The diagram below shows a magnetic needle kept just below the conductor AB which is kept in North South direction.
(i) In which direction will the needle deflect when the key is closed?
(ii) Why is the deflection produced?
(iii) What will be the change in the deflection if the magnetic needle is taken just above the conductor AB?
(iv) Name one device which works on this principle.
Answers
According to Right Hand Thumb Rule for magnetic field, when we hold a current carrying conductor in right hand , where the thumb points towards the direction of current. When we wrap the fingers around the conductor, the fingers points towards the direction of the magnetic field lines .
i) In first case when a magnetic needle is kept just below the conductor , when the key is closed the current is from B to A . So, applying Right Hand Thumb Rule just below the conductor , the direction of magnetic field is towards East . So, needle will deflect towards East .
ii) The deflection is produced due to magnetic field when current is passed through the wire .
iii) In second case when a magnetic needle is kept just above the conductor , when the key is closed the current is from B to A . So, applying Right Hand Thumb Rule just above the conductor , the direction of magnetic field is towards West . So, needle will deflect towards West .
iv) Device which works on this principle is magnetic sensor .
(i) Needle Deflects Towards The West.
(ii)On passing current in the wire AB, a magnetic field is produced around it and the magnetic Needle experiences a torque in the magnetic field, so it Deflects to align itself in the direction of magnetic field at that point.
(iii) Needle Will Deflects Towards The West.
(iv) Electric Motor.