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Karnataka PUC II Electromagnetic Waves — practice questions

Explore 116 free Electromagnetic Waves questions in Karnataka PUC II 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 116.

Two thin lenses of focal lengths $+10$ cm and $+20$ cm are placed in contact. The power of the combination, in diopters, is:Read the answer and worked solution →Two light sources can produce sustained interference fringes on a screen only if they are:Read the answer and worked solution →Faraday's law of electromagnetic induction (in its quantitative form, with sign) is:Read the answer and worked solution →Lenz's law is a manifestation of which fundamental conservation principle?Read the answer and worked solution →The SI unit of magnetic flux is:Read the answer and worked solution →The SI unit of self-inductance $L$ is:Read the answer and worked solution →The induced EMF in a coil due to changing current in itself is given by:Read the answer and worked solution →The energy stored in an inductor of inductance $L$ carrying current $I$ is:Read the answer and worked solution →Mutual inductance $M$ between two coils satisfies:Read the answer and worked solution →The energy density (energy per unit volume) of a magnetic field $B$ in free space is:Read the answer and worked solution →A conducting rod of length 1 m moves with velocity 5 m/s perpendicular to a uniform magnetic field of 0.4 T. The motional EMF is:Read the answer and worked solution →**Huygens' principle** states that every point on a wavefront acts as a:Read the answer and worked solution →Which of the following phenomena conclusively proves that **light is a transverse wave**?Read the answer and worked solution →The **wavelength** of light of wavelength 600 nm in air becomes (in water, n = 1.33) approximately:Read the answer and worked solution →When unpolarized light passes through a single ideal polarizer, the transmitted intensity is:Read the answer and worked solution →**Malus' law** gives the transmitted intensity through a second polarizer as:Read the answer and worked solution →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 →

Worked practice questions

Two thin lenses of focal lengths $+10$ cm and $+20$ cm are placed in contact. The power of the combination, in diopters, is:

  1. $5$ D
  2. $10$ D
  3. $15$ D
  4. $20$ D
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Correct answer: C. $15$ D

**For thin lenses in contact**, powers add: $P = P_1 + P_2$. $P_1 = \dfrac{1}{f_1\text{ (m)}} = \dfrac{1}{0.10} = 10$ D. $P_2 = \dfrac{1}{0.20} = 5$ D. $P_{\text{total}} = 10 + 5 = 15$ D. Equivalently, $\dfrac{1}{F} = \dfrac{1}{10} + \dfrac{1}{20} = \dfrac{3}{20}$ giving $F = \dfrac{20}{3}$ cm $\approx 6.67$ cm so $P = \dfrac{100}{6.67} = 15$ D.

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Two light sources can produce sustained interference fringes on a screen only if they are:

  1. Coherent (constant phase difference)
  2. Of identical intensity
  3. From the same physical lamp
  4. Polarised in the same direction
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Correct answer: A. Coherent (constant phase difference)

Sustained interference needs sources with a constant phase relationship over time, which is what coherence means. Two ordinary lamps emit light with phases that vary randomly at $10^{-8}$ s scale so their interference pattern washes out almost instantly. The two slits in Young's experiment achieve coherence because both are illuminated by the same primary source, inheriting its phase. Equal intensity (B) improves fringe contrast but is not required. Same lamp (C) is one way to ensure coherence but not the only way (e.g. laser pairs). Polarisation alignment (D) matters for contrast, not for the existence of fringes.

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Faraday's law of electromagnetic induction (in its quantitative form, with sign) is:

  1. $e = \phi / t$
  2. $e = \phi \cdot dt$
  3. $e = -d\phi/dt$
  4. $e = +d\phi/dt$
Show answer and solution

Correct answer: C. $e = -d\phi/dt$

The induced EMF equals the **negative** rate of change of magnetic flux through the circuit: $e = -d\phi/dt$. The minus sign embeds Lenz's law — direction of induced EMF opposes the flux change.

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More Physics topics

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