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ISC Class 12 Electromagnetic Waves — practice questions

Explore 52 free Electromagnetic Waves questions in ISC Class 12 Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Electromagnetic Waves questions and exercises with answers

Showing questions 1–30 of 52.

Quantisation of electric charge means:Read the answer and worked solution →A charge of −12 nC is given to a body. The number of excess electrons on the body is:Read the answer and worked solution →Coulomb's law in vacuum is F = (1/4πε₀)(q₁q₂/r²). The value of 1/4πε₀ is approximately:Read the answer and worked solution →A charged particle moving perpendicular to a uniform magnetic field follows aRead the answer and worked solution →The magnetic field at the centre of a circular loop of radius R carrying current I isRead the answer and worked solution →Inside an ideal infinite solenoid with n turns per unit length carrying current I, the magnetic field isRead the answer and worked solution →The magnetic field at distance r from a long straight wire carrying current I isRead the answer and worked solution →Magnetic field lines around a bar magnetRead the answer and worked solution →The potential energy of a magnetic dipole in an external uniform field B isRead the answer and worked solution →Gauss's law for magnetism states that the net magnetic flux through ANY closed surface isRead the answer and worked solution →A magnetic needle is in stable equilibrium when its magnetic moment m isRead the answer and worked solution →The pole strength of a magnet has SI unitRead the answer and worked solution →The work required to rotate a magnetic dipole of moment m in a field B from θ = 0 to θ = 180° isRead the answer and worked solution →Which of the following is INCORRECT about magnetic field lines?Read the answer and worked solution →The magnetic moment vector m of a bar magnet pointsRead the answer and worked solution →Lenz's law is a direct consequence ofRead the answer and worked solution →Self-inductance of a long solenoid of length l, cross-section A, with n turns per unit length isRead the answer and worked solution →Order by Wavelength: EM Spectrum (ISC 12)Read the answer and worked solution →Which band is used as a diagnostic tool in medicine?Read the answer and worked solution →Compared with visible light, infrared waves have frequencies that are:Read the answer and worked solution →Who first demonstrated electromagnetic waves experimentally?Read the answer and worked solution →Sort the radiation by sourceRead the answer and worked solution →NEET · Physics · EM Spectrum — Order by FrequencyRead the answer and worked solution →Order the spectrum by frequencyRead the answer and worked solution →The speed of an EM wave in vacuum equals:Read the answer and worked solution →Electromagnetic waves are produced by charges that are:Read the answer and worked solution →Infrared waves are also referred to as:Read the answer and worked solution →Radar systems used in aircraft navigation use:Read the answer and worked solution →Most ultraviolet radiation from the Sun is absorbed in the:Read the answer and worked solution →In an electromagnetic wave, E and B are:Read the answer and worked solution →

Worked practice questions

Quantisation of electric charge means:

  1. Charge can take any continuous value
  2. All free charges are integral multiples of the elementary charge e (1.602 × 10⁻¹⁹ C)
  3. Only positive charges are quantised
  4. Charge is always zero
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Correct answer: B. All free charges are integral multiples of the elementary charge e (1.602 × 10⁻¹⁹ C)

**Quantisation of charge**: q = ne, where n is an integer (positive or negative) and e = 1.602 × 10⁻¹⁹ C (charge on proton; electron has -e). At macroscopic scales (1 μC ≈ 6 × 10¹² electrons) quantisation is unobservable matters only at microscopic level.

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A charge of −12 nC is given to a body. The number of excess electrons on the body is:

  1. 7.5 × 10¹⁰
  2. 1.92 × 10⁻²⁷
  3. 7.5 × 10¹⁹
  4. 1.92 × 10¹⁰
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Correct answer: A. 7.5 × 10¹⁰

n = |q|/e = (12 × 10⁻⁹) / (1.6 × 10⁻¹⁹) = **7.5 × 10¹⁰ electrons**. Body is negatively charged → excess electrons (matches the −12 nC sign).

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Coulomb's law in vacuum is F = (1/4πε₀)(q₁q₂/r²). The value of 1/4πε₀ is approximately:

  1. 8.85 × 10⁻¹² N m² C⁻²
  2. 9 × 10⁹ N m² C⁻²
  3. 1.6 × 10⁻¹⁹ N m² C⁻²
  4. 6.022 × 10²³
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Correct answer: B. 9 × 10⁹ N m² C⁻²

**k = 1/(4πε₀) ≈ 9 × 10⁹ N m²/C²** (in vacuum). ε₀ = 8.854 × 10⁻¹² C²/(N m²) is the permittivity of free space. In a medium, replace ε₀ by ε = ε₀ × ε_r (relative permittivity / dielectric constant).

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More Physics topics

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