NCERT Solutions Class 12th Physics Chapter – 8 Electromagnetic Waves
| Textbook | NCERT |
| class | Class – 12th |
| Subject | Physics |
| Chapter | Chapter – 8 |
| Chapter Name | Electromagnetic Waves |
| Category | Class 12th Physics Notes in English |
| Medium | English |
| Source | Last Doubt |
NCERT Solutions Class 12th Physics Chapter – 8 Electromagnetic Waves
?Chapter – 8?
✍Electromagnetic Waves✍
?Notes?
Displacement current is a 1 ways equal to charging (for discharging) current and lasts so long as the capacitor (producing varying electric field) is charged or discharged.
An accelerated charged particle emits e.m. waves.
S→ = E→ × B→ is called Poynting vector acts in a direction perpendicular to the plane of E→ and B→ .
The displacement current is named so because it is produced by the displacement of electrons caused by changing electric fields.
X-rays have the shortest wavelength (≈ 1 Å).
The charging or discharging current is called conduction current.
The amplitude of electric and magnetic fields in free space in e.m. waves are related as E = CB
Electric vector is called light vector as it is responsible for the optical effect of e.m. wave.
The energy of the e.m. wave is shared equally between the electric field vector and the magnetic field vector.
Microwaves are very commonly used in radar to locate flying objects like airplanes, jet planes, etc.
Tire earth’s atmosphere produces Green House effect. In the absence of the earth’s atmosphere, the temperature on earth during the day will increase and during the night it would decrease.
The ozone layer which is present in the stratosphere protects the earth from high-energy radiations coming from outer space.
The velocity of em. waves in a medium is given by
v = 1μ0ε0μrεr√=Cμrεr√
There is no conduction current in a traveling e.m. wave.
Earth’s atmosphere is transparent to visible light and most of the infrared rays are absorbed by the atmosphere.
Radio waves were discovered by Hertz and are used in communication.
e.m. waves are transverse in nature.
e.m. waves exert pressure on the objects on which they fall as they carry energy and momentum.
The wavelength range of em. waves are from 10-15 m to 109 m and the frequency range is 1024 Hz to 1 Hz.
Green House Effect takes place due to the heating of the earth’s atmosphere due to the trapping of infrared rays by the CO2 layer in the atmosphere.
Modified Ampere Circuital law – It states that the line integral of the magnetic field around a closed path is always equal to μ0 times the sum of the conduction dnd displacement currents i.e.,
Displacement Current – It is defined as the current produced in a region where a change of electric flux takes place due to the change in electric field intensity in that region.
Important Formulae
Amper’s circuital law states that
∫ B→.dl→ = μ0 IC
where IC = conduction current Displacement current is given by
Displacement current is given by
ID = ε0 dϕEdt
C = E0B0=1μ0ε0√
Energy density of electric field, UE = 12 ε0 E2
Energy density of electric field, UB = B22μ20
Intensity of e.m. wave is given by
I = average energy density × speed of e.m. wave
= 12 ε0E2 × C = ρ/4πr²
B→ at a point between the plates of the capacitor at a distance r from its axis is given by.
B = μ0Ir2πR2
Where R = radius of each circular plate of the capacitor.
Velocity of e.m. waves is
C = vλ
An electromagnetic wave of frequency v, wavelength λ propagating along the z-axis, we have
The speed of light or of electromagnetic waves in a material medium is given by
υ = 1με√
where μ is the permeability of the medium and ε is its permittivity.
Bmax = μ0ID2πR