Physics · Class 12 Science
Ch 5Electromagnetic Waves — Class 12 Physics, concept-first.
We experience the universe almost entirely through light, yet for most of the 19th century physicists treated optics (the study of light) and electromagnetism (the study of electric and magnetic effects) as two separate branches of physics, connected only by coincidence. James Clerk Maxwell changed that.
Key concepts
Hover a concept to preview it and jump to its most relevant Q&A.
Speed Of Light
The speed of light is the speed at which light — and every other electromagnetic wave — travels through empty space (vacuum). It is one of the most important constants in physics, denoted :
Most relevant Q&A
Chapter contents
The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.
Introduction
We experience the universe almost entirely through light, yet for most of the 19th century physicists treated optics (the study of light) and electromagnetism (the study of electric and magnetic effec…
Displacement Current and Maxwell's Correction to Ampere's Circuital Law
Faraday's law says a changing magnetic flux through a loop induces an electric field around that loop: .
Maxwell's Equations in Integral Form
Maxwell's equations are the four fundamental laws of electrodynamics, playing a role for electromagnetism analogous to Newton's laws in mechanics: together they completely describe the behaviour of el…
Electromagnetic Waves
Bringing the previous section's four equations together, an electromagnetic wave is the coupled, self-sustaining disturbance of electric and magnetic fields that those equations predict must exist.
Production and Properties of Electromagnetic Waves
Maxwell's prediction of electromagnetic waves was experimentally confirmed by Heinrich Hertz in 1888 using an apparatus with two small spherical metal electrodes connected to an induction coil with a…
Sources of Electromagnetic Waves
Whether a charge radiates an electromagnetic wave depends entirely on how it moves. A stationary charge produces only a static (unchanging) electric field around it and nothing else.
Electromagnetic Spectrum
The electromagnetic spectrum is the complete, orderly arrangement of every possible electromagnetic wave, ordered by wavelength or, equivalently, by frequency -- since for any wave , a longer waveleng…
Types of Spectrum -- Emission and Absorption Spectrum -- Fraunhofer Lines
When an object is heated, it emits electromagnetic radiation whose character depends on its temperature: a moderately hot object glows red, a hotter one glows reddish-orange, and the hottest objects g…
SUMMARY
This unit's core results, gathered in one place: displacement current is the current that comes into play in any region where the electric field (or electric flux) is changing with time, defined as ;…
CONCEPT MAP
A one-glance map of how every topic in the unit connects back to the single root idea of 'Electromagnetic waves'.
EVALUATION
37 QThis evaluation section carries the unit's complete end-of-chapter assessment, split into four parts exactly as printed in the textbook: Part I, Multiple Choice Questions (15 questions, each with four…
+−I. Multiple Choice Questions15 questions
- Q1The dimension of $\dfrac{1}{\mu_0\epsilon_0}$ is (a) $[LT^{-1}]$ (b) $[L^2T^{-2}]$ (c) $[L^{-1}T]$ (d) $[L^{-2}T^2]$Free
- Q2If the amplitude of the magnetic field is $3\times10^{-6}$ T, then amplitude of the electric field for an electromagnetic wave is (a) 100 V…Free
- Q3Which of the following electromagnetic radiations is used for viewing objects through fog? (a) microwave (b) gamma rays (c) X-rays (d) infra…Free
- Q4Which of the following is false for electromagnetic waves? (a) transverse (b) non-mechanical waves (c) longitudinal (d) produced by accelera…Preview
- Q5Consider an oscillator which has a charged particle oscillating about its mean position with a frequency of 300 MHz. The wavelength of elect…Preview
- Q6The electric and the magnetic fields, associated with an electromagnetic wave, propagating along negative X axis can be represented by (a) $…Preview
- Q7In an electromagnetic wave travelling in free space the rms value of the electric field is 3 V m$^{-1}$. The peak value of the magnetic fiel…Preview
- Q8An e.m. wave is propagating in a medium with a velocity $\vec{v}=v\hat{i}$. The instantaneous oscillating electric field of this e.m. wave i…Preview
- Q9If the magnetic monopole exists, then which of the Maxwell's equations has to be modified? (a) $\displaystyle\oint \vec{E}\cdot d\vec{A}=\df…Preview
- Q10Fraunhofer lines are an example of _______ spectrum. (a) line emission (b) line absorption (c) band emission (d) band absorptionPreview
- Q11Which of the following is an electromagnetic wave? (a) $\alpha$ - rays (b) $\beta$ - rays (c) $\gamma$ - rays (d) all of themPreview
