Chapter 8: Electromagnetic waves
Important Questions
1. Name the electromagnetic radiation’s used for(a) water purification, and(b)eye surgery.
2. How are infrared waves produced? Why are these referred to as ‘heat waves’? Write their one important use.
3. How does a charge q oscillating at certain frequency produce electromagnetic waves? Sketch a schematic diagram depicting electric and magnetic fields for an electromagnetic wave propagating along the Z-direction.
4. (a) Why are infra-red waves often called heat waves? Explain.
(b) What do you understand by the statement, “Electromagnetic waves transport momentum”?
5. Answer the following:
(a) Name the em waves which are used for the treatment of certain forms of cancer. Write their frequency range.
(b) Welders wear special glass goggles while working. Why? Explain.
(c) Why infrared waves are often called as heat waves? Give their one application.
Sample Questions
1. Answer the following:
(a) Name the em waves which are suitable for radar systems used in aircraft navigation. Write the range of frequency of these waves.
(b) If the earth did not have atmosphere, would its average surface temperature be higher or lower than what it is now? Explain.
(c) An em wave exerts pressure on the surface on which it is incident. Justify.
2. Define the terms “stopping potential’ and ‘threshold frequency’ in relation to photoelectric effect. How does one determine these physical quantities using Einstein’s equation?
3. How are electromagnetic waves produced? What is the source of the energy carried by a propagating electromagnetic wave? Identify the electromagnetic radiations used
(i) In remote switches of household electronic device; and
(ii) as diagnostic tool in medicine
4. How are e.m. waves produced by oscillating charges?
Draw a sketch of linearly polarized e.m. waves propagating in the Z-direction. Indicate the directions of the oscillating electric and magnetic fields.
OR
Write Maxwell’s generalization of Ampere’s Circuital Law. Show that in the process of charging a capacitor, the current produced within the plates of the capacitor is 
where φE is the electric flux produced during charging of the capacitor plates.
5. State two important properties of photon which are used to write Einstein’s photoelectric equation. Define
(i) Stopping potential and
(ii) Threshold frequency, using Einstein’s equation and drawing necessary plot between relevant quantities.