Magnetic Effects of Electric Current
This chapter covers how electric current produces a magnetic field, the working of electromagnets and electric motors, and electromagnetic induction used in generators.
A magnetic field is the region around a magnet or current-carrying conductor in which its magnetic influence can be felt. It is represented by field lines that emerge from the north pole and merge at the south pole.
If a current-carrying conductor is held in the right hand such that the thumb points in the direction of current flow, the curled fingers show the direction of the magnetic field lines circling the conductor.
Q. What is the difference between an electromagnet and a permanent magnet?
An electromagnet is a temporary magnet created by passing electric current through a coil wound around a soft iron core, and it loses its magnetism when the current is switched off. A permanent magnet retains its magnetism without any external current.
Fleming's left-hand rule gives the direction of force on a current-carrying conductor in a magnetic field: if the first finger points in the direction of the field, the second finger in the direction of current, the thumb gives the direction of the force (motion).
Q. State the principle on which an electric generator works.
An electric generator works on the principle of electromagnetic induction: when a coil is rotated in a magnetic field, the magnetic flux through the coil changes, which induces an electromotive force (and hence a current) in the coil.
Which rule is used to find the direction of force on a current-carrying conductor placed in a magnetic field?
Correct answer: (B) Fleming's left-hand rule
A device used to protect electrical circuits from short-circuiting or overloading is called a _______.
Fuse
The magnetic field inside a long straight solenoid carrying current is non-uniform.
False — the magnetic field inside a long current-carrying solenoid is fairly uniform, which is why a solenoid can behave like a bar magnet with one end acting as a north pole and the other as a south pole.