1.The current that comes into play in a region where the electric field is changing...
Ans: Displacement
2.The theoretical inconsistency in Ampere's circuital law was pointed out and corrected by...
Ans: James Clerk Maxwell
3.The mathematical formula for displacement current ($I_d$) is:
Ans: (B) $\epsilon_0 \frac{d\Phi_E}{dt}$
4.What is the standard SI unit of displacement current?
Ans: Ampere ($\text{A}$). Just like conduction current, it is measured in Amperes.
5.What is the value of the regular conduction current ($I_c$) strictly *between* the plates?
Ans: Zero ($0$). There are no physical charge carriers moving through the insulating gap between the plates.
6.State the generalized Ampere-Maxwell circuital law equation.
Ans: $\oint \vec{B} \cdot d\vec{l} = \mu_0(I_c + I_d) = \mu_0 \left( I_c + \epsilon_0 \frac{d\Phi_E}{dt} \right)$.
7.Does displacement current behave like a source of magnetic field?
Ans: Yes. A changing electric field (displacement current) produces a magnetic field exactly like a physical conduction current does.
8.Calculate displacement current for $d\Phi_E/dt = 10^{12}$.
Ans: $I_d = \epsilon_0 \frac{d\Phi_E}{dt} = (8.85 \times 10^{-12}) \times 10^{12} = 8.85\text{ A}$.
9.In a steady DC circuit, displacement current is exactly...
Ans: Zero. (Because the electric field is constant, $d\Phi_E/dt = 0$).
10.Continuity of current is maintained by adding the concept of...
Ans: Displacement current. (So that $I = I_c + I_d$ is continuous throughout the entire circuit).
11.Match the current types to their physical causes:
Ans: (a) Conduction Current $\rightarrow$ (ii) Flow of physical charge carriers
(b) Displacement Current $\rightarrow$ (i) Changing electric flux
12.Gauss's law for magnetism: net magnetic flux is always...
Ans: Zero.
13.Equation signifies the non-existence of isolated magnetic...
Ans: Monopoles. (Magnetic poles always exist in North-South pairs).
14.Which of Maxwell's equations is $\oint \vec{E} \cdot d\vec{l} = -\frac{d\Phi_B}{dt}$?
Ans: (C) Faraday's law of induction.
15.Write the integral form of Gauss's Law for Electrostatics.
Ans: $\oint \vec{E} \cdot d\vec{A} = \frac{Q}{\epsilon_0}$.
16.Name the equation that states a changing electric field produces a magnetic field.
Ans: Ampere-Maxwell Law.
17.What does $q$ physically represent in Gauss's law?
Ans: The net electric charge enclosed strictly *inside* the closed Gaussian surface.
18.Which two laws prove changing E and B fields act as sources for each other?
Ans: Faraday's Law (changing B creates E) and the Ampere-Maxwell Law (changing E creates B).
19.Maxwell's equations along with the ____________ force law summarize electromagnetism.
Ans: Lorentz (Force law: $\vec{F} = q(\vec{E} + \vec{v} \times \vec{B})$).
20.Match Maxwell's equations to phenomena:
Ans: (a) $\oint \vec{B} \cdot d\vec{A} = 0 \rightarrow$ (iii) Magnetic monopoles do not exist.
(b) $\oint \vec{E} \cdot d\vec{A} = Q/\epsilon_0 \rightarrow$ (i) Charges create electric fields.
(c) $\oint \vec{E} \cdot d\vec{l} = -d\Phi_B/dt \rightarrow$ (ii) Changing magnetic flux creates EMF.
21.Electromagnetic waves are ____________ in nature.
Ans: Transverse.
22.The oscillating electric field and magnetic field are strictly ____________ to each other.
Ans: Perpendicular (or Orthogonal).
23.The speed of an EM wave in a vacuum ($c$) is given by:
Ans: (B) $1 / \sqrt{\mu_0 \epsilon_0}$.
24.Relation between $E_0, B_0$, and $c$.
Ans: $c = \frac{E_0}{B_0}$ (Ratio of electric field amplitude to magnetic field amplitude equals the speed of light).
25.Peak E is $300\text{ V/m}$. Calculate peak B.
Ans: $B_0 = \frac{E_0}{c} = \frac{300}{3 \times 10^8} = 100 \times 10^{-8} = 10^{-6}\text{ Tesla}$ ($1\text{ }\mu\text{T}$).
26.Direction of propagation given by which cross product?
Ans: $\vec{E} \times \vec{B}$.
