes to zero. So they seize the fox that we have found when the window is lying east west and when the window is swings out by 90 degree. So it goes by, not south. Now that rasac zero, let us assume that you open the window in one second. So in that particle, their guests, the change in flocks over changing time magnitude off that with Give us the induced electric field, which was come out to be eight times 10 to the minus five you want you can easily use Ah, step up transformer to bump up the voltage, too. That's 100 10 volts, as in the US, So for that you will need a factor off an amplification factor off about Tendered. A six 10 to the six will get you do 80 world, so that's like 1.5 times 10 to the sixth. Let's say, however, over here I have designed the system such that these are window that looks not. You can have other situations where the window is not look not but it was look somewhere in the middle. So if I do our top of you now, not so eastern West, it might be like Ah, window is opening from this direction to that direction and in this case, the induced electric field will be difficult to ascertain. It was off course across the zero, so that can be perceived. However, I have chosen that the window is opened within one second, which may not be OK, especially if ah burglar is happening. They will be careful to open the window much slower and that will result in much smother induced, filled the density with increase. If you open its lord and then the induced electric field will decrease in that case, so it will be difficult to find exactly how much voltage is being generated. However, this can definitely be passed through our rectifier circuit and brought up to a detectable limit to trigger an alarm. So what you need is, uh, exact location has been you exact location and on house geometry like is it not facing the south facing in the Eastern Western artist? Not with that has to be figured out. Exact location and direction has to be accounted. Sword In orderto bring the garden up to our detective limit. You have to use step up transformer and rectification circuit.