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Practice each question, then open the answer or worked solution.
A charged particle oscillates about its mean equilibrium position with a frequency of 109 Hz. The electromagnetic waves produced:
a) will have a frequency of 109 Hz
b) will have a frequency of 2 × 109 Hz
c) will have a wavelength of 0.3 m
d) fall in the region of radiowaves
a) will have a frequency of 109 Hz
c) will have a wavelength of 0.3 m
d) fall in the region of radiowaves
The source of electromagnetic waves can be a charge
a) moving with a constant velocity
b) moving in a circular orbit
c) at rest
d) falling in an electric field
b) moving in a circular orbit
d) falling in an electric field
An EM wave of intensity I falls on a surface kept in vacuum and exerts radiation pressure p on it. Which of the following are true?
a) radiation pressure is I/c if the wave is totally absorbed
c) radiation pressure is 2I/c if the wave is totally reflected
d) radiation pressure is in the range I/c < p < 2I/c for real surface
Very Short AnswersWhy is the orientation of the portable radio with respect to broadcasting station important?
The orientation of the portable radio with respect to the broadcasting station is important because the electromagnetic waves are plane polarised and the antenna should be placed parallel to the vibration of the electric or magnetic field of the wave.
Why does a microwave oven heats up a food item containing water molecules most efficiently?
The microwave oven heats up a food item containing water molecule most efficiently because the frequency of the microwave and the resonant frequency of the water molecules are the same.
The charge on a parallel plate capacitor varies as q = q0 cos 2πvt. The plates are very large and close together. Neglecting the edge effects, find the displacement current through the capacitor?
The displacement current through the capacitor is Id = Ic = dq/dt
Given, q = q0 cos 2πvt
Substituting the values, we get
Id = Ic = -2πvq0 sin 2π vt
A variable frequency a.c source is connected to a capacitor. How will the displacement current change with a decrease in frequency?
Capacitive reaction Xc = 1/2πfc
As there is a decrease in frequency, Xc increases and the conduction current becomes inversely proportional to Xc.
The magnetic field of a beam emerging from a filter facing a floodlight is given by B0 = 12 × 10-8 sin (1.20 × 107z – 3.60 × 1015 t)T. What is the average intensity of the beam?
B0 = 12 × 10-8 sin (1.20 × 107z – 3.60 × 1015 t)T
B0 = 12 × 10-8 T
Iav = 1.71 W/m2
Poynting vectors S is defined as a vector whose magnitude is equal to the wave intensity and whose direction is along the direction of wave propagation. Mathematically, it is given by S = 1/μ0 E × B. Show that nature of S versus t graph.
Professor C.V.Raman surprised his students by suspending freely a ting light ball in a transparent vacuum chamber by shining a laser beam on it. Which property of EM waves was he exhibiting? Give one more example of this property.
The radiation pressure property of EM waves was exhibited by Professor CV Raman.
Short Answers