NEET Physics: Electromagnetic Waves — Practice Set 3

Q1. Why does the speed of electromagnetic waves in vacuum remain constant irrespective of their source’s motion?

A. It depends only on universal constants
B. It varies with the source’s velocity
C. It depends on the medium’s density
D. It is influenced by frequency

Q2. Why are ultraviolet lamps used in water purifiers?

A. To heat the water
B. To enhance taste
C. To kill germs
D. To emit visible light

Q3. Which frequency range corresponds to the ultrahigh frequency (UHF) band used by cellular phones?

A. \( 88 \, \text{MHz} \) to \( 108 \, \text{MHz} \)
B. \( 530 \, \text{kHz} \) to \( 1710 \, \text{kHz} \)
C. Within \( 500 \, \text{kHz} \) to \( 1000 \, \text{MHz} \)
D. \( 4 \times 10^{14} \, \text{Hz} \) to \( 7 \times 10^{14} \, \text{Hz} \)

Q4. Why do X-rays require careful handling in medical applications?

A. Low energy absorption
B. Visible light emission
C. Potential tissue damage
D. Thermal heating

Q5. What is the typical wavelength range of X-rays as per the document?

A. \( > 0.1 \, \text{m} \)
B. \( 10^{-8} \, \text{m} \) to \( 10^{-13} \, \text{m} \)
C. \( 1 \, \text{mm} \) to \( 700 \, \text{nm} \)
D. \( 400 \, \text{nm} \) to \( 0.6 \, \text{nm} \)

Q6. An electromagnetic wave has a wave number \( k = 3 \, \text{rad/m} \). What is its wavelength in vacuum?

A. 1.05 m
B. 2.09 m
C. 3.14 m
D. 4.18 m

Q7. What did Maxwell's unification of electricity, magnetism, and light lead to?

A. Understanding light as an electromagnetic wave
B. Discovery of magnetic monopoles
C. Elimination of electromagnetic waves
D. Proof that light requires a medium

Q8. What enables electromagnetic waves to propagate through vacuum?

A. Presence of charged particles
B. High frequency of oscillation
C. Constant wavelength
D. Self-sustaining electric and magnetic fields

Q9. A capacitor in a circuit has a rate of change of electric flux of \( 4 \times 10^{11} \, \text{Vm/s} \). What is the displacement current? (Given \( \varepsilon_0 = 8.85 \times 10^{-12} \, \text{F/m} \))

A. 3.54 A
B. 1.77 A
C. 7.08 A
D. 8.85 A

Q10. According to Maxwell's equations, what is the speed of electromagnetic waves in a medium with permittivity \( \varepsilon \) and permeability \( \mu \)?

A. \( v = \frac{1}{\sqrt{\mu \varepsilon}} \)
B. \( v = \sqrt{\mu \varepsilon} \)
C. \( v = \frac{\mu}{\varepsilon} \)
D. \( v = \frac{1}{\mu \varepsilon} \)

Q11. An electromagnetic wave in vacuum has an electric field amplitude of \( 30 \, \text{V/m} \). What is the magnetic field amplitude? (Given \( c = 3 \times 10^8 \, \text{m/s} \))

A. \( 0.5 \times 10^{-7} \, \text{T} \)
B. \( 0.75 \times 10^{-7} \, \text{T} \)
C. \( 0.9 \times 10^{-7} \, \text{T} \)
D. \( 1 \times 10^{-7} \, \text{T} \)

Q12. What is the approximate wavelength range of microwaves as per the document?

A. \( > 0.1 \, \text{m} \)
B. \( 0.1 \, \text{m} \) to \( 1 \, \text{mm} \)
C. \( 1 \, \text{mm} \) to \( 700 \, \text{nm} \)
D. \( 400 \, \text{nm} \) to \( 0.6 \, \text{nm} \)

Q13. An electromagnetic wave propagates in the \( z \)-direction with electric field along the \( x \)-axis. In which direction is the magnetic field oriented?

A. \( x \)-axis
B. \( y \)-axis
C. \( z \)-axis
D. None of these

Q14. What insight does the Ampere-Maxwell law provide about the symmetry of electromagnetic fields?

A. Symmetry in field induction
B. Asymmetry due to charges
C. Elimination of magnetic fields
D. Static field dominance

Q15. What precaution must be taken when using X-rays in medical applications?

A. Use them only in vacuum
B. Increase exposure time
C. Use them without shielding
D. Avoid unnecessary or overexposure

Physics — Electromagnetic Waves

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Why does the speed of electromagnetic waves in vacuum remain constant irrespective of their source’s motion?

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