Electromagnetic Waves Flashcards for NEET — 20 cards

First 8 of 20 Electromagnetic Waves flashcards

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1. Card 1 of 20

   What is the formula for the speed of an EM wave in a vacuum and in a material medium?

   Hint: Depends on permeability ($\mu$) and permittivity ($\epsilon$).

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   Answer

   Vacuum: $c = \frac{1}{\sqrt{\mu_0 \epsilon_0}}$ \nMedium: $v = \frac{1}{\sqrt{\mu \epsilon}}$

2. Card 2 of 20

   What is the relationship between the amplitudes of the Electric ($E_0$) and Magnetic ($B_0$) fields in an EM wave?

   Hint: The ratio of their magnitudes equals the speed of light.

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   Answer

   Because $c = 3 \times 10^8$ m/s, the electric field amplitude is much larger than the magnetic field amplitude.

3. Card 3 of 20

   Define the concept and write the formula for Displacement Current.

   Hint: Maxwell's missing puzzle piece for Ampere's Law.

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   Answer

   $I_d = \epsilon_0 \frac{d\Phi_E}{dt}$

   Where $\Phi_E$ is the electric flux.

4. Card 4 of 20

   State the Ampere-Maxwell Law.

   Hint: Generalization of Ampere's circuital law.

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   Answer

   $\oint \vec{B} \cdot d\vec{l} = \mu_0 (I_c + I_d) = \mu_0 (I_c + \epsilon_0 \frac{d\Phi_E}{dt})$

5. Card 5 of 20

   What is the primary source of Electromagnetic Waves?

   Hint: Charges at rest produce E-fields; steady currents produce B-fields. What produces both?

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   Answer

   An accelerating (or oscillating) electric charge.

6. Card 6 of 20

   How do you determine the direction of propagation of an EM wave?

   Hint: Poynting vector direction.

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   Answer

7. Card 7 of 20

   How is the total average energy density of an EM wave shared between the electric and magnetic fields?

   Hint: Symmetry in energy.

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   Answer

   $U_{total} = U_E + U_B = \frac{1}{2}\epsilon_0 E_{rms}^2 + \frac{1}{2}\frac{B_{rms}^2}{\mu_0}$

8. Card 8 of 20

   What is the momentum ($p$) transferred by an EM wave of energy $U$ to a perfectly absorbing surface?

   Hint: For a perfectly reflecting surface, it would be $2U/c$.

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   Answer

   $p = \frac{U}{c}$