NUSH PC3131_ Electromagnetism

Electromagnetism Ethan Chew M24304 Contents of this notes package: Chapter 11 PC3131, Electromagnetism Chapter 12 PC3131, Electromagnetic Induction Bridging the Gap Electricity and magnetism are not two separate phenomena. Let’s explore how these two fundamental properties of nature interact with each other! Recall your abbreviations: I - current, B - magnetic field. Before we can visualise their interactions, we must first establish a way to express vectors in 3D space on our 2D paper. The following shows the notations of current / magnetic field vectors pointing in the third dimension: Now, consider the case where a current is flowing through a straight wire out of the page, like so:

The core concept of Electromagnetism is that a moving charge generates a magnetic field. The grey lines surrounding the current (going out of the page) is the magnetic field generated by said current. The magnetic field strength gets weaker the further we move from the wire (indicated by the increasing space between the concentric circles). Now, you may realise I’ve indicated with an arrow the direction of the magnetic field. This is just a consequence of whether the current is flowing out of the page or into the page. The direction can be determined by the Right-Hand Grip Rule: 1. Stick your thumb out and curl your fingers towards your palm. 2. Your thumb corresponds to the current direction, and the curling of your fingers represents the direction of the magnetic field.

When compasses are placed around the vertical wire, their needles point tangentially to the magnetic field, with North pointing in the same direction as the indicated arrow. Can you infer what the direction of the magnetic field is for a current going into the page? Solenoids and Electromagnets If a straight wire can generate a magnetic field, then a coil of wire ( solenoid ) can definitely also generate a magnetic field! However, the nature of this field is different. Remember that direction of current is taken conventionally , i.e. the flow of positive charges from the positive terminal, through the entire circuit, and ending at the negative terminal. Here, we may use the Right-Hand Grip Rule slightly differently: 1. Curl your fingers in the direction of the current looping in the coil. 2. Your thumb points in the direction in which the magnetic field leaves the loop, i.e. the North pole . The solenoid has a uniform magnetic field within it, and a