Important questions of electromagnetic waves

    Questions on ELECTROMAGNETIC WAVES 

                    Chapter- 8  class 12 Physics 

Q.1 Green light of mercury has a wavelength 5.5 x 10^ -5 cm a) what is the frequency in MHz and period in microsecond in vacuum? b) what is the wavelength in glass if refractive index of glass is 1.5. Given, c = 3×10^ 8 m/s.                     Ans.  5.5 x10^8 MHz , 1.8 x 10^-9 Microseconds, 3.6 x10^-7 m

Q.2 Electromagnetic waves travel in a medium with a speed of 2×10^8 m/s. The relative permeability of medium is 1.Find the relative permittivity.                 Ans. 2.25

Q.3 The magnetic field in a plane electromagnetic wave is given by By= 2x10^-7 sin [ 0.5 x10^3X + 1.5 x10^11 t] T. A) What is the wavelength and frequency of the wave? B) write an expression for the electric field.                  Ans. 1.257 x10^-2m, 2.387 x 10^10 Hz and Ez= 60 sin [ 0.5 x10^3X + 1.5 x10^11 t] V/m 

Q.4 The electric field of a plane electromagnetic wave in vacuum is represented by Ex= 0, Ey= 0.5 cos[2 π x10^8(t- x/c) and Ez= 0 a) What is the direction of propagation of electromagnetic waves? b) determine the wavelength of the wave c) compute the component of associated magnetic field.        Ans.  Positive x direction, 3m, Bz= 0.5/3x 10^8 cos[2 π x10^8(t- x/c) 

Q.5 A plane electromagnetic wave propagating in the X direction has a wavelength of 6 mm. The electric field is in the Y-direction and its maximum magnitude is 33 V per metre. Write suitable equations for the electric and magnetic fields as a function of x and t.                 Ans. Ey= 33 sin π x 10^11 (t-x/c) and Bz= 1.1 x10^-7 sin π x10^11(t-x/c)

Q.6 Light with the energy flux of 18 Webber per centimetre square falls on a non-reflecting surface at normal incidence. If the surface has an area of 20 cm², find the average force exerted on the surface during a 30 minutes time span.         Ans. 1.2 x 10^-6 N 

Q.7 Find the amplitude of the electric field in a parallel beam of light of intensity eight Webber per m².                Ans. 77.6 N/C 

Q.8 Arrange the following electromagnetic radiations in the ascending order of their frequencies microwave, radiowave, x-rays, Gamma rays

Q.9 Name the part of electromagnetic spectrum whose wavelength lies in the range of 10^-10 m give its two uses. 

Q.10 In what way are the directions of the electric and magnetic field vectors representing an electromagnetic wave related to each other. 

Q.11 Arrange the given electromagnetic radiations in the descending order of the frequencies infrared, x-rays, ultraviolet and gamma rays

Q.12 How does the frequency of a beam of ultraviolet light change, when it goes from air into glass. 

Q.13 Which part of electromagnetic spectrum has largest penetrating power? 

Q.14 Identify the part of the electromagnetic spectrum, which is :- i) suitable for radar system used in aircraft navigation. ii) adjacent to the low-frequency end of the electromagnetic spectrum. iii) produced in nuclear reaction. iv) produced by bombarding a metal target by high speed electron

Q.15 Find the wavelength of electro magnetic waves of frequency 6×10^12 Hz in free space. Give its two applications. 

Q.16 The oscillating magnetic field in a plane electromagnetic wave is given by, By= 8x 10^-6 sin [2 x 10^11 t + 300 π x] T a) Calculate the wavelength of the wave? b) Write down the expression for the oscillating electric field.