Physics Questions and Answers

PHYSICS- VERY SHORT QUESTIONS [1 MARKS] What is simple harmonic motion and its various types? Simple harmonic motion is a periodic motion where acceleration is proportional to displacement and directed toward the mean position. Types: Linear SHM and Angular SHM. A wave of frequency 30Khz travelling through water with the speed of 300 m/s. What will be its wavelength? Wavelength = 𝜆 = 𝑣 𝑓 = 300 30 , 000 = 0.01   m λ= f v ​ = 30,000 300 ​ =0.01m. Sound is longitudinal wave whereas light is transverse wave, why? Sound oscillates parallel to wave propagation; light oscillates perpendicular to it. Name any three phenomena that explain the wave nature of light. Diffraction, interference, polarization. What is the basic phenomenon behind laser emission? Stimulated emission of radiation. What would be the path difference between two waves to produce constructive interference? Path difference = 𝑛 𝜆 nλ (where 𝑛 n is an integer). State necessary conditions for diffraction to occur. The obstacle/aperture size should be comparable to the wavelength of the wave. What is an electric dipole? A pair of equal and opposite charges separated by a small distance. What do you understand by the curl of an electrostatics field? Curl of an electrostatic field is zero because it is conservative. What are ferromagnetic materials? Give some examples. Materials with strong magnetic properties (e.g., iron, cobalt, nickel). What does hysteresis curve for magnetic materials represent? It represents the relationship between magnetic flux density and magnetizing force, showing energy loss. What is the electric displacement? Write mathematical expression for it. Electric displacement: 𝐷 = 𝜀 0 𝐸 + 𝑃 D=ε 0 ​ E+P. Name the phenomenon when a sound wave passes from air into water and changes its direction. Refraction. A sound wave of frequency 3500 Hz travelling through water with speed 350 m/s. What will be its wavelength? Wavelength = 𝜆 = 𝑣 𝑓 = 350 3500 = 0.1   m λ= f v ​ = 3500 350 ​ =0.1m. Transverse waves are not found in liquid and gases. Why? They lack shear elasticity. State Huygens principle of propagation of light. Every point on a wavefront acts as a source of secondary wavelets. What do you understand by diffraction of light? Bending of light around obstacles or edges of slits. What is the stimulated emission of light in laser? Emission of photons triggered by incident photons of the same energy. What do you understand by the curl and divergence of an electrostatic field? Curl is zero; divergence relates to charge density ( ∇ ⋅ 𝐸 = 𝜌 𝜀 0 ∇⋅E= ε 0 ​ ρ ​ ). What is electric dipole moment? It is 𝑝 = 𝑞 𝑑 p=qd, the product of charge and separation distance. What are bound charges? Charges bound to atoms/molecules in a dielectric material. What do you mean by periodic motion and SHM? Periodic motion repeats after regular intervals; SHM is a special periodic motion with restoring force proportional to displacement. Define force constant of a spring and its dimensions. Force constant 𝑘 = Force displacement k= displacement Force ​ ; dimensions: M L T − 2 MLT −2 . How Fresnel diffraction differs from Fraunhofer diffraction? Fresnel: Near-field diffraction. Fraunhofer: Far-field diffraction. Name the scientist who gave us the theory of laser emission. Albert Einstein. What do you mean by superposition principle of two waves? The net displacement is the vector sum of individual wave displacements. Write the Clausius-Mossotti equation of dielectric material. 𝜀 𝑟 − 1 𝜀 𝑟 + 2 = 𝑁 𝛼 3 𝜀 0 ε r ​ +2 ε r ​ −1 ​ = 3ε 0 ​ Nα ​ . What are polar and non-polar molecules? Polar molecules: Have a permanent dipole (e.g., H 2 2 ​ O). Non-polar: No permanent dipole (e.g., O 2 2 ​ ). What is electrostatic potential and its SI unit? Work done per unit charge; SI unit: Volt (V). What is Curie temperature in a magnetic material? The temperature above which a material loses ferromagnetic properties. What is displacement current? Displacement current: 𝐼 𝑑 = 𝜀 0 𝑑 Φ 𝐸 𝑑 𝑡 I d ​ =ε 0 ​ dt dΦ E ​ ​ . What is the SI unit of magnetic susceptibility? It is dimensionless (no unit). Why two independent sources of light of the same wavelength cannot produce observable interference patterns? Due to lack of coherence. What are Rayleigh criteria for the limit of resolution? Minimum angular separation at which two objects are resolvable. What are the main characteristics of a laser beam? Coherence, monochromaticity, directionality, intensity. What is the physical significance of grad( 𝜙 𝐸 ϕ E ​ )? It represents the electric field intensity. What is Kepler’s law of planetary motion? Planets move in elliptical orbits with the Sun at one focus. Comment on the statement “Earth can be taken as an inertial frame of reference.” Approximate due to negligible rotation and acceleration effects. What is phasor representation of SHM? Circular motion projection on a line. The frequency of SHM is 100 Hz. Calculate time for it. Time period = 𝑇 = 1 𝑓 = 1 100 = 0.01   s T= f 1 ​ = 100 1 ​ =0.01s. Define the terms Eigen frequency and eigenfunction. Eigenfrequency: Natural vibration frequency. Eigenfunction: Associated wavefunction. How does the dispersive medium differ from the non-dispersive medium? Dispersive: Speed depends on frequency. Non-dispersive: Independent of frequency. Why two levels of laser do not exist? Population inversion cannot occur. What is the value of potential on equipotential surfaces? Constant. What is the physical significance of ∇ ⋅ 𝐵 = 0 ∇⋅B=0? No magnetic monopoles exist. Write the mathematical expression for longitudinal and transverse waves. Longitudinal: 𝑦 ( 𝑥 , 𝑡 ) = 𝐴 sin ⁡ ( 𝑘 𝑥 − 𝜔 𝑡 ) y(x,t)=Asin(kx−ωt). Transverse: Similar form, but for perpendicular displacements. What is phase and path difference? Phase: Angular difference. Path: Physical distance corresponding to the phase. Why rings are circular in Newton’s ring experiment? Symmetry of spherical wavefront and lens curvature. What is wavefront and wavelet? Wavefront: Surface of equal phase. Wavelet: Secondary wave source. Define relative dielectric constant. 𝜀 𝑟 = 𝜀 𝜀 0 ε r ​ = ε 0 ​ ε ​ .