Explanation

• A vector field with zero curl is called an irrotational field.
• Curl measures the tendency of rotation in a vector field.
• If curl = 0, there is no local rotation present.
• Such fields are derived from a scalar potential.

Last verified on 05-06-2026

Explanation

• The reciprocal lattice of a body-centered cubic (BCC) lattice is face-centered cubic (FCC).
• In crystallography, direct and reciprocal lattices are inversely related.
• FCC ↔ BCC are reciprocal to each other.
• Simple cubic (SC) is self-reciprocal.

Last verified on 05-06-2026

Explanation

• Einstein’s photoelectric equation explains energy conservation in photoelectric effect.
• Incident photon energy is used to overcome work function.
• Remaining energy becomes kinetic energy of emitted electron.
• Therefore, correct equation is hv = hv₀ + (1/2 mv²)max.
• Photoelectric effect was explained by Albert Einstein (1905).

Last verified on 05-06-2026

Explanation

• In gamma (γ) decay, only energy is released from the nucleus.
• The atomic number (Z) and mass number (A) do not change.
• The nucleus before and after decay remains the same element.
• Here, the product nucleus is Ni⁶⁵₂₈, so the parent nucleus is also Ni⁶⁵₂₈.

Last verified on 05-06-2026

Explanation

• Increasing the number of slits in a diffraction grating increases intensity.
• More slits means more waves interfere constructively at the central maximum.
• This results in stronger and sharper central bright fringe.
• Energy is concentrated more effectively in the main maxima.

Last verified on 05-06-2026

Explanation

• Driven harmonic oscillator is a system undergoing forced vibration.
• In forced vibrations, an external periodic force continuously acts on the system.
• The system oscillates with the frequency of the applied force.
• This differs from free oscillations, where no external force acts.

Last verified on 05-06-2026

Explanation

• He–Ne laser is a four-level laser system.
• It uses a mixture of helium and neon gases as the active medium.
• Four-level lasers are more efficient because population inversion is easier to achieve.
• Ruby laser is a three-level laser.

Last verified on 05-06-2026

Explanation

• The body cannot return to its original position when stress exceeds the elastic limit.
• Beyond the maximum elastic value, the material undergoes permanent deformation.
• Even after removing the stress, the original shape is not fully recovered.
• This behavior is called plastic deformation.

Last verified on 05-06-2026

Explanation

• The semi-major axis and the time period are related by Kepler's Third Law (Law of Periods).
• It states that the square of a planet's orbital period is proportional to the cube of its semi-major axis.
• Larger orbits take longer to complete.
• This law helps determine planetary distances and orbital periods.

Last verified on 05-06-2026

Explanation

1. ∂/∂x (x + 3y) = 1  
2. ∂/∂y (y - 2z) = 1  
3. ∂/∂z (x + mz) = m