Magnetic field around a current

Introduction to electromagnetism

Have you noticed how a generator works or why NEPA light makes a small buzz near big transformers? It is because electricity and magnetism are like twins. In 1820, a scientist named Oersted found out that whenever current flows through a wire, it creates a magnetic field around that wire.

Simply put, any wire carrying current becomes a temporary magnet while the light is on.

Magnetic field around a straight wire

Imagine you are holding a straight wire standing upright. When current flows up, the magnetic field lines form concentric circles around the wire. These circles are closer together near the wire because the force is stronger there.

To find the direction of these circles, we use the Right-Hand Grip Rule. Imagine gripping the wire with your right hand so your thumb points in the direction of the current. Your four fingers will curl in the direction of the magnetic field.

Magnetic field in a circular coil

If you bend that straight wire into a loop or a circle, the magnetic field lines pass through the center of the loop. At the very center, the field lines are almost straight and very strong because the effects from all sides of the loop add up together.

Magnetic field in a solenoid

A solenoid is just a long coil of wire wrapped many times like a spring. When current flows, it behaves exactly like a bar magnet. One end becomes the North pole and the other becomes the South pole.

It is like a 'tubular magnet' that you can turn on and off with a switch.

Factors affecting field strength

You can make the magnetic field stronger by doing three things:

1. Increasing the amount of current flowing through the wire.

2. Increasing the number of turns in the coil or solenoid.

3. Inserting a soft iron core inside the coil to help gather the magnetic lines.

Sample calculation of field strength

For a long straight wire, the magnetic flux density B is calculated using the formula: B = (mu₀ * I) / (2π r), where mu₀ is 4 * pi * 10^-7 T m A^-1.

Example: Calculate the magnetic flux density at a point 0.05 m away from a wire carrying 10 A of current.

Step 1: Write down values. I = 10 A, r = 0.05 m. Step 2: Use the formula B = (4 * pi * 10^-7 * 10) / (2π 0.05). Step 3: Cancel pi and solve. B = (2 * 10^-6) / 0.05 = 4 * 10^-5 T.