Have you ever wondered why materials such as magnets exist, and how they work? Well, the principles behind it makes it a rather interesting subject. A magnetic field is produced by electric currents which are caused by the interaction of two or more magnetic objects, with similar or opposite poles. Applications of electromagnets and their fields are numerous. Some examples for the use of magnets include: Credit cards, recording videotapes, speakers, and even doorbells.
The Right Hand Grip Rule
We use the right hand rule to determine which direction the magnetic field is going. There are generally two rules that we can use. The first method involves pointing your index finger in the direction of the current, with your middle finger pointing in the direction of the magnetic field (out of the paper), and your thumb pointing in the direction of the magnetic force.
The second method is used to determine the direction of the magnetic field around a wire which has a current flowing through it. For this method, you should curl your fingers at least halfway around the wire, which point in the direction of the magnetic field, while pointing your thumb in the direction of the current.
Magnetic Field Strength
To determine the strength of a magnetic field, we use the Tesla (T) unit, in the SI system. One Tesla is equal to 1 Newton per ampere meter. There are also other methods to calculate Tesla, such as kilograms per coulomb second, or joules per ampere squared meter.
The magnetic field strength of a straight wire, with a current running through it, is relatively weak. If loops are wound along the same axis, however, the magnetic field strength of the wire will become more concentrated. Thus, a wire with several loops generates an electromagnetic coil commonly referred to as a solenoid.
Our planet has a magnetic field that is not too different from that of a bar magnet, except that the Earth’s magnetic field changes over time due to the motion of molten metals in the outer core. This flow of molten metals is what produces electric currents. The Earth’s magnetic field functions to protect us against solar wind and radiation from outer space.
We will discuss more during our JC Physics tuition classes. Alternatively, you can refer to books such as Cutnell, J., Johnson, K. (1998). Physics, Vol. 2, Wiley: NY, pp. 631, 33, 46, and 49 and Halliday, Resnick and Walker, J. (2011). Principles of Physics, ninth edition, Wiley, p. 720.