Question

Diagram shows a rectangular coil ABCD, suspended freely between the concave pole pieces of a permanent horse shoe magnet, such that the plane of coil is parallel to magnetic field.

(i) State your observation, when current is switched on. 

(ii) Give an explanation for your observation in (i). 

(iii) State the rule, which will help you to find the motion of rotation of coil. 

(iv) In which position will the coil ultimately come to rest? 

(v) State four ways of increasing the magnitude of force acting on the coil. 

Answer 1

(i) The coil ABCD will turn. The arm AB of the coil will move out of the plane of paper and arm CD into the plane of paper. Thus, coil will turn in anticlockwise direction. 

(ii) A magnetic field is set up by the coil due to the passage of electric current. The magnetic field of the coil is at right angles to the magnetic field of permanent magnet. Thus, a magnetic couple acts, which turns the coil. 

(iii) Fleming’s left rule: It states : Stretch the thumb, the forefinger and the middle finger of left hand, such that forefinger points in the direction of magnetic field; middle finger points in the direction of current. Then, the thumb points in the direction of motion of conductor. 

(iv) The coil will come to rest at right angles to the direction of magnetic field. 

(v) (a) By increasing the number of turns in coil. 

(b) By increasing the area of cross-section of coil. 

(c) By placing laminated soft iron core within the coil. 

(d) By increasing the magnitude of current coil.