List of top Physics Questions on Electromagnetic Waves

The frequency order of for \(γ-rays\ (b), X–rays\ (a), UV–rays\ (c)\):

The terminology of different parts of the electromagnetic spectrum is given in the text. Use the formula \(E = hν\) (for energy of a quantum of radiation: photon) and obtain the photon energy in units of eV for different parts of the electromagnetic spectrum. In what way are the different scales of photon energies that you obtain related to the sources of electromagnetic radiation?

Figure shows a capacitor made of two circular plates each of radius 12 cm, and separated by 5.0 cm. The capacitor is being charged by an external source (not shown in the figure). The charging current is constant and equal to 0.15 A.

1. Calculate the capacitance and the rate of charge of potential difference between the plates.
2. Obtain the displacement current across the plates.
3. Is Kirchhoff’s first rule (junction rule) valid at each plate of the capacitor? Explain.

Suppose that the electric field amplitude of an electromagnetic wave is \(E_0 = 120 \ N/C\) and that its frequency is \(ν = 50.0 \ MHz\). 

1. Determine, B0, ω, k, and λ. 
2. Find expressions for E and B.

In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of \(2.0 × 10^10 \ Hz\) and amplitude \(48\  V m^{−1}\). 

1. What is the wavelength of the wave?
2. What is the amplitude of the oscillating magnetic field?
3. Show that the average energy density of the E field equals the average energy density of the B field. \([c = 3 × 10^8 m s^{−1}]\)

The amplitude of the magnetic field part of a harmonic electromagnetic wave in vacuum is \(B_0 = 510\  nT\). What is the amplitude of the electric field part of the wave?

A charged particle oscillates about its mean equilibrium position with a frequency of \(10^9 Hz\). What is the frequency of the electromagnetic waves produced by the oscillator?

A radio can tune in to any station in the 7.5 MHz to 12 MHz band. What is the corresponding wavelength band?

A plane electromagnetic wave travels in vacuum along z-direction. What can you say about the directions of its electric and magnetic field vectors? If the frequency of the wave is 30 MHz, what is its wavelength?

A parallel plate capacitor made of circular plates each of radius R = 6.0 cm has a capacitance C = 100 pF. The capacitor is connected to a 230 V ac supply with a (angular) frequency of 300 rad s⁻¹.

1. What is the rms value of the conduction current?
2. Is the conduction current equal to the displacement current?
3. Determine the amplitude of B at a point 3.0 cm from the axis between the plates.