Waves consisting of oscillating electric and magnetic fields, perpendicular to each other and to the direction of propagation.
Like WiFi signals zipping through your room invisibly — that’s EM waves.
The speed of EM waves in a vacuum.
PYQ Type: Value / formula MCQ
Characteristics of electromagnetic waves.
PYQ Type: Concept theory MCQ
The range of electromagnetic waves in order of frequency and wavelength.
| Wave Type | Frequency | Wavelength |
|---|---|---|
| Radio waves | Lowest | Longest |
| Microwaves | ↑ | ↓ |
| Infrared | ↑ | ↓ |
| Visible | ↑ | ↓ |
| Ultraviolet | ↑ | ↓ |
| X-rays | ↑ | ↓ |
| Gamma rays | Highest | Shortest |
PYQ Type: Arrange / identify MCQ
Practical applications of different EM waves.
| Wave | Use |
|---|---|
| Radio | Broadcasting |
| Microwaves | Cooking, radar |
| Infrared | Night vision, remote |
| Visible | Seeing |
| UV | Sterilization |
| X-rays | Medical imaging |
| Gamma | Cancer treatment |
PYQ Type: Possible question zone
2021 Shift 2: Speed of EM wave MCQ
2022 Shift 3: Nature of EM waves theory
2023 Feb Shift 1: Arrange EM waves in increasing frequency
| Formula | Meaning |
|---|---|
| \( c = \frac{1}{\sqrt{\mu_0 \epsilon_0}} \) | Speed of EM waves |
| \( c = 3 \times 10^8 \, \text{m/s} \) | Speed in vacuum |
| Concept | GenZ Example |
|---|---|
| EM waves = E and B fields oscillating perpendicular | WiFi or mobile signals |
| EM spectrum: Radio to Gamma rays | From FM radio to radiation therapy |
| All EM waves move at 3 × 10⁸ m/s in vacuum | Light, X-rays, UV — all same speed in air |
Focus Areas:
Q1. Speed of EM waves in vacuum is:
a) 3 × 10⁸ m/s
b) 3 × 10⁶ m/s
c) 1 × 10⁸ m/s
d) 5 × 10⁸ m/s
Ans: a
Q2. EM waves are:
a) Longitudinal
b) Transverse
c) Circular
d) None
Ans: b
Q3. Which of these has highest frequency?
a) Radio waves
b) X-rays
c) Gamma rays
d) UV rays
Ans: c
Q4. Which waves are used in cooking ovens?
a) UV rays
b) X-rays
c) Microwaves
d) Gamma rays
Ans: c
Q5. Arrange in increasing frequency:
Radio, Infrared, X-rays, Gamma rays
Ans: Radio < Infrared < X-rays < Gamma
Q6. Formula for speed of EM waves in vacuum:
a) 1 / √(μ₀ε₀)
b) μ₀ / ε₀
c) ε₀ / μ₀
d) 1 / (μ₀ε₀)
Ans: a
Q7. Which wave is used for sterilizing instruments?
a) X-rays
b) UV rays
c) Gamma rays
d) Microwaves
Ans: b
Q8. Magnetic and electric fields in EM wave are:
a) Parallel
b) Perpendicular
c) Opposite
d) None
Ans: b
Q9. Unit of μ₀ (permeability of free space) is:
a) T m/A
b) N/C
c) J/C
d) V
Ans: a
Q10. Gamma rays are mainly used in:
a) Broadcasting
b) Medical therapy
c) Cooking
d) Remote controls
Ans: b