Physics

The production of heat when an electric current passes through a conductor is known as the Joule effect, named after James Prescott Joule. This phenomenon explains how electrical energy is converted into heat energy in resistive materials.

Sound waves are mechanical waves that require a material medium (solid, liquid, or gas) to propagate. Since a vacuum lacks any material particles, sound cannot travel through it.

In liquids and gases, electric current is carried by the movement of both negative charges (electrons or anions) and positive charges (cations). This is because these media contain ions of both polarities that move under an electric field, producing current.

According to Newton's theory, sound travels in air under adiabatic conditions because the compression and rarefaction of air during sound propagation occur too rapidly for heat exchange, making the process adiabatic rather than isothermal.

The trajectory of a projectile under the influence of gravity, neglecting air resistance, is a parabola. This is because the horizontal motion is uniform while the vertical motion is uniformly accelerated, resulting in a parabolic path.

The fundamental frequency of an open pipe is twice that of a closed pipe of the same length because an open pipe supports a full wavelength, while a closed pipe supports only a quarter wavelength, resulting in fopen = 2 × fclosed.

Given three equal resistors each dissipate 10 W when connected in series, the total power dissipated in series is 30 W. The equivalent resistance in series is 3R. Using the same emf, when connected in parallel, the equivalent resistance becomes R/3. Power dissipated is inversely proportional to resistance for the same voltage, so power in parallel is 9 times the power in series (since resistance is 1/9th). Therefore, total power in parallel is 30 W × 9 = 270 W. However, since the question asks for the power dissipated by the combination and the options do not include 270 W, the closest correct interpretation is that each resistor dissipates 90 W in parallel, making total power 270 W. The original answer 'C' (100 W) is incorrect; the correct answer is 'B' (90 W) if interpreted as power per resistor, or 270 W total power. The question and options should clarify whether total or per resistor power is asked. Based on common interpretation, the correct answer is B (90 W) per resistor in parallel.

Newton estimated the speed of sound in air to be approximately 281 m/s based on his theoretical calculations, which was lower than the actual measured speed due to neglecting the effect of air's heat capacity. This makes option A correct.

The power rating is 500W (0.5 kW). Units consumed = Power (kW) × Time (hours) = 0.5 × 24 = 12 units. However, the voltage rating is 20V, which is unusually low for an iron, but since power and time are given, we use power to calculate units. The correct units consumed is 12, which corresponds to option A, not B. Therefore, the correct answer is A.

Current (I) is charge (Q) per unit time (t), so Q = I × t. Given I = 1 A and t = 1 hour = 3600 seconds, Q = 1 × 3600 = 3600 C. However, the question asks for charge flow through a 2 m conductor, but length does not affect charge flow for a given current. Therefore, the charge flow in 1 hour is 3600 C, which corresponds to option A. The original correct_answer was A, which is correct.