Is Electromagnetic Waves part of the EAPCET Physics syllabus?

Yes. Electromagnetic Waves is taught in Intermediate second year Physics, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.

How many Physics questions are there in EAPCET?

40 of the 160 questions in the Engineering paper are Physics, spread across 30 chapters.

What mistakes do students make in Electromagnetic Waves?

Multiplying instead of dividing by c — B₀ = E₀/c, so the magnetic amplitude in tesla is very small. Thinking the E and B fields are 90° out of phase — in a travelling wave they oscillate in phase, but at right angles in space. Reversing the order of the spectrum — in increasing wavelength it runs gamma, X-ray, UV, visible, IR, microwave, radio. Treating displacement current as a flow of charges — it is a changing electric field, though it produces a magnetic field like a real current.

EAPCET Physics · Intermediate second year

Electromagnetic Waves

Electromagnetic Waves covers displacement current, the nature of electromagnetic waves and the electromagnetic spectrum.

Subject: Physics
Taught in: Intermediate second year
Physics in the paper: 40 of 160 questions

Key formulas and results

$c = \frac{1}{\sqrt{\mu_{0}\varepsilon_{0}}} \approx 3 \times 10^{8}\ \text{m/s}$
Displacement current: $I_{d} = \varepsilon_{0}\frac{d\Phi_{E}}{dt}$
$E_{0}/B_{0} = c$
Spectrum in increasing wavelength: gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, radio waves
Electromagnetic waves are transverse and carry energy and momentum
Plane wave along $x$ : $E = E_{0}\sin\omega(t - x/c)$ , $B = B_{0}\sin\omega(t - x/c)$ , with $\omega/k = c$
Speed in a medium: $v = \frac{1}{\sqrt{\mu\varepsilon}} = \frac{c}{\sqrt{\mu_{r}\varepsilon_{r}}}$
Average energy density: $u = \tfrac{1}{2}\varepsilon_{0}E_{0}^{2} = \frac{B_{0}^{2}}{2\mu_{0}}$ , shared equally between the electric and magnetic fields
Intensity: $I = u_{\text{avg}} \times c = \tfrac{1}{2}\varepsilon_{0}cE_{0}^{2} = \frac{E_{0}B_{0}}{2\mu_{0}}$
Poynting vector: $\vec{S} = \frac{\vec{E} \times \vec{B}}{\mu_{0}}$ , the energy crossing unit area per unit time ( $\text{W/m}^{2}$ )
Radiation pressure: $I/c$ on a perfect absorber and $2I/c$ on a perfect reflector; momentum delivered $p = U/c$
rms fields: $E_{\text{rms}} = E_{0}/\sqrt{2}$ and $B_{\text{rms}} = B_{0}/\sqrt{2}$
Maxwell’s equations: $\oint \vec{E}\cdot d\vec{S} = q/\varepsilon_{0}$ ; $\oint \vec{B}\cdot d\vec{S} = 0$ ; $\oint \vec{E}\cdot d\vec{l} = -\frac{d\Phi_{B}}{dt}$ ; $\oint \vec{B}\cdot d\vec{l} = \mu_{0}\left(I + \varepsilon_{0}\frac{d\Phi_{E}}{dt}\right)$

What this chapter covers

Displacement current
Properties of electromagnetic waves
The electromagnetic spectrum and its uses

How it is usually asked

Order or uses of parts of the spectrum
Displacement current
E and B amplitudes

Understanding Electromagnetic Waves

Maxwell noticed that Ampère’s law fails while a capacitor is charging, because no conduction current crosses the gap between the plates. He added a displacement current, ε₀ dΦ_E/dt, showing that a changing electric field produces a magnetic field just as a changing magnetic field produces an electric field. Together these effects allow self-sustaining electromagnetic waves.

