Magnetic field due to a current in a solenoid , Force on a current-carrying conductor in a magnetic field, Fleming’s left hand rule, electromagnet

 

Magnetic field due to a current in a solenoid

 

Solenoid:--

Solenoid is a coil of many circular turns of insulated copper wire which are wrapped closely in the shape of a cylinder is called a solenoid.

Magnetic field lines of the magnetic field near current carrying solenoid.

 

 

 

A solenoid having current is used to magnetise the rod inside it

 

 

 

The magnetic field around the current carrying solenoid is similar to the magnetic field around the bar magnet.

One end of the solenoid behaves as (or act as) magnetic north pole

Other end of the solenoid behaves as (or act as)  the magnetic south pole.

In the solenoid  , The magnetic field  lines are In the form of the parallel straight lines.  This shows that magnetic field is same at every points insides  the  solenoid. That is , the magnetic field is uniform inside the solenoid.

A electromagnet consists of a core of soft iron wrapped with a coil of insulated copper wire

When s current is flowing through a solenoid , a strong magnetic field is produced inside a solenoid which can be used to magnetise a piece  of magnetic material (like soft iron ) when placed inside the coil . the magnet so formed is called as electromagnet.

 

 

Force on a current-carrying conductor in a magnetic field

 

An electric current is flowing through a conductor produces a magnetic field. The produced magnetic field exerts a force on a magnet placed near to the conductor.

A rod AB having current exerts a force which is perpendicular to its length and magnetic field.

 

To demonstrate the force due to a magnetic field acting on the current carrying conductor   ,  assume a small  aluminium  rod  is connected with two connecting wires and its suspended freely horizontally from a stand.

Now take a strong horse shoe magnet. And place the strong horse shoe magnet in such a manner that the rod is kept between the two poles with the magnetic field directed upwards.

For this, the north pole of the magnet is put vertically below the aluminium rod . And south pole of the magnet is put vertically above the aluminium rod.

Now to make the circuit connections, connect the aluminium rod In series with a battery , a key and a rheostat.

Now , the electric current is passed through the aluminium rod from end B to end A.

After that we observed that the rod gets displaced. The rod is now displaced towards the left.

Now , if we reverse the direction of the current flowing through rod and we get the direction of the rod move toward the right direction.

By doing this , we observes  the displacement of the rod explain that  the current carrying aluminium rod is placed in a magnetic field , a force is being exerted.

It also suggests that when the direction of the current   passing through  the conductor is reversed  , then the direction of the force is also reversed.

Now, if we change the direction of the magnetic field to vertically downwards by interchanging both two poles of the magnet. Then we observed that the direction of the force acting on the current carrying rod gets reversed.

This show that direction of the force on the conductor is depends on the direction of the current and direction of the magnetic field.

 

Also , we observed that the when the magnitude of the force is more , when the direction of the current is at right angles to the direction of the magnetic fields.

 

 

 

 

Fleming’s left hand rule:--

 

Consider that the direction of the current and that of the magnetic field is perpendicular to each other and found the force is also perpendicular to both of them.

These three directions can be explained by the simple rule. that rule is called as fleming’s left hand rule.

According to the fleming’s left hand rule, stretch the thumb , forefinger and middle finger of your left hand in a such a manner that they are mutually perpendicular to each other. If the first finger is pointing in the direction of the magnetic field and second finger is pointing in the direction of the current , then the thumb will points in the direction of the motion or the force acting on the conductor.

 

 

 

 

 

 

 

This rule is used to find the direction of the force on the conductor.