Design a burglar alarm You decide to build your own burglar...

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?

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?

Key Concepts

Practicality in Sensor and Alarm Design

When designing circuits or sensors that rely on induced currents from minimal sources like Earth's magnetic field, issues such as low signal strength, noise, and sensitivity become significant. This concept involves understanding the engineering and physical limitations that can affect the performance of devices intended to trigger alarms or perform other functions based on subtle electromagnetic changes.

Electromagnetic Induction

Electromagnetic induction is the process of generating an electric current in a conductor by changing the magnetic field it is exposed to. This principle is at the heart of many electrical devices, including generators and transformers, and is generally governed by the laws of electromagnetism.

Faraday's Law

Faraday’s Law quantifies electromagnetic induction by stating that the electromotive force in a circuit is proportional to the rate of change of the magnetic flux through the circuit. It serves as a fundamental principle for understanding how motion in a magnetic field can create voltage in a conductor.

The Magnitude of Earth's Magnetic Field

The Earth's magnetic field, although critical in navigation and natural phenomena, is extremely weak compared to magnetic fields generated by industrial magnets. Its low intensity means that the induced voltages from movement in this field are typically minimal, posing challenges for practical energy harvesting or detection applications.

Transcript

00:03 There are a few things to consider over here.

00:07 First of all, if this is our, this is the earth, then the magnetic field goes something like that and that.

00:38 So this is running from, this is the north pole and this is the south pole.

00:47 Inside the earth you can consider that there is a magnet where the south pole is over here and the north pole is over here and all the magnetic field lines run like that now if we assume that there is a building over here which is north facing the window will look like this and at that point from inside the room it will look like the magnetic field is pointing outwards and the magnetic field of the earth is 8 times 10 to the negative 5 tesla for simplicity let us just assume that the doors and the window is one meter by one meter in dimension which means the flux passing through the window is b -a which is 8 times 10 to the negative 5 tesla meter square now if you think that this so in this diagram north 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 projection of the area along the magnetic field goes to zero so this is the flux 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 north -south now the total flux is zero let us assume that you open the window in one second so in that particular case the change in flux over change in time magnitude of that will give us the induced electric field which will come out to be 8 times 10 to the minus 5 volt.

03:48 You can easily use a step -up transformer to bump up the voltage to, let's say, 110 -volt as in the us.

04:04 So for that, you will need a factor of, an amplification factor of about 10 to the 6...

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