Differences Between Mechanical Waves and Electromagnetic Waves

What is the main difference between mechanical and electromagnetic waves?

Main Difference Between Mechanical and Electromagnetic waves

A wave is composed of some kind of disturbance that propagates. We can classify waves into many different types based on their properties. One of the properties of the waves depends on whether they need a medium to propagate or not. The primary difference between electromagnetic and mechanical waves is also based on this property. Mechanical waves need a medium, while electromagnetic waves do not need a medium to propagate. Electromagnetic waves can travel through a vacuum. The other differences between mechanical and electromagnetic waves are given below:

• Electromagnetic waves can travel through a vacuum, that is an empty space, whereas mechanical waves cannot. They need a medium to travel such as water or air. Ripples in a pond are an example of mechanical waves whereas electromagnetic waves include light and radio signals, which can travel through the vacuum of space.
• Mechanical waves can be classed as elastic waves because their transmission depends on the medium's (water, air etc.) elastic properties.
• Electromagnetic waves are caused because of the varying magnetic and electric fields. They are produced by the vibration of the charged particles.
• Because of these differences, the speed of each type of wave varies significantly. Electromagnetic waves travel at the speed of light but mechanical waves are far slower.
• Electromagnetic waves are called a disturbance, and mechanical waves are known as a periodic disturbance.

What are Mechanical and Electromagnetic Waves?

In this section, we will discuss mechanical and electromagnetic waves in detail.

Mechanical waves

Mechanical waves are made up of disturbances that require a medium to propagate. For instance, if you wiggle a rope up and down, you will see a wave. This is known as a mechanical wave. This type of wave is created from the movement of one molecule which causes the movement of other molecules in the same direction. You may be wondering what is the medium of propagation in this case. Well, the medium of propagation is the rope because the movement of its molecules carries the disturbance along. Sound waves are also a perfect example of mechanical waves. They are composed of oscillating molecules. We hear a sound when our ears identify the back and forth movement of air molecules. Our brain deciphers this movement of air molecules as sound. Have you ever wondered how do we hear sound underwater? The answer is simple. When we are above the ground, we hear sound due to vibrations in air molecules, whereas underwater the hearing becomes possible due to the vibration of water molecules.

Electromagnetic waves

Electromagnetic waves are composed of disturbances that can propagate in the absence of a medium. For instance, light is an example of an electromagnetic wave. Light from the sun propagates through a vacuum between the earth and the sun. Electromagnetic waves depend on the electric field to travel instead of the vibrating molecules. In addition to an electric field, a magnetic field also exists which oscillates in phase at 90 degrees to the electric field. All the electromagnetic fields in the vacuum propagate at the speed of $3 \times 10^8m s^{-1}$. This is often referred to as the speed of light in a vacuum. The classification of waves depends on what medium they use for propagation and how energy moves through them.

How are Waves Being Classified?

The classification of waves depends on what medium they use for propagation and how energy moves through them.

Classification based on the medium

Based on the medium, the waves are classified as mechanical or electromagnetic waves.  The medium of the wave also defines the speed of the waves. For instance, mechanical waves such as sound waves travel faster through solids because the molecules in the solid structures are compactly arranged. On the other hand, electromagnetic waves like light waves travel faster in a vacuum than in solids.

Classification based on how energy moves through them

There are two different types of waves based on how energy moves through them. These two types are compressional or longitudinal waves and transverse waves.

What are Types of Waves?

There are many types of waves in physics. Although they have many things in common, however, they exhibit certain behaviors and characteristics that can distinguish them from each other. Depending upon the particle of motion and energy direction, waves in physics are divided into the following three categories:

• Electromagnetic waves
• Mechanical waves
• Matter waves

Electromagnetic waves Examples of electromagnetic waves are light, infrared, X-rays, radio waves, and ultraviolet rays. Mechanical waves Mechanical waves are further divided into two main categories:

• Longitudinal waves
• Transverse waves

Matter waves This type of wave is complicated to comprehend and was first discovered by the founder of Quantum Physics. It is based on the dual nature of the matter. Matter can exist both as a wave and as a particle.

What is the Difference Between Longitudinal and Transverse Waves?

Longitudinal Wave Definition

Longitudinal wave refers to a wave in which the vibration or periodic disturbance occurs in the same direction as the movement of the wave.

Examples of longitudinal waves are ultrasound waves, sound waves, and seismic P-waves. To understand a longitudinal wave, consider a coiled spring that is compressed at one end and then released. This spring undergoes a wave of compression that propagates its length. When it is followed by stretching, a point on the coil of the spring moves with a wave and returns along the same path. In other words, the coil passes through the neutral position and reverses its motion again. You can remember the motion of particles in the longitudinal waves using a "P" sound. Longitudinal waves like seismic P-waves can be considered as push or pressure waves as the particles move parallel to the wave. Longitudinal waves demonstrate regions of compression and rarefaction. Compression refers to the areas of higher pressure due to the closeness of particles. Rarefactions reflect the areas of low pressure because of the particle moving apart from each other.

Transverse wave definition