Characteristics and transverse nature of electromagnetic waves — practice questions

Question 1 · difficulty L1 · recall

Electromagnetic waves consist of oscillating

• A. pressure and density only
• B. electric charge and mass density only
• C. electric and magnetic fields
• D. gravitational potential only

Question 2 · difficulty L1 · understanding

In an electromagnetic wave in vacuum, E and B are

• A. parallel to each other
• B. both longitudinal
• C. randomly oriented with no relation
• D. perpendicular to each other and to the direction of propagation

Question 3 · difficulty L2 · understanding

The speed of electromagnetic waves in vacuum is

• A. c = 1/sqrt(μ0ε0)
• B. sqrt(μ0ε0)
• C. μ0/ε0
• D. 1/(μ0ε0)

Question 4 · difficulty L2 · application

For a plane electromagnetic wave in vacuum, the field amplitudes satisfy

• A. E0B0=c
• B. E0/B0 = c
• C. E0/B0=1/c
• D. E0=B0 in identical SI units

Question 5 · difficulty L3 · application

Electromagnetic waves can propagate through vacuum because

• A. they are mechanical vibrations of air
• B. vacuum contains ordinary sound particles
• C. they do not require a material medium
• D. they require conduction current everywhere

Question 6 · difficulty L3 · application

If the electric field of a plane wave points along +y and the magnetic field along +z, the wave propagates along

• A. -x
• B. +y
• C. -z
• D. +x

Question 7 · difficulty L3 · understanding

The electric field in a plane electromagnetic wave is given by $$E_z=60 \cos \left(5 x+1.5 \times 10^9 t\right) \mathrm{V} / \mathrm{m}$$ Then expression for the corresponding magnetic field is (here subscripts denote the direction of the field) :

• A. $B z=60 \cos \left(5 x+1.5 \times 10^9 t\right) T$
• B. $B_y=60 \sin \left(5 x+1.5 \times 10^9 t\right) T$
• C. $B_y=2 \times 10^{-7} \cos \left(5 x+1.5 \times 10^9 t\right) T$
• D. $B_x=2 \times 10^{-7} \cos \left(5 x+1.5 \times 10^9 t\right) T$

Question 8 · difficulty L3 · understanding

If the ratio of relative permeability and relative permittivity of a uniform medium is $$1: 4$$. The ratio of the magnitudes of electric field intensity $$(E)$$ to the magnetic field intensity $$(H)$$ of an EM wave propagating in that medium is (Given that $$\sqrt{\frac{\mu_0}{\varepsilon_0}}=120 \pi$$):

• A. $$30 \pi: 1$$
• B. $$1: 120 \pi$$
• C. $$60 \pi: 1$$
• D. $$120 \pi: 1$$

Question 9 · difficulty L3 · understanding

The property which is not of an electromagnetic wave travelling in free space is that:

• A. They are transverse in nature
• B. The energy density in electric field is equal to energy density in magnetic field
• C. They travel with a speed equal to $$\frac{1}{\sqrt{\mu_0 \varepsilon_0}}$$
• D. They originate from charges moving with uniform speed

Question 10 · difficulty L3 · understanding

In a plane electromagnetic wave travelling in free space, the electric field component oscillates sinusoidally at a frequency of $$2.0 \times 10^{10} \mathrm{~Hz}$$ and amplitude $$48 ~\mathrm{Vm}^{-1}$$. Then the amplitude of oscillating magnetic field is : (Speed of light in free space $$=3 \times 10^{8} \mathrm{~m} \mathrm{~s}^{-1}$$ )

• A. $$1.6 \times 10^{-8} \mathrm{~T}$$
• B. $$1.6 \times 10^{-7} \mathrm{~T}$$
• C. $$1.6 \times 10^{-6} \mathrm{~T}$$
• D. $$1.6 \times 10^{-9} \mathrm{~T}$$