In an electromagnetic wave, the electric and magnetic fields oscillate in phase, perpendicular to each other and to the direction of travel, so the wave is transverse. In vacuum it travels at c = 1/√(μ₀ε₀), and the field amplitudes are related by E₀ = cB₀. The waves need no medium and carry both energy and momentum.

The electromagnetic spectrum, from gamma rays to radio waves, is one family of waves that differ only in wavelength and frequency. Each band has typical sources and uses: gamma rays from nuclei, X-rays for medical imaging, ultraviolet for sterilisation, infrared for remote controls and heat lamps, microwaves for radar and ovens, and radio waves for broadcasting. EAPCET mostly asks about this order, these uses, displacement current and E₀/B₀.

Worked example

EAPCET-style question

The amplitude of the electric field of a plane electromagnetic wave in vacuum is 6 V/m. The amplitude of its magnetic field is ( $c = 3 \times 10^{8}\ \text{m/s}$ )

(1) $2 \times 10^{-8}\ \text{T}$
(2) $1.8 \times 10^{9}\ \text{T}$
(3)6 T
(4) $5 \times 10^{7}\ \text{T}$

Solution

For an electromagnetic wave in vacuum, $E_{0} = cB_{0}$ .
$B_{0} = \frac{E_{0}}{c} = \frac{6}{3 \times 10^{8}}$ .
$B_{0} = 2 \times 10^{-8}\ \text{T}$ .

Answer: $2 \times 10^{-8}\ \text{T}$

Shortcuts and results to remember

An electromagnetic wave travels in the direction of $\vec{E} \times \vec{B}$ .
Approximate frequency bands: microwaves $3 \times 10^{8}$ to $3 \times 10^{11}\ \text{Hz}$ (radar, microwave ovens), infrared $3 \times 10^{11}$ to $4 \times 10^{14}\ \text{Hz}$ (given out by hot bodies), visible light 4000 Å to 7000 Å.
Radio waves are produced by accelerated charges in wires (antennas) and are used for radio and television broadcasting.
Displacement current exists between the plates of a charging capacitor and keeps the current continuous through the gap.

Common mistakes to avoid

Multiplying instead of dividing by c — B₀ = E₀/c, so the magnetic amplitude in tesla is very small.
Thinking the E and B fields are 90° out of phase — in a travelling wave they oscillate in phase, but at right angles in space.
Reversing the order of the spectrum — in increasing wavelength it runs gamma, X-ray, UV, visible, IR, microwave, radio.
Treating displacement current as a flow of charges — it is a changing electric field, though it produces a magnetic field like a real current.

How to prepare it

Learn one use for each band of the spectrum — these are direct recall questions.

Once the formulas feel familiar, test them the way the exam does: practise Electromagnetic Waves questions chapter-wise, then attempt a full previous year paper to see whether it holds up under a 3-hour timer.

Related Physics chapters

See every chapter in the EAPCET Physics syllabus.

Practise Electromagnetic Waves chapter-wise

Chapter-wise quizzes show exactly which topics in this chapter you still get wrong — before a full paper does.

Frequently asked questions

Is Electromagnetic Waves part of the EAPCET Physics syllabus?: Yes. Electromagnetic Waves is taught in Intermediate second year Physics, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.
How should I prepare Electromagnetic Waves for EAPCET?: Learn one use for each band of the spectrum — these are direct recall questions.
How many Physics questions are there in EAPCET?: 40 of the 160 questions in the Engineering paper are Physics, spread across 30 chapters.
What mistakes do students make in Electromagnetic Waves?: Multiplying instead of dividing by c — B₀ = E₀/c, so the magnetic amplitude in tesla is very small. Thinking the E and B fields are 90° out of phase — in a travelling wave they oscillate in phase, but at right angles in space. Reversing the order of the spectrum — in increasing wavelength it runs gamma, X-ray, UV, visible, IR, microwave, radio. Treating displacement current as a flow of charges — it is a changing electric field, though it produces a magnetic field like a real current.