EM Waves important questions

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Hello, readers 😊! Here you will learn the most important questions from Chapter EM Waves for Class 12th. It includes topics like conduction current, displacement current, Maxwell’s Equations, Hertz’s experiment, and properties of Electromagnetic Waves. EM Waves important questions

EM Waves important questions

Why is the orientation of the portable radio with respect to the broadcasting station important?

Answer: Radio signals transmitted from broadcast stations are in the form of plane-polarized electromagnetic waves (radio waves). These waves are received by radio if the receiving antenna is parallel to either the electric field or magnetic field of the wave.

Why does a microwave oven heat up a food item containing water molecules most efficiently?

Answer: In a microwave oven, the frequency of the microwaves is matched with the resonant frequency of the water molecules so that energy from the waves is efficiently transferred to the kinetic energy of the molecules. Thus, due to the increase in kinetic energy of water molecules, the temperature of the food containing water increases.

Every EM wave has certain frequency. Name two parameters of an em wave that oscillate with this frequency.

Ans: Electric field vector and Magnetic field vector.

What is the phase difference between electric and magnetic field vectors in an em wave?

Ans: π / 2 is the phase difference between electric and magnetic field vectors in an em wave.

Name em radiations used for detecting fake currency notes.

Ans: U.V. Radiation.

Give any two uses of microwaves.

Ans: Radar, Microwave ovens

Name the phenomenon which justifies the transverse nature of em waves.

Ans: Polarization.

Arrange the following em waves in descending order of wavelengths :gamma-ray, microwaves UV radiations.

Ans: Microwave, U V radiation, gamma-rays.

Which component E or B of an em wave is responsible for visible effect?

Ans: E

Write expression for speed of em waves in a medium of electrical permittivity and magnetic permeability .

Ans: speed of wave

Which of the following has longest penetration power?
UV radiation, X-ray, Microwaves.

Ans: X-rays has longest penetration power.

Which of the following has least frequency ?
IR radiations, visible radiation, radio waves.

Ans: Radio-waves has least frequency.

Which physical quantity is the same for microwaves of wavelength 1mm and UV radiations of 1600 A° in vacuum?

Ans: Speed is same for EM waves in a medium.

Name two physical quantities which are imparted by an em wave to a surface on which it falls.

Ans: Energy and pressure.

EM Waves Test Paper

Time: 1:00 hr                      Class-XII     PHYSICS (Theory )- 042                       Max. Marks: 25

General Instruction

1. All questions are compulsory
2. There is no choice.     

1. What are the basic sources of E and B?                              (1)
2. Name the electromagnetic radiation which can be produced by a klystron or a magnetron valve.  (1)
3. Name the electromagnetic waves used for detecting fake currency notes. (1)
4. Draw a sketch of a plane electromagnetic wave propagating along the z-direction. Depict clearly the directions of electric and magnetic fields varying sinusoidally with z.    (1)
5. Name the phenomenon which justifies transverse nature of electromagnetic waves. (1)
6. Ajay’s father purchased a microwave oven. The mother of Ajay put vegetables in a metallic container for cooking in the microwave oven. Ajay asked her mother not to put vegetables in the metallic container. She must put vegetables in a non metallic container for cooking in the microwave oven. Now answer the following questions. 
   • (a)  How microwave heat food?
   • (b) Comment on the attitude of Ajay.  (2)
7. Calculate the electric and magnetic fields produced by the radiation coming from a 100 W bulb at a distance of 3 m. Assume that the efficiency of the bulb is 2.5% and it is a point source. (2)
8. In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of 3.0 x 10¹¹Hz and amplitude 50Vm^-1. (a)What is the wavelength of the wave? (b)What is the amplitude of the oscillating magnetic field? (2)
9. Identify the following electromagnetic radiations as per the wavelengths given below. Write one application of each. (a)10^-3nm (b)10^-3m.                                     (2)
10. Show that the average energy density of electric field is equal to the average energy density of the magnetic field.          (03)
11. A capacitor of capacitance ‘C’ is being charged by connecting it across a dc source along with an ammeter. Will the ammeter show a momentary deflection during the process of charging? If so, how would you explain this momentary deflection and the resulting continuity of current in the circuit? Write the expression for the current inside the capacitor.  (3)
12. Draw a labeled diagram of Hertz’s experiment. Explain how electromagnetic radiations are produced using this set–up. (3)
13. The electric field of a plane electromagnetic wave in vacuum is represented by E_x = 0, E_y = 0.5 cos [2π x 10⁸(t – x/c)],   E_z = 0   (a) What is the direction of propagation of electromagnetic wave? (b)Determine the wavelength of the wave. (c)Calculate the component of associated magnetic field.  (3)

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