Physics

When a sound source moves away from a stationary listener, the sound waves are stretched, leading to a decrease in the frequency perceived by the listener. This phenomenon is known as the Doppler effect, resulting in an apparent decrease in frequency.

Ultrasonic waves are sound waves with frequencies higher than the audible range for humans, which is above 20 kHz. Therefore, option B correctly describes ultrasonic waves.

Power consumption is calculated as Power (in kW) × Time (in hours). Here, 400 watts = 0.4 kW, and time = 5 hours. So, energy consumed = 0.4 kW × 5 h = 2 kWh.

A wire with a very high value of conductance allows electric current to flow easily, which means it is a very good conductor. Conductance is the reciprocal of resistance, so higher conductance indicates better conductivity.

The rate at which electrical energy is converted to heat in a resistor is the power dissipated, given by Joule's law as P = I²R, where I is the current and R is the resistance. This formula represents the power (energy per unit time), not the total energy. The formula I²Rt (option C) represents the total heat energy generated over time t, not the rate. Therefore, the correct answer for the rate of conversion (power) is option B: I²R.

The velocity of sound in air at temperature T (in °C) can be approximated by the formula c = 331.3 + 0.606 T (m/s). At 0°C, the velocity is about 331.3 m/s. To double this velocity, we want c = 2 × 331.3 = 662.6 m/s. Using the formula, 662.6 = 331.3 + 0.606 T, solving for T gives T = (662.6 - 331.3) / 0.606 ≈ 547°C. Among the options given, 586°C (option B) is the closest and most reasonable choice. The original question's explanation using the square root of temperature in Kelvin is an approximation valid for ideal gases, but the linear approximation with temperature in Celsius is more commonly used for air and matches the data better. Therefore, the correct answer is B (586°C).

In a typical interference pattern, such as from a double-slit experiment, the bright and dark fringes alternate with equal spacing, meaning both have approximately equal widths. This is because the path difference changes uniformly, producing fringes of equal size.

The distance between any two consecutive crests or troughs in a wave is called the wavelength. This is a fundamental property of waves, distinguishing it from frequency, period, or phase difference.

The speed of sound in hydrogen is approximately three times faster than in oxygen because hydrogen molecules are much lighter, allowing sound waves to travel faster through it.

When a body moves in a straight line, its displacement is equal to the distance traveled because displacement is the shortest path between the initial and final points, which in a straight line is the same as the distance. Options B and C are unrelated to displacement, and D is incorrect because force is not related to displacement.