An electromagnetic wave is transverse. This means the electric field E and the magnetic field B both vibrate at right angles (90 degrees) to the direction in which the wave moves, and E and B are also perpendicular to each other. Memory hook: think of the three fingers of your right hand at 90 degrees to each other, E, B and the direction of travel form the same three-way right angle.
In an EM wave the electric field E (red) and magnetic field B (blue, dashed) both oscillate perpendicular to the travel direction and to each other. Because the oscillating fields point sideways, not forward, the wave is transverse.
Your doubts, answered
Are electromagnetic waves transverse or longitudinal?
EM waves are transverse. In a transverse wave the vibration is perpendicular (at 90 degrees) to the direction the wave travels. In an EM wave both E and B point sideways to the path of the wave, so there is no back-and-forth vibration along the direction of travel. That is why sound (longitudinal) and light (transverse) are different in nature even though both are waves.
Why exactly are EM waves called transverse and not longitudinal?
Maxwell's equations show that the E field and B field of a plane EM wave have no component along the direction of propagation. They can only point sideways. Since the quantities that oscillate (E and B) are perpendicular to the travel direction, the wave fits the definition of a transverse wave. There is nothing vibrating forward and backward along the path.
What is actually vibrating in an EM wave if there is no medium?
In a mechanical transverse wave, particles of a medium move up and down. In an EM wave there are no particles vibrating. Instead the electric field E and the magnetic field B themselves grow and shrink in strength at each point. These field oscillations are perpendicular to the travel direction, so the wave is still transverse even in vacuum.
Are E and B perpendicular only to the travel direction, or to each other as well?
Both. E is perpendicular to the direction of travel, B is perpendicular to the direction of travel, and E is also perpendicular to B. So all three, E, B and the propagation direction, are mutually at right angles. The propagation direction points along E x B (the cross product of E and B).
Does the transverse nature let EM waves show polarisation?
Yes. Only transverse waves can be polarised, because a transverse vibration can be restricted to one plane. Light can be polarised, which is direct proof that light (an EM wave) is transverse. Longitudinal waves like sound cannot be polarised.
⚠️ The NEET trap ✗ Thinking E and B oscillate along the direction the wave travels, like a sound wave, so the wave is longitudinal. ✓ E and B oscillate perpendicular to the direction of travel and perpendicular to each other, so the EM wave is transverse. Only the wave itself moves forward; the fields point sideways. 🧠 NTA lists 'transverse in nature' as one of the TRUE properties in 'which is NOT a property' questions. If you mark it as the odd one out, you lose the mark. The false option is usually 'produced by charges moving with uniform speed'.
Real NEET questions
NEET 2024
The property which is NOT of an electromagnetic wave travelling in free space is that:
A · The energy density in the electric field is equal to the energy density in the magnetic field
B · They travel with a speed equal to 1/sqrt(mu0 x epsilon0)
C · They originate from charges moving with uniform speed ✓
D · They are transverse in nature
Solution: Step 1: Check each option against the known properties of a free-space EM wave. Step 2: Energy densities are equal, u_E = u_B, because E = cB makes (1/2)epsilon0 E^2 = B^2/(2 mu0). This is TRUE. Step 3: Speed = 1/sqrt(mu0 x epsilon0) = c. This is TRUE. Step 4: EM waves are transverse (E and B perpendicular to travel direction). This is TRUE. Step 5: EM waves are produced by ACCELERATING charges, not by charges moving at uniform speed. A uniform-speed charge gives only a steady magnetic field and no radiation. So option C is the property that is NOT of an EM wave. Answer: C.
NEET 2018
An EM wave is propagating in a medium with velocity V = V i-hat (along +x). The instantaneous oscillating electric field of this EM wave is along the +y axis. Then the direction of the oscillating magnetic field will be along:
A · -y direction
B · +z direction ✓
C · -z direction
D · -x direction
Solution: Step 1: For a transverse EM wave, E, B and the propagation direction are mutually perpendicular, and propagation is along E x B. Step 2: Given propagation along +x (i-hat) and E along +y (j-hat), we need E x B to point along +x. Step 3: Use the right-hand rule / unit vectors: j-hat x k-hat = i-hat. So if B is along +z (k-hat), then E x B = j-hat x k-hat = i-hat, which is +x. Correct. Step 4: Hence B oscillates along the +z direction. Answer: B. This question relies directly on the transverse, mutually perpendicular nature of E and B.
Solved Electromagnetic Waves NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. Light is an electromagnetic wave, and all EM waves are transverse. Its electric and magnetic fields vibrate at right angles to the direction the light travels. Polarisation of light is direct evidence of this transverse nature.
Can an EM wave be longitudinal?
No. Maxwell's equations force the E and B fields to have no component along the direction of travel. They can only point sideways, so an EM wave is always transverse, never longitudinal.
What does 'transverse' add that matters for NEET?
It tells you E, B and the propagation direction are mutually perpendicular. This is the base for E x B direction problems, polarisation questions, and 'which is NOT a property' MCQs, all of which appear regularly in NEET.
Do E and B stay perpendicular at every instant?
Yes. At every point and every instant, E is perpendicular to B, and both are perpendicular to the travel direction. They also rise and fall in step (in phase) with each other.
