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.
Magnets are everywhere. They can be permanent magnets or electromagnets. Magnets come in many shapes and sizes but they also come in different strengths.
It depends on what is meant by strength. Two common measures of a magnet’s strength are the strength of the magnetic field and pull force.
The magnetic field strength is expressed in Gauss or Tesla (1 Tesla = 10,000 Gauss). It depends on the size, shape, grade of the magnet and where the measurement is performed.
We will use a magnetometer sensor available in this smartphone to measure the strength of the magnetic field. Science Journal App is used to visualize data captured by the sensor.
As We move the bar magnet near the sensor, the strength of the magnetic field goes up. It comes back to original value as I move the bar magnet away. Same is true for other pole as well.
Electromagnet also behaves in a similar manner. We can see the proportional increase in strength with increase in current.
What if you don't have a magnetometer ? You can design your own scale with everyday things and compare the strength of the magnetic field quantitatively.
I will take this small steel ball and place it at a distance. I will slowly move the magnet towards the ball. The point at which ball is attracted towards the magnet is noted. We can note it down and compare the strength of all the magnets we have. Off-course this is our local scale.
Another way is to place a magnet in the bowl filled with balls and measure how many are attracted. By calculating the average, you can arrive at some number.
We can also compare strength based on the weight magnet can lift as well.
Let us attach this magnet to the wooden base here and calculate pull force. This nut with a container is stuck to the magnet. We will put balls in this container till it pulls the magnet down. This will be one measure of the strength of the magnet.
Same can be tried with a Neodymium magnet as well. It seems we need more force to pull the nut down. Let us tie this bottle and increase the force by adding water. It took 700 ml of water or approximately 7 Newtons.
You can try these variations to calculate the strength of the magnetic field.
