A student sees cracked plug with exposed copper.Explain danger and correct action

Short answer: The exposed copper is a live conductor you can touch — the danger is a fatal electric shock and, if the bare wires touch each other, sparking, overheating and fire. Do not touch the plug. Switch off the supply at the socket switch or the main breaker, warn others, and have a qualified person replace the plug or the whole lead.

Why it is dangerous

1. Shock / electrocution. A crack in the casing means the live (brown) wire is within reach. Mains is \(230\ \text{V}\), and a dry hand is only about \(1000\ \Omega\): \[ I = \frac{U}{R} = \frac{230}{1000} \approx 0{,}23\ \text{A} \] That is about \(230\ \text{mA}\), while roughly \(30\ \text{mA}\) through the chest can already stop the heart. Wet hands lower \(R\) further and make it far worse.
2. Fire. Cracks let moisture and dust in, so current can creep across the surface (tracking) and arc. If the bare live and neutral wires touch, you get a short circuit: a large current, a hot spot, melted plastic and flames.
3. Protection may not save you. The fuse and earth wire protect the apparatus, not a person touching bare copper. A broken casing also means the cable clamp no longer grips, so pulling the lead exposes even more copper.

Correct action, in order

1. Don't touch it — not the plug body, not the copper, and don't try to push it in or pull it out.
2. Switch off at the wall if the switch is safe to reach, or better, switch off the circuit breaker.
3. Keep others away and keep it away from water; put it out of use with a warning note.
4. Report it to the teacher or lab technician. Only a qualified person should fit a new plug or replace the lead.
5. Never wrap it in insulating tape or use it again — a taped crack is still a cracked plug.

If someone is already being shocked: don't grab them. Switch off the supply first, then call for help.

Check your answer: a full mark answer names both risks (shock and fire), says don't touch it, says isolate at the mains, and says report it so it is replaced, not repaired with tape.