Physics

When light is incident normally on a thin film, the path difference between the reflected rays depends on the thickness of the film, the refractive index (nature) of the film, and the angle of incidence. However, at normal incidence, the angle of incidence is zero, so it does not affect the path difference. The path difference is given by 2 * thickness * refractive index of the film. Therefore, the path difference depends on both the thickness and the nature (refractive index) of the film. Since the angle of incidence is zero, it does not contribute, but the question's options do not separate thickness and nature clearly. The best correct choice is that the path difference depends on all three factors (thickness, nature, and angle), but practically at normal incidence, angle is zero and does not affect it. Hence, option D is the most accurate answer given the options.

In semiconductors, both electrons and holes act as charge carriers, contributing to electrical conduction. Electrons are negatively charged, while holes represent the absence of an electron and behave like positive charge carriers.

A completely filled band in a solid is called the valence band, which contains electrons bound to atoms and is fully occupied at absolute zero temperature. The conduction band is typically partially filled or empty, allowing electron movement.

Friction always opposes the direction of motion, so the work done by friction is negative as it removes energy from the system.

The area under a force-displacement graph represents the work done by the force over that displacement, as work is defined as the integral of force with respect to displacement.

The propulsion force of a rocket is a non-conservative force because it involves the expulsion of mass and energy, resulting in energy dissipation and not conserving mechanical energy within the system.

The Curie temperature is the temperature at which a ferromagnetic material loses its permanent magnetic properties and becomes paramagnetic due to thermal agitation overcoming magnetic ordering.

The metre was historically defined in terms of the wavelength of the red cadmium spectral line, a definition established by Albert A. Michelson. This definition linked the unit of length to a specific physical constant, improving precision in measurements.

The magnetic force per unit positive charge moving perpendicular to the magnetic field with unit velocity defines the magnetic field intensity (also called magnetic field strength). Magnetic induction refers to the magnetic flux density, which is related but not the force per unit charge and velocity.

Many semiconductors, such as silicon and germanium, crystallize in the face-centred cubic (FCC) structure, specifically the diamond cubic lattice, which is a variation of FCC. This structure is crucial for their semiconductor properties.

Power is defined as the rate of doing work or energy transfer per unit time. Since work has the dimension [ML^2T^{-2}] and time has the dimension [T], power has the dimension [ML^2T^{-3}].

A wave front is defined as the locus of all points in a medium that have the same phase of vibration, meaning they oscillate together. This matches the definition given in the question, making option D correct.

The work done against gravity when raising a body is calculated using the formula W = m × g × h, where m is the mass, g is the acceleration due to gravity (approximately 9.81 m/s²), and h is the height raised. For a mass of 2 kg raised through 2 meters, the work done is W = 2 × 9.81 × 2 = 39.24 J, which rounds to 39.2 J. Therefore, the correct answer is option C (39.2 J). The originally given option A (38.2 J) is incorrect as it does not match the calculation.

Escape velocity is the minimum speed needed for an object to escape from the gravitational field of a body without further propulsion. It depends on the mass and radius of the Earth (or the central body) and the gravitational constant, but it is independent of the mass of the escaping object. The angle at which the object is thrown affects the trajectory but not the minimum speed required to escape. Therefore, the escape velocity is independent of the object's mass, making option A correct.

When a light ray travels from a rarer to a denser medium and reflects, it undergoes a phase change of 180° (or π radians). This is a fundamental concept in wave optics related to phase shifts upon reflection.

Two light sources are considered coherent if they emit waves of the same wavelength and maintain a constant phase difference, which is essential for producing stable interference patterns.

Work done is force times distance. Both lift weights through the same distance, but the man lifts a heavier weight, so he does more work. However, power is work done per unit time. The child lifts a lighter weight but does it much faster, resulting in greater power output. Thus, the child does more work per second (more power).

Friction is a non-conservative force because it dissipates mechanical energy as heat, unlike electric, gravitational, and magnetic forces which are conservative and conserve mechanical energy in a closed system.

Escape velocity from a celestial body can be calculated using the formula v = sqrt(2gr), where g is the acceleration due to gravity on the surface and r is the radius of the body. Given g = 1.6 m/s² and r = 1600 km = 1,600,000 m, the escape velocity is v = sqrt(2 × 1.6 × 1,600,000) = sqrt(5,120,000) ≈ 2263 m/s or about 2.26 km/s. This matches option D (2263 m/s). The originally stated correct answer (C) is incorrect. The explanation in the question also correctly calculates the escape velocity but mistakenly identifies option D as correct while the answer key says C. The correct answer is D.

Cleavage is the property of crystals to break along specific planes of weakness, resulting in smooth, flat surfaces. This is a characteristic feature distinguishing cleavage from other properties like symmetry or isotropy.

Diffraction is more pronounced at sharp edges than at rounded edges. A sharp edge causes an abrupt truncation of the wavefront, generating strong diffraction effects such as pronounced bending and interference patterns. Rounded edges provide a smoother transition for waves, reducing the abruptness of the wavefront disturbance and thus decreasing the diffraction effect. This is supported by practical examples such as speaker cabinet design, where rounding edges reduces diffraction-related sound distortions, typically by about 1 dB in the mid-high frequency range.

Materials where valence electrons are tightly bound to their atoms at low temperatures do not allow free movement of electrons, making them insulators. This restricts electrical conductivity, distinguishing them from conductors and semiconductors.

Average power equals instantaneous power when work is done at a uniform rate because power is the rate of doing work. If the rate is constant, the instantaneous power at any moment matches the average power over the time interval.

A magnetometer is an instrument specifically designed to detect and measure very weak magnetic fields, making it the correct choice. Squids are animals, MRI is a medical imaging technique that uses magnetic fields but does not detect weak fields externally, and an oscilloscope measures electrical signals, not magnetic fields.

Energy consumed is power multiplied by time. For a 60 watt bulb running for 2 seconds, energy = 60 W × 2 s = 120 joules. However, the options given are 120 J (A), 60 J (B), 30 J (C), and 0.02 J (D). The correct calculation yields 120 J, which corresponds to option A, not C. Therefore, the correct answer is A.