- Q12Which one of them is used to produce a propagating electromagnetic wave? (a) an accelerating charge (b) a charge moving with constant veloci…Preview
- Q13If $E=E_0\sin[10^6x-\omega t]$ be the electric field of a plane electromagnetic wave, the value of $\omega$ is (a) $0.3\times10^{-14}$ rad s…Preview
- Q14Which of the following is NOT true for electromagnetic waves? (a) it transports energy (b) it transports momentum (c) it transports angular…Preview
- Q15The electric and magnetic fields of an electromagnetic wave are (a) in phase and perpendicular to each other (b) out of phase and not perpen…Preview
+−II. Short Answer Questions8 questions
- Q1What is displacement current?Free
- Q2What are electromagnetic waves?Free
- Q3Write down the integral form of modified Ampere's circuital law.Free
- Q4Write notes on Gauss' law in magnetism.Preview
- Q5Give two uses each of (i) IR radiation, (ii) Microwaves and (iii) UV radiation.Preview
- Q6What are Fraunhofer lines? How are they useful in the identification of elements present in the Sun?Preview
- Q7Write notes on Ampere-Maxwell law.Preview
- Q8Why are e.m. waves non-mechanical?Preview
+−III. Long Answer Questions9 questions
- Q1Write down Maxwell equations in integral form.Free
- Q2Write short notes on (a) microwave (b) X-ray (c) radio waves (d) visible spectrumFree
- Q3Discuss the Hertz experiment.Free
- Q4Explain the Maxwell's modification of Ampere's circuital law.Preview
- Q5Explain the importance of Maxwell's correction.Preview
- Q6Write down the properties of electromagnetic waves.Preview
- Q7Discuss the source of electromagnetic waves.Preview
- Q8Explain the types of emission spectrum.Preview
- Q9Explain the types of absorption spectrum.Preview
+−IV. Numerical Problems5 questions
- Q1Consider a parallel plate capacitor whose plates are closely spaced. Let R be the radius of the plates and the current in the wire connected…Free
- Q2A transmitter consists of an LC circuit with an inductance of 1 $\mu$H and a capacitance of 1 $\mu$F. What is the wavelength of the electrom…Free
- Q3A pulse of light of duration $10^{-6}$ s is absorbed completely by a small object initially at rest. If the power of the pulse is $60\times1…Preview
- Q4Let an electromagnetic wave propagate along the x-direction. The magnetic field oscillates at a frequency of $10^{10}$ Hz and has an amplitu…Preview
- Q5If the relative permeability and relative permittivity of a medium are 1.0 and 2.25 respectively, find the speed of the electromagnetic wave…Preview
ICT Corner
A short ICT (Information and Communication Technology) activity box titled 'Physics of microwaves and heating food', directing the student to the free PhET interactive-simulation website (phet.colorad…
Sample & Board Papers
Sample papers and previous-year board questions for this subject.
+−Show 15 questionsHide questions15 questions
- Q1Write any three uses of infrared radiations.Preview
- Q2If $\mu_0$ and $\varepsilon_0$ are respectively the permeability and permittivity of free space, $\mu$ and $\varepsilon$ are the correspondi…Preview
- Q3Electromagnetic waves are : (a) may be transverse or longitudinal (b) transverse (c) neither transverse nor longitudinal (d) longitudinalPreview
- Q4Write the uses of infra-red rays.Preview
- Q5Charging current for a capacitor is 0.2 A, find the displacement current. (a) zero (b) 0.2 A (c) 0.4 A (d) 0.1 APreview
- Q6Which of the following is an electromagnetic wave ? (a) $\beta$-rays (b) $\gamma$-rays (c) $\alpha$-rays (d) All of the abovePreview
- Q7What is displacement current ?Preview
- Q8If the magnitude of the magnetic field is $3 \times 10^{-6}$ T, then the magnitude of the electric field for a electromagnetic wave is : (a)…Preview
- Q9An electromagnetic wave is propagating in a medium with velocity $\vec{v} = v\hat{i}$. The instantaneous oscillating electric field of this…Preview
- Q10(a) (i) Write down the properties of electromagnetic waves. (ii) The relative magnetic permeability of the medium is 2.5 and the relative el…Preview
- Q11If the amplitude of the magnetic field is $3 \times 10^{-6}$ T, then the amplitude of the electric field for a electromagnetic wave is : (a)…Preview
- Q12The dimension of $\dfrac{1}{\mu_0 \varepsilon_0}$ is : (a) $[L^{-1}T]$ (b) $[LT^{-1}]$ (c) $[L^{-2}T^2]$ (d) $[L^2T^{-2}]$Preview
- Q13Write down the properties of electromagnetic waves. (Any six)Preview
- Q14Which one of them is used to produce a propagating electromagnetic wave ? (a) a charge moving with constant velocity (b) an accelerating cha…Preview
- Q15Write down Maxwell equations in integral form. **OR** Derive the equation for angle of deviation produced by a prism.Preview