Que-Ans Magnetic Effect of Electric Current

1.Describe an activity to show that the magnetic field lines produced when current is passed through the circular coil.
Answer.
Aim : To study the characteristics of magnetic field produced by a current carrying circular coil at its centre.
Apparatus Required : Rectangular cardboard having two holes, Thick copper circular coils of different radii having known number of turns, key, battery, rheostat, stand, iron filings.
Procedure :

Pass the coil through the two holes of cardboard in such a way that half of the loop is above the cardboard and remaining part should be below it and normal to the plane of cardboard.
Connect the circuit as shown.

• 

Sprinkle iron filings uniformly on the cardboard.
 Allow the current to pass though the coil by inserting plug in the key.
Note the pattern of iron filings that emerges on the cardboard after tapping gently a few times.
Place the compass at any point over the pattern of field. Observe the direction of needle.

Observations :
(a) Iron filings are arranged in the form of concentric circles.
(b) The concentric circles become larger and larger as we move away from the wire.

(c) At the centre of loop, lines are almost straight and perpendicular to the plane of the loop.
Conclusion :

• The concentric circles at every point of a current carrying circular loop represent the magnetic field around it.
• Magnetic field line close to the axis of loop is straight and is perpendicular to the plane of the coil.
• Field lines keep on diverging as we move away from the centre of loop.

2. What is meant by solenoid? How does a current carrying solenoid behave? Give its main use.
Answer. Solenoid: A coil of many circular turns of insulated copper wire wound on a cylindrical insulating body (i.e., cardboard etc.) such that its length is greater than its diameter is called solenoid.
When current is flowing through the solenoid, the magnetic field line pattern resembles exactly with those of a bar magnet with the fixed polarity,
i.e. North and South pole at its ends and it acquires the directive and attractive properties similar to bar magnet. Hence, the current carrying solenoid behave as a bar magnet.
Use of current carrying solenoid: It is used to form a temporary magnet called electromagnet as well as permanent magnet.

3. With the help of a diagram of experimental setup describe an activity to show that the force acting on a current carrying conductor placed in a magnetic field increases with increase in field strength.
Answer.
Aim : To show that force acting on a current carrying conductor placed in a magnetic field increases with the field strength.
Apparatus Required : Aluminium rod, stand horse shoe magnet of different intensity, cell, key and connecting wires.
Procedure :

1. .Arrange the set-up as shown in figure.
   2.Plug the key, the current flowing through the rod from Q to P observe the displacement of rod.
   3.Now unplug the key and remove the first horse shoe magnet and place the second horse shoe magnet of higher magnetic field strength in a similar manner to that of first.
   4.Plug the key, the current again flow through the rod from Q to P. Again observe the deflection of rod.
   5.Now bring both’the magnet closer together (to ensure greater magnetic field than that of previous case). Again observe the motion of rod.

Observations : Each time, the conductor moves faster than that of previous one. It is possible only when conductor gets accelerated more each time which required more force. (F = ma)
Thus, if the magnetic field strength is increased, the rod will experience a greater force and move faster.
Conclusion : The force acting on a current carrying conductor placed in a magnetic field increases with increase in field strength.