27.Do EM waves require a material medium?
Ans: No. They can travel perfectly through a vacuum.
28.EM waves carry both energy and...
Ans: Momentum.
29.Formula for momentum ($p$) carried by EM wave.
Ans: $p = \frac{U}{c}$ (where $U$ is total energy transferred and $c$ is speed of light).
30.Force per unit area is called radiation...
Ans: Pressure.
31.How is energy divided between E and B fields?
Ans: It is divided equally. The average electric energy density is exactly equal to the average magnetic energy density ($u_E = u_B$).
32.Phase difference between E and B fields in vacuum?
Ans: Zero. They are perfectly in phase (they reach their maximum and zero values simultaneously).
Ans: (a) Produced by $\rightarrow$ (ii) Accelerating/Oscillating charges.
(b) Nature of wave $\rightarrow$ (i) Transverse.
(c) Speed in vacuum $\rightarrow$ (iii) $3 \times 10^8\text{ m/s}$.
34.Speed in medium with $\epsilon_r = 4, \mu_r = 1$.
Ans: Refractive index $n = \sqrt{\mu_r \epsilon_r} = \sqrt{1 \times 4} = 2$.
Speed $v = \frac{c}{n} = \frac{3 \times 10^8}{2} = 1.5 \times 10^8\text{ m/s}$.
35.Formula for average electric energy density ($u_E$).
Ans: $u_E = \frac{1}{4} \epsilon_0 E_0^2$ (or $\frac{1}{2} \epsilon_0 E_{rms}^2$).
36.Orderly arrangement is called Electromagnetic...
Ans: Spectrum.
37.Which EM wave has the longest wavelength?
Ans: Radio waves.
38.Which EM wave has the highest frequency and energy?
Ans: Gamma ($\gamma$) rays.
39.Which comes right after Infrared moving towards higher frequency?
Ans: Visible Light.
40.Standard relation between $c, f, \lambda$.
Ans: $c = f \lambda$ (or $c = \nu \lambda$).
41.Which are known as "Heat Waves"?
Ans: (C) Infrared waves.
42.State one prominent use of Microwaves.
Ans: Microwave ovens for cooking, or RADAR systems, or satellite communication.
43.Which rays are used in medical diagnostics for bones?
Ans: X-rays.
44.Wave used in standard RADAR systems?
Ans: Microwaves.
Ans: Germs / Bacteria / Microorganisms.
46.Portion the human eye can detect is called...
Ans: Visible.
47.Produced by rapid deceleration of fast electrons on heavy metal.
Ans: X-rays.
48.Emitted by radioactive nuclei?
Ans: Gamma rays.
49.Calculate frequency of radio wave of $300\text{ m}$.
Ans: $f = \frac{c}{\lambda} = \frac{3 \times 10^8}{300} = 10^6\text{ Hz}$ ($1\text{ MHz}$).
50.Waves used in TV and FM broadcasting.
Ans: Radio waves.
Ans: (a) Infrared $\rightarrow$ (iii) TV remote controls / Night vision.
(b) Ultraviolet $\rightarrow$ (i) LASIK / Water purification.
(c) Gamma rays $\rightarrow$ (ii) Cancer treatment.
52.Approx wavelength range of Visible Light?
Ans: $400\text{ nm}$ to $700\text{ nm}$ (or $4000\text{ \AA}$ to $7000\text{ \AA}$).
53.Which layer absorbs harmful UV?
Ans: Ozone layer (in the stratosphere).
54.Why Microwaves for satellite links?
Ans: Due to their short wavelengths, they can penetrate the Earth's ionosphere without being reflected or heavily absorbed, reaching satellites effectively.
55.True or false: All EM waves travel at the same speed in vacuum.
Ans: True. ($3 \times 10^8\text{ m/s}$).
56.Which color has longest wavelength?
Ans: Red.
57.Which color has highest frequency?
Ans: Violet.
58.Increasing order of energy: X-rays, Visible, Microwaves.
Ans: Energy increases with frequency. Order: Microwaves $<$ Visible light $<$ X-rays.
59.Wavelength of X-ray with $f = 3 \times 10^{18}\text{ Hz}$.
Ans: $\lambda = \frac{c}{f} = \frac{3 \times 10^8}{3 \times 10^{18}} = 10^{-10}\text{ m}$ ($1\text{ \AA}$).
60.Electronic tubes used to produce Microwaves.
Ans: Klystrons, Magnetrons, or Gunn diodes.
