Physics

Mechanical waves require a material medium (solid, liquid, or gas) to propagate, unlike electromagnetic waves which can travel through a vacuum. Therefore, the correct answer is mechanical waves.

The Doppler effect is used to estimate the velocity of a star relative to Earth by observing the shift in the star's spectral lines. Interference and beats phenomena are related to wave behavior but are not used for measuring stellar velocities.

The resistance of a conductor depends on the nature of the conductor (material), its dimensions (length and cross-sectional area), and its physical state (such as temperature). Therefore, all the given factors affect resistance.

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points, resulting in a straight line when voltage is plotted against current on a graph.

Projectile motion refers to the motion of an object thrown or projected into the air, subject only to gravity and air resistance. A gas-filled balloon does not follow a parabolic trajectory like projectiles; instead, it floats due to buoyant forces, so it is not an example of projectile motion.

A 40 W bulb uses 40 joules of energy per second. Over one hour (3600 seconds), the total energy converted to heat is 40 W × 3600 s = 144,000 J. This energy is primarily released as heat.

The velocity of sound in dry air increases by approximately 0.6 m/s for each 1°C rise in temperature. This is a well-established physical fact and is commonly approximated as about 0.6 m/s per degree Celsius. Among the given options, 0.61 m/s (option C) is the closest and most accurate value. The originally marked answer (A: 1.61 m/s) is incorrect as it overestimates the increase by more than double.

Copper is the best material for making connecting wires because it has excellent electrical conductivity, is relatively inexpensive, and is ductile, making it easy to draw into wires. While silver has slightly better conductivity, it is much more expensive and less commonly used for wiring.

The fundamental frequency of a stationary wave in an open pipe is twice the fundamental frequency of a stationary wave in a closed pipe of the same length because an open pipe supports a full wavelength while a closed pipe supports only a quarter wavelength for the fundamental mode.

Tungsten is used for bulb filaments because it has a very high melting point and good electrical resistance, making it ideal for glowing brightly without melting. The other materials either have lower melting points or are not suitable for filament use.

An open organ pipe supports standing waves with displacement antinodes at both ends, allowing both even and odd harmonics to be present in the sound produced.

The energy stored per unit volume (strain energy density) in an elastic material is given by (1/2) × Young's modulus × (strain)^2, which corresponds to (Y∝²)/2. This matches option C.

Work done by a force is given by W = Fd cosθ, where θ is the angle between force and displacement. The work is maximum when cosθ = 1, which occurs at θ = 0°, meaning force and displacement are in the same direction.

The dot product of force and velocity gives power, which is the rate at which work is done. This is because power = force · velocity (dot product).

Geothermal energy is derived from the natural heat of the Earth, which is continuously produced and thus considered a renewable source of energy. It is sustainable and does not deplete over time like fossil fuels.

The slope of a work versus time graph represents the rate of change of work with respect to time, which is power. Power is defined as the work done per unit time (P = ΔW/Δt) and is measured in watts (joules per second). Therefore, the slope of a work vs time graph corresponds to power, not displacement, acceleration, or energy. Option C (power) is the correct answer.

The central spot of Newton's rings is dark because there is a path difference of half a wavelength due to the air film between the lens and the glass plate, causing destructive interference at the center.

Gravitational potential energy (P.E.) of a body is given by the formula mgh, where m is mass, g is acceleration due to gravity, and h is height. Therefore, it has a specific formula.

The appearance of color in thin films is due to interference of light waves reflected from the different surfaces of the film, causing constructive and destructive interference at different wavelengths.

Diffraction fringes produced by a single slit or double slit are generally equally spaced due to the consistent path difference between adjacent maxima or minima. Therefore, the distance between fringes remains constant, making option A correct.

Materials that undergo plastic deformation before breaking are called ductile materials because they can deform significantly without fracturing. Brittle materials break without noticeable deformation, amorphous refers to non-crystalline structure, and polymers are a class of materials that can be ductile or brittle.

The property where the angular position of cells remains the same in a crystal sample refers to the external symmetry of form, which describes the consistent geometric arrangement and symmetry of crystal faces.

Light from the Sun takes approximately 8 minutes to reach the Earth, as the average distance is about 150 million kilometers and light travels at about 300,000 kilometers per second.

Kinetic energy (K.E.) is given by K.E. = p²/(2m), where p is momentum and m is mass. Since all particles have the same momentum, the particle with the smallest mass will have the highest kinetic energy. Among proton, electron, neutron, and alpha particle, the electron has the smallest mass, so it has the highest kinetic energy.

In a simple cubic crystal structure, one atom is located at each of the eight corners of the cube. Each corner atom is shared among eight adjacent cubes, resulting in one atom per unit cell.