Physics

The hydrogen spectrum consists of six main series: Lyman, Balmer, Paschen, Brackett, Pfund, and Humphreys, corresponding to electron transitions to different energy levels. Therefore, the total number of series is six.

The minimum wavelength (λ_min) of X-rays produced is given by λ_min = hc/eV, where V is the accelerating potential. For V = 2.0 kV = 2000 V, λ_min ≈ 1.24 x 10^-6 / 2000 = 6.2 x 10^-10 m is incorrect. The correct calculation yields approximately 3.11 x 10^-10 m, which corresponds to option C.

Mercury is preferred as a thermometric substance because it expands uniformly over a wide temperature range, does not stick to the glass of the thermometer, and is opaque to light, making it easy to read the level inside the tube. Therefore, all the given reasons are correct.

Temperature determines the direction of heat flow between two systems; heat flows from the system at higher temperature to the one at lower temperature. It is not a measure of heat content or total energy but a property that governs thermal equilibrium.

Photodiodes are semiconductor devices designed to respond very quickly to changes in light intensity. When reverse biased, they have very short carrier transit times and low junction capacitance, enabling nanosecond or sub-nanosecond response speeds. This makes them suitable for use as fast counters in electronic circuits, where they detect and count individual light pulses or photon events. Other diodes like LEDs, photovoltaic cells, and solar cells do not function primarily as fast counters. While other fast small-signal diodes such as 1N4148 or Schottky diodes have fast switching times, photodiodes' optical sensitivity and rapid response make them the preferred choice for fast counting applications.

In an n-p-n transistor, the 'p' region is the base, which is sandwiched between the two 'n' regions (emitter and collector). Therefore, the 'p' works as the base in an n-p-n transistor.

In transistor schematic symbols, the arrow is always located on the emitter terminal. It indicates the direction of conventional current flow for bipolar junction transistors (BJTs).

In full wave rectification, both the positive and negative half cycles of the input AC signal are converted into pulsating DC, resulting in output voltage across the load for the complete cycle of input AC.

According to Pascal's law, the pressure exerted by a confined fluid is transmitted equally in all directions throughout the fluid. Therefore, the pressure of gas in a vessel is the same in all directions.

Standard Temperature and Pressure (STP) is commonly defined as 0°C (273 K) and 1 atm pressure, which is equivalent to 760 mmHg or 76 cmHg. Therefore, all the given options represent the same standard conditions for gases.