Physics

When the lift is in free fall, the effective acceleration due to gravity inside the lift becomes zero. Since the time period of a simple pendulum is T = 2π√(l/g), if g becomes zero, the time period tends to infinity, meaning the pendulum does not oscillate.

Electrical resonance occurs when inductive and capacitive reactances in a circuit cancel each other, which is a principle used in both radios and microwave ovens for tuning and efficient energy transfer. Therefore, resonance is observed in both devices.

The least distance of distinct vision, or near point, typically increases with age due to the reduced flexibility of the eye's lens, a condition known as presbyopia. This makes option A correct.

When two convex lenses of equal focal length f are placed in contact, their combined focal length F is given by 1/F = 1/f + 1/f = 2/f, so F = f/2.

Photons are massless particles; their rest mass is exactly zero. This is a fundamental concept in physics, as photons always travel at the speed of light and cannot be at rest.

Microwaves heat substances containing water molecules by causing them to vibrate and generate heat. Milk, containing water, will heat up, but the cup (usually ceramic or glass) may also become warm due to heat conduction from the milk. Therefore, statement (1) that only milk will be heated is false, making option B the correct answer. Statements (2) and (3) are generally true depending on the cup material.

The restoring force on a simple pendulum is the component of the gravitational force acting along the arc of the pendulum's swing, which is mg sin θ, where θ is the angular displacement. This force acts to bring the pendulum back to its equilibrium position.

Using Einstein's mass-energy equivalence E=mc², 0.001 kg corresponds to energy E = 0.001 × (3×10^8)² = 9×10^{13} joules. Converting joules to GWh (1 GWh = 3.6×10^12 J), energy = 9×10^{13} / 3.6×10^{12} = 25 GWh. However, the calculation shows 25 GWh, so option B is correct. Rechecking calculation: 0.001 kg × (3×10^8 m/s)² = 9×10^{13} J; 9×10^{13} J / 3.6×10^{12} J/GWh = 25 GWh. Therefore, option B is correct, not C. The initial explanation was missing, so it is added here.

In photoemission, the kinetic energy of emitted photoelectrons is given by the equation K.E. = hf - φ, where h is Planck's constant, f is the frequency of incident radiation, and φ is the work function. Increasing the wavelength decreases the frequency (since f = c/λ), thus decreasing the kinetic energy of photoelectrons. Therefore, the average kinetic energy decreases with increasing wavelength.

At resonance, the energy absorbed by a body is maximum because the driving frequency matches the natural frequency, leading to maximum amplitude and energy transfer.