 Today, we are going to discuss automobile wiper and speedometer. I am Mr. Nageshar Tambaki, assistant professor, Department of Mechanical Engineering, Vahachan Institute of Technology, Solaapur. Learning outcome. At the end of this session, students will be able to explain electric horn and speedometer. So in this particular session, we are going to discuss two things that is windshield wiper and the speedometer. First of all, we will see what is the importance of the windshield wiper. So windshield wiper is a device, okay, you think about it. So we will discuss what is the importance of the windshield wiper. So here it is, windshield wiper is a device that cleans water, snow or mud from the windshield of the vehicle and it is a small device of our car and which will give you a driving and overall safety. They can remove rain, snow, okay, the pollen frost and other debris quickly and smoothly at push-off button. So next thing is that this is the circuit diagram of windshield wiper. Here the different parts of the windshield wipers are shown, so which will cleanse the water, snow or mud from the windshield of the vehicle. Thus it ensures proper visibility of the road ahead. This system finds application on a large variety of locomotives from vehicles, railways to airplanes. Generally the term windscreen wiper refers to the wipers installed on the front windshield of a vehicle. However, nowadays rear wipers are also getting popular. Almost all the modern wipers mechanism employ an electric motor for their operation. So however, in some cases pneumatic drivers are also used to drive wiper arms. Some of the primitive designs of the wiper mechanism were hand operated. And rain sensing wipers is a recent development in the wipers. So what is done in this particular wiper? So in this wiper there is a limiting switch, there is a battery and there is a wiper switch. When you turn on the wiper switch that time the current sends from battery towards the motor of the wiper then motor starts rotating and due to which what will happen a windscreen wiper starts oscillating. So that mechanism is provided over here. So limiting switch is a limiting the wiper angle and due to that what will happen the certain portion of the glass will be cleaned. And rain sensing, rain sensor unit is there over here. So in this particular rain sensor unit whenever the rain starts falling on the vehicle that time it senses that particular rain and automatically it starts oscillating, the wiper starts oscillating and it cleans the glass of the vehicle. So for which we require the windscreen wiper. So the next thing is that, that is the speedometer. So speedometer, here is what we want out of our speedometer. We have the cars wheels rotating at a certain speed and we want to know with a simple pointer and dial what that speed is. So we need to connect the spinning wheels to the pointer in some clever fashion. Even that is pretty tricky, the wheels are racing around but the pointer some distance away merely flicks back and forth how do we convert continuous spinning motion into intermittent flickery pointer motion. The answer is to the electromagnetism. The shaft that turns the car wheels is connected to the speedometer by a long flexible cable made of twisted wires. The cable is a bit like a mini driveshaft if one end of the cable rotates so does the other even though the cable is long and bendy. At the top end the cable feeds into the back of the speedometer. When it rotates it turns the magnet inside the speedometer case at the same speed. The magnet rotates inside a hollow metal cup known as the speed cup which is also free to rotate through restraint by a fine coil of wires known as hairspring that is shown in this particular figure. However the magnet and the speed cup are not connected together they are separated by air. The speed cup is attached to the pointer that moves up and down the speedometer dial. How does it all work? As the speedometer cable rotates it turns the magnet at the same speed. The spinning magnet creates a fluctuating magnetic field inside the speed cup and by the laws of electromagnetism that means the electric current flows inside the cup as well. In effect the speed cup turns into a kind of electricity generator. Unlike in a proper generator the kind that makes electricity for your home in a power plant. The current in the speed cup has nowhere to go there is nothing to carry their power away so the currents just swim about uselessly in the swirling eddies we call them as eddy currents. For that very reason since the electric currents and there are moving in an electric conductor inside a magnetic field another law of electromagnetics says that they will create motion. How? The currents actually makes the speed cup rotate in such a way that it tries to catch up with the spinning magnet. But the hairspring stops the cup from rotating very fast so it just turns a little bit instead. Pulling the pointer up and the dial as it does so. The faster the car goes the faster the cable turns. The quicker the magnet spins the bigger the eddy current it generates. The greater the force on the speed cup and the more it is able to pull the pointer up the dial. If you can picture all that clearly take a look at this particular animation. So when the engine turns over the driveshaft turns to make the wheel spin around. The speedometer cable powered by the driveshaft turns as well. The cable spins the magnet around at the same speed inside the speed cup. The magnet rotates continuously in the same direction that is in the case counter clockwise. The spinning magnet creates eddy currents in the speed cup. The eddy currents make the speed cup rotate counter clockwise as well in an attempt to catch up with the magnet. For that the magnet and the speed cup are not joined together in any way there is air in between them. So likewise this particular speedometer is going to work and which will give us the actual reading of the vehicle at walk speed it is running in kilometer per hour. So this particular device is a very important device in our vehicle and whenever a driver look at it then he comes to know that at what speed our vehicle is running and he also realizes at what particular road surface how much speed is required. So this is the perfect indicator to know the driver to balance his vehicle. So likewise this particular speedometer is working. So these are the references please refer thank you, thank you.