Video: Understanding the Wires of a Plug

Which of the following statements correctly explains the purpose of the live wire in a standard UK plug? [A] The live wire is for safety; it prevents the casing of the device from becoming live; it only carries a current when there is a fault. [B] The live wire completes the circuit of the device; the potential difference between the live wire and Earth is 0 V. [C] The live wire provides the alternating potential difference that powers the device.

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Video Transcript

Which of the following statements correctly explains the purpose of the live wire in a standard UK plug? 1) The live wire is for safety. It prevents the casing of the device from becoming live. It only carries a current when there is a fault. 2) The live wire completes the circuit of the device. The potential difference between the live wire and Earth is zero volts. 3) The live wire provides the alternating potential difference that powers the device.

Okay, so in this question, we’ve been asked to find a statement that correctly explains the purpose of the live wire in a standard UK plug. Now the first statement says that the live wire is for safety. It says that the live wire prevents the casing of the device from becoming live. And it only carries a current when there is a fault.

Now this most certainly is not what the live wire does. In fact, this is the purpose of the Earth wire. The Earth wire is present in a standard UK plug in order to carry current away from the plug and the device when something goes wrong. It carries all of this current into the Earth. Hence, it’s known as the Earth wire.

This way, if something goes wrong within the plug or the device and a human being touches that device, they’re not gonna get shocked. So anyway, this statement describes the Earth wire and hence is not the answer to our question.

So let’s look at number two. This statement says that the live wire completes the circuit of the device and that the potential difference between the live wire and Earth is zero volts. Now this also does not describe the live wire. This in fact describes the neutral wire. It is the neutral wire that completes the circuit. And the potential difference between the neutral wire and the Earth is zero volts.

Therefore, it’s the potential difference between the live wire and the neutral wire that powers the device. But since the neutral wire is at zero volts and we know that, in the UK, the electricity operates at 230 volts, the live wire is, therefore, at 230 volts relative to the Earth. And so this statement is not the answer to our question either because it describes the neutral wire.

So, finally, number three. The live wire provides the alternating potential difference that powers the device. So yes, this is why a live wire is called a live wire, because it provides the potential difference, the alternating potential difference. And this is what powers the device. Hence, statement three is the correct definition of the purpose of the live wire. The live wire provides the alternating potential difference that powers the device.

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