Solenoid

 

Solenoid

This is a straight wire, carrying current. We have seen the nature of the magnetic field generated around it.

The magnetic field due to straight wire is distributed along its length.

Strength of this field can be increased at a specific point if  we place many small wires like this or  form a loop by joining these two ends. 

Magnetic field formed due to a loop is very small and can be enhanced by having more such loops next to each other.  This can be achieved by closely winding wire into helical shape like this around a pipe.  We can wrap this wire with cellotape. Pipe is used to support the coil.

 In the study of electromagnetism, a solenoid is a coil whose length is substantially greater than its diameter. 

If I place the needle compass outside the solenoid, nothing happens. Same compass if placed near one end of the solenoid, and the needle is deflected.

The magnetic field is formed inside the coil. Let us find out more about it. 

We will place this needle compass such that part of the needle is inside the coil. When the current flows through the coil, the North pole of the needle is pulled inside. This end is behaving like the South Pole of the coil as we know that opposite poles attract.. Let us switch direction of current and find out if it is the same case. This time the needle is pushed away.  This end is now behaving like a North Pole as we know that similar poles repel. 

Let us perform the same activity with another needle compass on the right side of the coil ? 

Left and right side of the coil are behaving like a regular  magnet. It has the North Pole and South Pole. Type of the pole is decided by the direction of current. 

We can say that solenoid behaves like a regular magnet. The type of the pole is decided by the direction of current flowing through the coil.

How about the magnetic field inside the coil ? Let us form a rectangular pipe with this plastic sheet. We will wind this coated copper wire with 100 turns . When the needle compass is placed at various locations inside the coil, the needle aligns itself along the vertical axis of the coil. The direction of this alignment is decided by the direction, current is flowing through the coil. 

However, Solenoid is the generic term for a coil of wire used as an electromagnet. Electromagnets with fixed cores are not considered solenoids.

Solenoid refers to any device that converts electrical energy to mechanical energy using a solenoid which has a moving core. The device creates a magnetic field from electric current and uses the magnetic field to create linear motion. Common applications of solenoids are to power a switch, like the starter in an automobile, or a valve, such as in a sprinkler system.

These railway signals are all controlled by solenoids.

You can also build solenoid with coated copper wire wound around a pipe or you can use paper straw or pen for the same.

We can also build this solenoid with coated copper wire and more turns. It makes a magnetic field inside more powerful.

Let us pour iron filings into this solenoid. When current is passed, a magnetic field is created inside. This can be seen by the orientation of iron filings.

You can place it on the ring magnet and watch it jump .This will happen only when poles repel each other.

Do try this at home.

Thank you.