Physics

The electric potential energy (P.E.) of an electron in orbit around a positive charge is given by the formula U = -Ke^2/rn, where K is Coulomb's constant, e is the electron charge, and rn is the radius of the orbit. The negative sign indicates the attractive force between opposite charges.

In laser physics, having more atoms in the excited (upper) state than in the lower state is known as population inversion, which is essential for laser action to occur.

An insulator has the greatest energy gap (band gap) between its valence and conduction bands, which prevents free flow of electrons. Conductors have no significant band gap, and semiconductors have a smaller band gap than insulators.

According to Gay-Lussac's law, when the volume of a gas is held constant, increasing its temperature causes the pressure to increase proportionally.

The penetrating power of X-rays primarily depends on their frequency (or equivalently, their energy). Higher frequency X-rays have greater energy and thus greater penetrating ability. Applied voltage affects the frequency indirectly, but frequency is the direct factor determining penetration.

A transistor working as an amplifier operates similarly to a triode vacuum tube, as both control a large output current by a smaller input signal, enabling amplification.

A hydrogen-filled discharge tube emits light at specific wavelengths corresponding to electron transitions in hydrogen atoms, producing a line spectrum rather than a continuous or band spectrum.

A rectangular voltage waveform consists of discrete levels (high and low), which is characteristic of a digital waveform rather than an analogue or continuous waveform.

In a semiconductor diode under forward bias, the current is primarily due to the flow of majority carriers (electrons in n-type and holes in p-type regions) moving across the junction, which constitutes the forward current.

The minimum wavelength of X-rays emitted (the cutoff wavelength) is given by λ = hc / eV, where h is Planck's constant, c is the speed of light, e is the electron charge, and V is the accelerating voltage. This corresponds to option B.

A semiconductor diode acts as a rectifier because it allows current to flow easily in one direction (forward biased) due to low resistance, and blocks current in the opposite direction (reverse biased) due to high resistance, enabling conversion of AC to DC.

A non-inverting amplifier configuration typically has a very high input impedance because the input signal is applied to the non-inverting input of the op-amp, which draws negligible current. This characteristic is fundamental to its operation.

Semiconductors doped with donor atoms have extra free electrons, making them n-type semiconductors. P-type semiconductors have acceptor atoms creating holes, and 'mix' or 'any of above' are not standard classifications.

Internal energy is a state function representing the total energy contained within a system, including kinetic and potential energies at the molecular level. However, it is not simply the sum of all forms of energy associated with molecules, nor is it proportional only to translational kinetic energy. Therefore, option B is correct.

Light Emitting Diodes (LEDs) are semiconductor diodes specifically designed to emit light when current passes through them, making them ideal as indicator lamps in electronic circuits.

Transistors operate based on electrical current and voltage applied to their terminals, not by heating any part. Therefore, none of the options involving heating the emitter, base, or collector are correct.

Each electron carries a charge of approximately -1.6 × 10⁻¹⁹ coulombs. For one million (10⁶) electrons, the total charge is 10⁶ × (-1.6 × 10⁻¹⁹) = -1.6 × 10⁻¹³ coulombs. Therefore, the correct answer is option B: -1.6 × 10⁻¹³ coulombs.

Matter inherently possesses energy due to its mass, known as rest energy, which is described by Einstein's equation E=mc². This energy exists even when the matter is at rest, distinguishing it from other forms like potential or chemical energy.

Young's modulus measures the stiffness of a material and is defined only for solids, as it relates to elastic deformation under tensile or compressive stress. Gases and liquids do not have a defined Young's modulus because they cannot sustain shear stress in the same way solids do.

A rainbow is formed when sunlight is refracted, reflected, and dispersed by raindrops. To see a rainbow, the observer must have the Sun behind them and be facing the raindrops where the light is refracted. Therefore, the Sun remains behind us and we face the raindrops.

The Boltzmann constant (K) is related to the universal gas constant (R) and Avogadro's number (Na) by the formula K = R / Na. This expresses the gas constant per individual molecule rather than per mole.

Energy is defined as the capacity to do work. This is a fundamental concept in physics distinguishing energy from work, power, and momentum.

The SI unit with the symbol 'cd' is the candela, which measures luminous intensity. Other options like Cm (centimeter), Ampere (A), and Second (s) have different symbols and represent different quantities.

The velocity of sound in a gas at constant temperature depends primarily on the temperature and the properties of the gas, not on the pressure or atmospheric level. Since the temperature is assumed constant, the velocity of sound at 4 atmospheres is the same as at 1 atmosphere, making the ratio 1:1.

A petrol engine is a Spark Ignition (SI) engine because it ignites the air-fuel mixture using a spark plug. It is not a Compression Ignition (CI) engine, which is typical for diesel engines. While it is an Internal Combustion (IC) engine, the most specific and correct classification here is SI engine.