Dual Nature of Electromagnetic Radiation - UNSOLVED PRACTICE SET

Q7. What is electromagnetic radiation? Name four types of electromagnetic radiation in order of increasing wavelength.

Q8. Write the mathematical relationship between wavelength, frequency, and speed of electromagnetic waves. What are the units of each quantity? 

Q9. What is the electromagnetic spectrum? Arrange the following in order of increasing energy: microwaves, X-rays, infrared, visible light.

Q10. How did the wave theory of light fail to explain black body radiation and the photoelectric effect?

Q11. Your mobile phone uses radio waves to connect to the tower, your TV remote uses infrared, and your doctor uses X-rays to check for fractures. All three are electromagnetic waves but have very different effects. Explain why X-rays can pass through flesh but radio waves cannot, based on their wavelength and energy.

Q12. What is a photon? How does the energy of a photon relate to the frequency of radiation?

Q13. Explain the wave nature of electromagnetic radiation. Describe the characteristics of a wave — wavelength, frequency, wave number, and velocity. Draw a diagram showing an electromagnetic wave and label its components. How does the energy of electromagnetic radiation vary across the electromagnetic spectrum?

Q14. Describe the experimental observations that led to the conclusion that electromagnetic radiation has a dual nature — both wave-like and particle-like. Explain:

(a) How the photoelectric effect supports the particle nature of light

(b) How diffraction and interference support the wave nature of light

(c) Why neither wave theory nor particle theory alone can explain all phenomena

What is the significance of Planck's quantum theory in resolving this duality?

Q15. During a school trip to a science museum, you see an exhibit on the electromagnetic spectrum.

(a) The exhibit shows that sunlight reaching Earth contains UV, visible, and infrared radiation. Why does the ozone layer block most UV radiation but not visible light? (Hint: Think about energy and wavelength)

(b) A solar panel on display converts sunlight into electricity. Would it work better with infrared or visible light? Explain using the photon energy equation E = hν.

(c) Your microwave oven at home uses microwaves to heat food. Why don't microwaves escape through the metal mesh on the door? (Hint: Consider wavelength and mesh size)

(d) A doctor's X-ray machine has a warning sign: "Radiation hazard." Why are X-rays more dangerous than radio waves, even though both are electromagnetic waves?

Q16. A radio station broadcasts at a frequency of 100 MHz.

(a) Calculate the wavelength of these radio waves.

(b) Calculate the energy of one photon of this radiation. (Planck's constant h = 6.626 × 10⁻³⁴ J·s)

(c) Compare this energy with the energy of a photon of visible light (λ = 500 nm). Which has higher energy and by what factor?

(Speed of light c = 3 × 10⁸ m/s)

Q17. The wavelength of red light is approximately 700 nm and that of violet light is 400 nm.

(a) Calculate the frequency of red light and violet light.

(b) Calculate the energy of one photon of each colour.

(c) A photosensitive material requires photons with energy at least 3.0 × 10⁻¹⁹ J to eject electrons. Which colour light — red or violet — can cause the photoelectric effect in this material? Show your calculation.

(Planck's constant h = 6.626 × 10⁻³⁴ J·s, c = 3 × 10⁸ m/s)

Q18. A sodium street lamp emits yellow light of wavelength 589 nm.

(a) Calculate the frequency of this yellow light.

(b) Calculate the energy of one mole of photons of this yellow light.

(c) If the lamp consumes 100 W of power and is 20% efficient at converting electrical energy to light, how many photons does it emit per second?

(d) Why do sodium lamps give a characteristic yellow colour and not white light?

(Planck's constant h = 6.626 × 10⁻³⁴ J·s, c = 3 × 10⁸ m/s, Avogadro's number = 6.022 × 10²³ mol⁻¹)