Question

31.8 According to Gauss's Law for Magnetic Fields, all magnetic field lines form a complete loop. Therefore, the direction of the magnetic field \(\vec{B}\) points from _________ pole to ________ pole outside of an ordinary bar magnet and from ____ pole to pole _______ inside the magnet. a) north, south, north, south b) north, south, south, north c) south, north, south, north d) south, north, north, south

Short answer

Answer: The correct directions of the magnetic field around a bar magnet are north to south outside the magnet and south to north inside the magnet.

Step-by-step solution

Recall Gauss's Law for Magnetic Fields

Gauss's Law for Magnetic Fields states that the net magnetic flux through any closed surface is zero. In other words, the number of magnetic field lines entering a closed surface must equal the number of magnetic field lines leaving that surface.

Understand magnetic field lines around a bar magnet

The magnetic field lines around a bar magnet form closed loops. Outside the magnet, the field lines go from the north pole to the south pole. Inside the magnet, the field lines continue to form a closed loop and go from the south pole to north pole.

Choose the correct option

Based on the understanding of magnetic field lines around a bar magnet, the correct option for this exercise is: b) north, south, south, north

Key concepts

Magnetic Field Lines

Magnetic field lines are a visual tool used to represent the strength and direction of a magnetic field. Their purpose is to illustrate how the field spreads out from a magnet and the way it influences the area around it. These lines start at the magnetic north pole and extend to the magnetic south pole, drawing a continuous loop that includes passing inside the material of the magnet.

Imagine these lines as closed paths, just like a running track, with no start or end point. The density of these lines indicates the strength of the magnetic field: The closer they are, the stronger the field. In the context of the question, recalling that these lines loop from the north pole to the south pole and back inside from south to north helps in correctly understanding the magnetic field's behavior.

Magnetic Flux

Magnetic flux is essentially the measure of the amount of magnetic field passing through a given area. It's a bit like counting the number of field lines that shoot through a camping tent's surface – the more lines that go through, the stronger the magnetic field inside. The unit for magnetic flux is the weber (Wb).

According to Gauss's Law for Magnetic Fields, the net magnetic flux through any closed surface—such as a sphere around a bar magnet—is always zero. This means that for every line entering this surface, another must be leaving. This principle is crucial for understanding advanced concepts in electromagnetism and helps to explain the behavior of magnetic fields in various applications, from electric motors to MRI machines.

Bar Magnet

A bar magnet is a classic example of a permanent magnet and is commonly used to demonstrate basic magnetic concepts. Picture it like a straight stick, with two distinct ends known as poles. One end is the north pole, and the other is the south pole. The magnet inherently contains a magnetic field around it, represented by the field lines we previously discussed.

The behaviour of its field lines, curving from one pole to the other, explains how magnets can attract certain metals or interact with other magnets (opposite poles attract, like poles repel). Understanding the structure and function of a bar magnet is foundational for learning about more complex magnetic structures and fields.

Magnetic Poles

Magnetic poles are the two ends of a magnet where the magnetic force is the strongest. These poles are labeled as 'north' and 'south' to indicate their orientation and the direction of the magnetic field they produce. Unlike electric charge, which can exist in isolation, magnetic poles always come in pairs: no magnetic monopoles have been found in nature.

When dealing with magnetic poles, it's important to remember that opposites attract: a north pole will pull toward a south pole, but two north poles (or two south poles) will repel each other. This concept is fundamental when predicting the movements and interactions of magnets in a given space or application.