Q21 of 26 Page 1

Arrange the following electromagnetic waves in the order of their increasing wavelength:

(a) γ-rays


(b) Microwaves


(c) X-rays


(d) Radio waves


How are infra-red waves produced? What role does infra-red radiation play in (i) maintaining the Earth’s warmth and (ii) physical therapy?


The ranges of electromagnetic waves are given as:


(a) γ-rays = <10ˉ � nm


(b)Microwaves = 0.1 m to 1 mm


(c) x-rays = 1 nm to 10ˉ � nm


(d) Radio waves = >0.1 m


Following is the arrangement of electromagnetic wave in the increasing order of their wavelength:


a) Gamma rays


b) X-rays


c) Micro waves


d) Radio waves


i) When sun light falls on the Earth’s atmosphere, its major part is reflected back in the space. After multiple reflections, the infrared radiations of sunlight are absorbed by the atmosphere because they do not have enough energy to go out of earth’s atmosphere. Infrared radiations have hot radiations so after multiple reflection, they heat up the atmosphere and hence they keep the surface of Earth warm.


ii) In physical therapy the warmth and heat energy of infrared radiations are used. These radiations provide soothing effect in our muscles. They repair and heal up the weak cells and tissues of out body.


More from this chapter

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19

Write symbolically the nuclear+decay process of C116. Is the decayed product X an isotope or isobar of ?Given the mass values m ( ) = 11.011434 u and m (X) = 11.009305 u. Estimate the Q-value in this process.

20

An object is placed 15 cm in front of a convex lens of focal length 10 cm. Find the nature and position of the image formed. Where should a concave mirror of radius of curvature 20 cm be placed so that the final image is formed at the position of the object itself?

22

Explain briefly the process of charging a parallel plate capacitor when it is connected across a d.c. battery.

A capacitor of capacitance ‘C’ is charged to ‘V’ volts by a battery. After some time, the battery is disconnected and the distance between the plates is doubled. Now a slab of dielectric constant, 1 < k < 2, is introduced to fill the space between the plates. How will the following be affected: (a) The electric field between the plates of the capacitor


(b) The energy stored in the capacitor


Justify your answer by writing the necessary expressions.


23

Ajit had a high-tension tower erected on his farm land. He kept complaining to the authorities to remove it as it was occupying a large portion of his land. His uncle, who was a teacher, explained to him the need for erecting these towers for efficient transmission of power. As Ajit realized its significance, he stopped complaining. Answer the following questions:

(a) Why is it necessary to transport power at high voltage?


(b) A low power factor implies large power loss. Explain.


(c) Write two values each displayed by Ajit and his uncle.