Question: Explain the right hand thumb rule and cork and screw rule to find the magnetic field due to a current carrying conductor.
Answer: Imaging a current carrying conductor held in your right hand such that the thumb points in the direction of current, then the curl of your fingers encircling the conductor will give the direction of magnetic field lines around the conductor.
Maxwell’s cork screw rule (Right hand screw rule): imagine a right handed screw to be rotated in the direction of current screw to be rotated in the direction of current, then the direction of current, then the direction of rotation gives the direction of magnetic field lines.
Question: What are magnetic field lines? How is the direction of magnetic field at a point determined? Mention two important properties of magnetic field lines.
Answer: A magnetic field line is:
- A pictorial representation of the magnetic field around a magnet.
- A path straight or curved, the tangent to which at any point gives the direction of the magnetic field at that point.
- A path which will be followed by a “hypothetical” north pole in the magnetic field of another magnet id it is allowed to move freely.
The direction of magnetic field is found by using the right hand palm rule.
Magnetic field lies possess the following properties:
- They travel from the North to the South Pole of a magnet outside the magnet and from South to the North Pole inside the magnet.
- They are continuous closed curves.
Question: What is the nature of magnetic field produced by a straight current carrying conductor? Explain the help of an experiment.
Answer: The magnetic field produced around a straight current carrying conductor is in the form of concentric circles with center lying on the straight conductor.
Take a copper wire AB. Pass it through a cardboard. Connect the wire to a battery through a key. Sprinkle some iron fillings on the cardboard gently. You will find that the iron filings arrange themselves in the form of concentric circles. Reverse the direction of current by changing the polarity of the battery. You will find that this time too, the iron filings arrange themselves in concentric circle but in opposite direction.
Hence, the magnetic field lines of force around a straight conductor carrying electric current are concentric circles with the conductor at the center. The direction of magnetic field changes the direction of current is reversed.