Question

Two coils of insulated copper wire are wound over a non -conducting cylinder as shown. Coil I has larger number of turns. 

(i) Write your observations when, 

(a) key K is closed, 

(b) key K is opened.

(ii) When the current is passed continuously through coil I. Give reason for your observations. 

(iii) Name and state the phenomenon responsible for the above observation. 

(iv) Write the name of the rule that is used to determine the direction of current produced in the phenomenon. 

(v) Name the two coils used in this experiment.

Answer 1

(i) (a) A momentary deflection is shown by the galvanometer.  

(b) A momentary deflection is shown by the galvanometer but in the opposite direction. 

(ii) When key is closed or opened, the current in the coil I change, therefore the magnetic field linked with coil II  changes and hence a current is induced in it. 

(iii) The electromagnetic induction: The process by which a changing magnetic field in a conductor induces a current in another conductor.

(iv) Fleming's Right-Hand Rule: Stretch the first three fingers of the right hand mutually perpendicular to each other such that the forefinger gives the direction of magnetic field and the thumb points in the direction of the motion of a conductor then, the middle finger will give the direction of the induced current

(v) Primary coil - coil I

Secondary coil - coil II  

Answer 2

(i) (a) When key is closed, the galvanometer needle deflects momentarily in one direction.  

Reason: When key is closed, magnetic field lines around coil 2 increases momentarily. This causes an induced current to flow through it and hence deflection occurs in one direction. 

(b) When key is opened, the galvanometer needle deflects again momentarily but in opposite direction. Reason: When key is open, magnetic field lines around coil 2 decreases momentarily. This causes an induced current to flow in opposite direction. Hence, deflection occurs in opposite direction. 

(ii) When current is passed continuously through coil I, no deflection is observed in the galvanometer. 

Reason: There will be no change in magnetic field lines passing through the coil 2. Hence, no induced current will be set up in coil 2. 

(iii) The phenomenon observed in above cases is electromagnetic induction. It is a process by which a changing magnetic field in a conductor induces a current in another conductor placed nearby. 

(iv) Fleming’s right hand rule 

(v) Coil I – Primary coil Coil II – Secondary coil