Oersted experimentally found that current carrying conductor apply force on magnet. He observed the deflection of magnetic needle placed vicinity of current carrying conductor, so he conclude
- Electric current is a source of magnetic field.
- Magnetic field due to current carrying conductor apply force on magnet.
We extend this concept and think opposite to that.
Does magnetic field apply force on conductor? Marie Ampere, a famous physicist worked on this and found answer of this question.
So we understand this with the help of an experiment.
Consider a conducting rod AB. Adjust it such that it can freely move on the plane of paper. Connect voltage supply and allowed to flow current through it by key k. Put magnet on upper side of page facing north pole towards the page. Place another magnet backside of page such that south pole facing towards the page. The magnetic filed due to this magnet is crossing the page and going inward as shown in figure.
Tap key to on. Current will flow in rod from terminal A to terminal B. When current flow in rod , the rod tends to move towards west. Why do this move towards west?
If current carrying conductor apply a force on magnet then according to Newton’s third law, magnetic field also apply equal amount of force on conductor. Due to this, the conducting rod moves toward west. The direction of force applied on conducting wire by magnetic field is find using Fleming’s left hand rule.
Fleming’s left hand rule: Current carrying conductor, magnetic field and force lies in three different directions so it is quite complicated for understanding. To understand this Fleming gives a simple rule to find force on current carrying conductor due to magnetic field.
Make arrangement of fingers of left hand perpendicular to each other as shown in figure.
Fleming left-hand rule states function of each finger as
Middle finger: The middle finger gives the direction of flow of charge means current.
First finger: The first finger gives the direction of magnetic field.
Thumb: Thumb gives the direction of force.
So directions of magnetic field, current and force are perpendicular to each other.
Applications:
The discovery of relationship between magnetic field and electric current gives birth to modern technology. DC motor, electric generator, loudspeaker, microphone, ammeters, voltmeters and other measuring devices are the result of this.
Q) An electron moves upward and enters in a region of magnetic field which lies from South to North. Does magnetic field exertforce on that electron? If yes then state the direction of applied force?
Q) An electron moves from South to North and enters in a region of magnetic field which lies from South to North. Is magnetic field exerts force on that electron? If yes then state the direction of applied force. Is answer same if direction of field will reverse?
Answers the following questions:
- T parallel conducting wires flow a current in same direction towards North. Will they apply a force on each other?If yes then state direction.
- Electron and alpha particles moves parallel to each other towardswest. Atwhich direction alpha particles apply force on electron?
- State the direction of force. The direction of magnetic is perpendicular to page going inward and electron moves North as showing in figure.