3.adding more coils to the wire
4.placing a metal bar within the coils
Magnetic field:
Magnetic fields occur whenever charge is in motion. As more charge is put in more motion, the strength of a magnetic field increases.
Lets take all the given options one by one:
1. On straightening the wire, it will generate magnetic field.
- A long straight wire carrying a current is the simplest example of a moving charge that generates a magnetic field.
2. On changing the direction of current flow the direction of field gets reversed thus the strength of magnetic field will change.
3. On adding more coils to the wire the strength of magnetic field will increase.
- The strength of an electromagnet can be increased by increasing the number of loops of wire around the iron core.
4. On placing a metal bar within the coils the magnetic field is greatly increased.
5.The magnetic field disappears when the current is turned off thus losing its magnetic field strength.
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