Which of the followings are the characteristics of electromagnetic waves? 1) They are elastic waves. 2) They can also move in a vacuum. 3) They have electric and magnetic components that are mutually perpendicular. 4) They move with a speed equal to 3 lakh meters per second. Select the correct answer using the code given below:
2 and 3 only
Understanding Electromagnetic Waves
Electromagnetic waves are a fascinating type of wave that play a crucial role in transmitting energy throughout the universe. Unlike some other types of waves, electromagnetic waves have unique characteristics that allow them to travel over vast distances and through different media, including the vacuum of space.
Let's carefully examine each statement given in the question to determine which ones accurately describe the characteristics of electromagnetic waves.
Analysis of Statements on Electromagnetic Wave Characteristics
Statement 1: They are elastic waves.
This statement is incorrect. Elastic waves, such as sound waves or seismic waves, require a material medium (like air, water, or solid rock) to propagate. They travel by causing vibrations in the atoms or molecules of the medium. Electromagnetic waves, on the other hand, do not require a medium. They can travel through a vacuum, which is a key difference from elastic waves. Therefore, electromagnetic waves are not elastic waves.
Statement 2: They can also move in a vacuum.
This statement is correct. One of the defining characteristics of electromagnetic waves is their ability to travel through a vacuum. This is how light from the sun reaches Earth, or how radio signals travel through space. They do not need air or any other material to propagate.
Statement 3: They have electric and magnetic components that are mutually perpendicular.
This statement is correct. An electromagnetic wave consists of oscillating electric and magnetic fields. These fields are always perpendicular to each other and also perpendicular to the direction in which the wave is traveling. This transverse nature is a fundamental property of electromagnetic waves.
We can visualize this as:
- Electric field oscillates along one axis (e.g., y-axis).
- Magnetic field oscillates along another axis (e.g., z-axis), perpendicular to the electric field.
- The wave propagates along the third axis (e.g., x-axis), perpendicular to both fields.
Statement 4: They move with a speed equal to 3 lakh meters per second.
This statement is incorrect regarding the standard speed of electromagnetic waves in a vacuum. The speed of electromagnetic waves in a vacuum is constant and is approximately $3 \times 10^8$ meters per second. The value given, 3 lakh meters per second, is equal to $3 \times 10^5$ meters per second, which is much slower than the actual speed of light. The correct speed is $3 \times 10^8$ m/s, which is also referred to as 3 lakh kilometers per second (300,000 km/s) or 30 crore meters per second (300,000,000 m/s).
Identifying the Correct Characteristics
Based on our analysis:
- Statement 1 is false (Electromagnetic waves are not elastic waves).
- Statement 2 is true (Electromagnetic waves can move in a vacuum).
- Statement 3 is true (Electromagnetic waves have mutually perpendicular electric and magnetic components).
- Statement 4 is false (The speed is approximately $3 \times 10^8$ m/s, not $3 \times 10^5$ m/s).
Therefore, the correct characteristics listed are statements 2 and 3.
Conclusion on Electromagnetic Wave Properties
The properties that correctly describe electromagnetic waves from the given list are that they can travel in a vacuum and have electric and magnetic fields perpendicular to each other. Looking at the options, the one that includes only statements 2 and 3 is the correct answer.
| Statement | Accuracy | Explanation |
|---|---|---|
| 1) They are elastic waves. | Incorrect | Electromagnetic waves do not require a medium; elastic waves do. |
| 2) They can also move in a vacuum. | Correct | A defining characteristic; they travel at the speed of light in vacuum. |
| 3) They have electric and magnetic components that are mutually perpendicular. | Correct | The electric and magnetic fields are perpendicular to each other and to the direction of propagation. |
| 4) They move with a speed equal to 3 lakh meters per second. | Incorrect | The speed in vacuum is approx. $3 \times 10^8$ m/s, not $3 \times 10^5$ m/s. |
Revision Table: Key Electromagnetic Wave Properties
| Property | Description |
|---|---|
| Medium Requirement | Do not require a medium; can travel through vacuum. |
| Nature | Transverse waves (fields perpendicular to propagation). |
| Components | Consist of oscillating electric and magnetic fields. |
| Field Orientation | Electric and magnetic fields are mutually perpendicular and perpendicular to propagation. |
| Speed in Vacuum | Constant speed, $c \approx 3 \times 10^8$ m/s (speed of light). |
| Energy & Momentum | Carry energy and momentum. |
| Examples | Light, radio waves, microwaves, X-rays, gamma rays. |
Additional Information on Electromagnetic Waves
Electromagnetic waves are produced by accelerating electric charges. They carry energy and momentum, and they obey the principles of superposition and diffraction. The entire range of different types of electromagnetic waves, ordered by frequency or wavelength, is known as the electromagnetic spectrum. This spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.
The speed of electromagnetic waves depends on the medium they are traveling through. In vacuum, their speed is the speed of light, denoted by $c$. In materials, the speed is lower than $c$ and is given by $v = c/n$, where $n$ is the refractive index of the material.
Important Questions from Electromagnetic Waves
Consider the two statements given below :
Statement-1: Infrared waves are also called heat waves.
Statement-2: Water molecules readily absorb infrared waves.
Select the correct answer using the code given below:
Consider the following statements about visible light, UV light and X-rays:
1. The wavelength of visible light is more than that of X-rays.
2. The energy of X-ray photons is higher than that of UV light photons.
3. The energy of UV light photons is less than that of visible light photons.
Which of the statements given above is/are correct?The wavelength of X-rays is of the order of
Which of the following devices is based on the phenomenon of electromagnetic induction?
Which factor does NOT affect the magnitude of motional EMF in a conductor?
