Car-ல இந்த கோடு Accident நடக்காம தடுக்குதா?
4 Minutes
Learn how car defoggers work using heating wires to clear misty windows and prevent accidents in this Tamil science lesson for students.
- Testing nichrome wire and a battery to clear fogged glass
- Joule heating in appliances like iron boxes and water heaters
- How rear defogger lines and front vents clear windshield mist
What this lesson teaches
The horizontal lines seen on the rear window of a car are electrical heating elements that make up a defogger, which clears mist and condensation from the glass. By warming the glass and evaporating moisture, the defogger gives the driver an unobstructed view of vehicles behind and helps prevent accidents.
How Joule heating works
When an electric current passes through a conductive material that resists the flow of electricity, electrical energy converts into thermal energy and heats the material. This resistance to current is called electrical resistance, and the resulting temperature rise is known as Joule heating. Common household appliances such as electric iron boxes and water heaters use this heating principle to function.
Testing mist removal with nichrome
- A cold piece of glass taken from a refrigerator becomes covered in foggy condensation.
- Wires made of nichrome, a combination of nickel and chromium, are stretched across the foggy glass.
- Nichrome has high electrical resistance, meaning it strongly resists the flow of electric current.
- Connecting the nichrome wires to a battery causes them to heat up and rapidly evaporate the moisture.
Rear window defoggers in cars
Instead of nichrome, rear car windows use heating lines made from materials such as silver and ceramic. These conductive lines are applied as surface coatings or embedded directly into the rear glass during manufacturing. When the driver presses the defogger button, electric current from the car battery flows through the lines, heating the glass and clearing mist so traffic behind remains visible in the rear-view mirror.
Defogging the front windshield
Front car windshields generally do not feature visible heating lines like the rear glass. Instead, the front glass is cleared of mist using the vehicle air conditioning system. The driver increases the air conditioning temperature and presses the front defogger button, which blows hot air through special vents located at the base of the dashboard to evaporate the moisture on the windshield.