EasyPhysicsHigh School (9–10)Electricity & Magnetism › Magnetic Effects of CurrentConceptualBoard Exam
A coil without a core gives a field of 2.4 mT inside…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A coil without a core gives a field of inside. A soft iron core makes the field times as strong.
- What is the field with the core, in tesla?
- Why is soft iron used, and not steel?
- Give two other ways to make the electromagnet stronger.
Need a reminder? The key ideaShow
Inside a long solenoid the field is strong and uniform: , where is the number of turns in each metre and . A soft iron core makes it an electromagnet, many times stronger, that loses its magnetism when the current stops.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) .
Step 2. (b) Soft iron becomes a strong magnet while the current flows and loses its magnetism at once when it stops. Steel would stay magnetised, so the electromagnet could not be switched off.
Step 3. (c) Use a larger current, or more turns in each metre.
Answer: ; soft iron loses its magnetism when the current stops; a larger current or more turns.
Check. A scrapyard crane must drop its load, which is why its core is soft iron.
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