Practice MCQ Questions and answers on Physics-GK

Echolocation is an adaptation bats use to locate flowering plants, hunt insects in flight and find warm places for hibernation.

Bats are capable of avoiding obstacles that they encounter, even in complete darkness. This is because they emit ultrasound (high frequency sound) and analyse the echo produced when the sound hits objects on their path. Prey capture without the aid of echolocation by some bats is also described.

The formula of frequency is: f = c / ë = wave speed c (m/s) / wavelength ë (m), where f: frequency, c: wave speed, and ë: wavelength. As per the question, f = 300/0.3 = 1000 cycles/ seconds = 1000 Hz = 1 KHz.
Sound waves with frequencies above 20 KHz are called Ultrasonic; those below 20 Hz are called Infrasonic. Sound waves with frequencies between 20 Hz to 20,000 Hz are called audible waves.

Candela is the SI unit of luminous intensity.

Assuming air to be an ideal gas, the speed of sound depends on temperature only. As air temperature increases, so does the speed of sound and vice versa. The speed of sound is completely independent of air pressure because the air pressure and air density are proportional to each other at the same temperature.

Humidity has little effect on the speed of sound, nor does air pressure by itself. Air pressure has no effect at all in an ideal gas approximation. This is because pressure and density both contribute to sound velocity equally, and in an ideal gas the two effects cancel out, leaving only the effect of temperature.

Radar, electromagnetic sensor used for detecting, locating, tracking, and recognizing objects of various kinds at considerable distances. It operates by transmitting electromagnetic energy toward objects, commonly referred to as targets, and observing the echoes returned from them.

The velocity of sound in dry air is approximately 343 m/s at a temperature of 25 °C. Therefore, the reflecting object must be more than 17.2 m from the sound source for echo to be perceived by a person located at the source.

Sound travels fastest in glass.

Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency.