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ISC Class 12 Wave Optics — practice questions

Explore 50 free Wave Optics questions in ISC Class 12 Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Wave Optics questions and exercises with answers

Showing questions 1–30 of 50.

Unpolarised light of intensity $I_0$ is passed through a single ideal polariser. The intensity of the transmitted light is:Read the answer and worked solution →Brewster's angle for a glass of refractive index $\sqrt{3}$ (relative to air) is:Read the answer and worked solution →Two point charges q₁ and q₂ separated by distance r in vacuum experience force F. If both charges are doubled AND the distance is halved, the new force is:Read the answer and worked solution →The SI unit of electric field is:Read the answer and worked solution →A dipole of moment p is placed in a uniform external field E. The torque on the dipole is:Read the answer and worked solution →A dipole of moment 10⁻²⁹ C·m is placed in a uniform field of 10⁵ N/C at angle 30°. The torque on the dipole is:Read the answer and worked solution →For a uniformly charged thin spherical shell of radius R and total charge Q, the electric field INSIDE the shell (r < R) is:Read the answer and worked solution →Linear charge density λ has SI units:Read the answer and worked solution →The Lorentz force on a charge q moving with velocity v in fields E and B is:Read the answer and worked solution →The force on a charge q moving with speed v perpendicular to a magnetic field B has magnitude:Read the answer and worked solution →The SI unit of electric charge is the:Read the answer and worked solution →Coulomb's law: force between two point charges is proportional to:Read the answer and worked solution →The value of k in Coulomb's law (in SI) is approximately:Read the answer and worked solution →Electric field strength at a point is defined as force per unit:Read the answer and worked solution →Total electric flux through a closed surface enclosing charge q (Gauss's law) is:Read the answer and worked solution →Electric field due to an INFINITE SHEET of charge with surface charge density σ:Read the answer and worked solution →Two point charges +2μC and -3μC are separated by 30 cm. The force on each (k = 9 × 10⁹):Read the answer and worked solution →Electric field due to a point charge q at distance r:Read the answer and worked solution →In SI units, the magnitude of the elementary charge e is approximatelyRead the answer and worked solution →Three point charges +1, −3, and +5 (in arbitrary units) are placed in a closed system. What is the total charge of the system?Read the answer and worked solution →The SI unit of magnetic flux is theRead the answer and worked solution →The current driven by an alternating voltage in a circuit is called:Read the answer and worked solution →The equivalent steady current giving the same average power loss is the:Read the answer and worked solution →Phase relationships between voltage and current in an ac circuit are shown using:Read the answer and worked solution →The quantity analogous to resistance for an inductor is called:Read the answer and worked solution →The opposition offered by a capacitor to alternating current is called:Read the answer and worked solution →What is the SI unit of inductive reactance?Read the answer and worked solution →In a purely resistive ac circuit, the voltage and the current are:Read the answer and worked solution →In a circuit containing an inductor, the current does what relative to the voltage?Read the answer and worked solution →In a circuit containing a capacitor, the current does what relative to the voltage?Read the answer and worked solution →

Worked practice questions

Unpolarised light of intensity $I_0$ is passed through a single ideal polariser. The intensity of the transmitted light is:

  1. $I_0$
  2. $I_0/2$
  3. $I_0\cos^2\theta$
  4. $I_0/4$
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Correct answer: B. $I_0/2$

Unpolarised light contains all polarisation directions with equal probability. Averaging Malus's law over all input angles gives $\langle I \rangle = I_0 \langle\cos^2\theta\rangle = I_0/2$. Once polarised, a second polariser would then attenuate further by $\cos^2\theta$ relative to its axis.

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Brewster's angle for a glass of refractive index $\sqrt{3}$ (relative to air) is:

  1. $30^\circ$
  2. $45^\circ$
  3. $60^\circ$
  4. $90^\circ$
Show answer and solution

Correct answer: C. $60^\circ$

**Brewster's law:** $\tan i_B = \mu$. With $\mu = \sqrt{3}$, $\tan i_B = \sqrt{3} \Rightarrow i_B = 60^\circ$. At this angle the reflected light is completely plane-polarised, with the electric field perpendicular to the plane of incidence.

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Two point charges q₁ and q₂ separated by distance r in vacuum experience force F. If both charges are doubled AND the distance is halved, the new force is:

  1. 4F
  2. 8F
  3. 16F
  4. 2F
Show answer and solution

Correct answer: C. 16F

F ∝ q₁q₂/r². **New:** F' ∝ (2q₁)(2q₂)/(r/2)² = 4 × 4 × F = **16F**. Each doubling of charge contributes factor 2 (so 4 total), halving distance contributes factor 4. 4 × 4 = 16.

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More Physics topics

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