Live wire, neutral & ground (earth wire) - Domestic circuits (part 1) | Physics | Khan Academy

Summary

This video explains the science behind electrical plugs, focusing on the three wires inside them: live, neutral, and ground. It explores how the live wire carries high voltage, while the neutral wire is close to the ground's voltage, and the ground wire ensures safety by directing excess current safely into the earth. The video also highlights the importance of the third ground pin in preventing electric shocks, explaining how its longer and thicker design ensures safety by connecting the ground first and disconnecting last. The video concludes with practical advice about why some plugs don't require a ground pin and emphasizes the safety of properly handling electrical devices.

Takeaways

• 😀 The top pin of a plug is usually longer and thicker than the other two pins to ensure safety during use.
• 😀 The two main wires in a plug are the live (red) wire and the neutral (black) wire, each serving different functions.
• 😀 The live wire has a high voltage, and the voltage alternates between positive and negative, while the neutral wire remains at a low or zero voltage.
• 😀 The difference in voltage between the live and neutral wires in India is typically around 220V.
• 😀 The live wire is called 'hot' or 'live' because it can give a dangerous shock due to its fluctuating high voltage.
• 😀 The neutral wire is safer to touch because it remains close to ground voltage, but still poses a risk due to potential faults.
• 😀 The ground or earth wire (green) is used for safety, directing stray electrical current into the ground rather than through a person.
• 😀 The ground wire is crucial for high-power devices to ensure that any electrical fault doesn't cause harm by diverting current to the ground.
• 😀 The ground pin is longer than the other two pins to ensure that it connects first when the plug is inserted and last when it is removed.
• 😀 The ground wire helps prevent electric shocks in faulty situations by providing a low-resistance path for the current, directing it safely into the earth.
• 😀 Not all devices require a ground pin; low-power devices like mobile chargers may only need two pins because the risk of shock is minimal.

Q & A

Why is the top pin of a plug usually longer and thicker than the other two pins?

The top pin is the ground pin, and its longer and thicker design ensures that it connects first when plugging in. This design makes sure that the safety ground connection is established before the device is powered on, preventing potential electric shocks.

What is the difference between the live and neutral wires in an electrical plug?

The live wire (often red) carries high voltage that alternates between positive and negative. The neutral wire (often black) maintains a voltage close to ground (zero), ensuring the safe return of the electric current.

Why do we call the live wire 'hot'?

The live wire is called 'hot' because it carries a high voltage that alternates between positive and negative, creating a potentially dangerous situation if touched. It’s the wire with the higher voltage in comparison to the ground.

Why are there two wires (live and neutral) in an electrical circuit if the current alternates direction?

Although current alternates direction, the live wire carries the alternating voltage, while the neutral wire is at or near ground potential. The current alternates between these two wires, allowing for efficient energy transmission and usage.

Why doesn’t the neutral wire cause a shock when touched, compared to the live wire?

The neutral wire's voltage is close to zero, the same as the ground. As a result, there is no significant voltage difference between the neutral wire and the ground, so no current flows through the body when touching it.

What happens if a fault occurs and the live wire touches the metallic body of an appliance?

If the live wire touches the metallic body of an appliance and the body is not properly grounded, it can cause a dangerous electric shock if someone touches the appliance. The electricity would flow through the person to the ground, leading to a severe shock.

How does the ground wire prevent electric shocks?

The ground wire (green in color) provides a safe path for electric current to flow directly into the ground in case of a fault. By offering a lower resistance path than the human body, it ensures that electric current flows through the wire instead of through someone touching the appliance.

Why don’t all devices, like mobile chargers, have a third (ground) pin?

Devices like mobile chargers use very low current, so the risk of a dangerous shock is minimal. In these cases, a third pin (ground) is unnecessary since the electric current is so small that any potential shock wouldn't be harmful.

What is the purpose of the green ground wire in a three-pin plug?

The green ground wire is designed to provide safety by directing any leaking current from a fault away from the person and into the ground. This ensures that electrical shocks are avoided, even in cases where the live wire may come into contact with the metallic parts of an appliance.

Why is it important for the ground pin to be thicker than the other two pins?

The ground pin is thicker to ensure proper orientation of the plug, preventing it from being inserted into the wrong socket. Its thickness also ensures a reliable connection to the ground, providing safety by ensuring the ground connection is established before the live and neutral connections.