JEE Main 2024 · 5 April · evening · Single correct · +4 / −1
The vehicles carrying inflammable fluids usually have metallic chains touching the ground:
- (a) To protect tyres from catching dirt from ground
- (b) It is a custom
- (c) To alert other vehicles
- (d) To conduct excess charge due to air friction to ground and prevent sparking
Answer and solution
Answer (d) To conduct excess charge due to air friction to ground and prevent sparking
Solution
Physics sir · 4 steps
A moving tanker rubs against air and picks up charge; the chain gives that charge a safe road to the ground.
- Charge builds up. As the vehicle moves, its body rubs against the air and gets charged by friction. The rubber tyres are insulators, so this charge has no way to leak to the ground and keeps piling up on the metal body.
- Why that is dangerous. Enough charge creates a strong electric field near the body. When that field breaks down the air, a spark jumps across, and a spark near inflammable fluid or its vapour can start a fire.
- What the chain does. A metal chain touching the road is a conductor connecting the body to the earth. The excess charge flows away continuously through it, so the charge never grows large enough to cause a spark.
- So. The chain is there to conduct the charge from air friction to the ground and prevent sparking, which is option (d).
The idea to keep. Whenever something insulated moves and rubs, think charge build-up. Earthing with a conductor drains that charge before it can spark, which is why fuel trucks and aircraft refuelling hoses are grounded.
Answer from the NTA final answer key. Solution by PrepWiser.