Physics MCQ

17 m

Explanation: An echo is heard distinctly if it reaches the ear at least 0.1 s after the original sound.
If d is the distance between the observer and the obstacle and V is the speed of sound, then the total distance travelled by the sound to reach the obstacle and then to come back is 2d and the time taken is,
t = Total distance travelled/Speed of sound = 2d/V
or, d = V t/2
Putting t = 0.1 s and V = 340 m/s in air at ordinary temperature, we get:
d = (340 x 0.1)/2 = 17 m
Thus, to hear an echo distinctly, the minimum distance between the source and the reflector in air is 17 m.

(a)
Explanation:
In ideal conditions, the body vibrates with the same amplitude and frequency forever.

(b)
Ultrasonic waves
Explanation:
Bats emit ultrasonic waves, which are sound waves with frequencies higher than 20 kHz, well above the human audible range, to navigate and locate objects through echolocation.

(c)
The reflecting surface must be larger than the wavelength of the sound wave
Explanation:
Sound waves reflect effectively off surfaces that are larger than their wavelength. When the reflecting surface is too small, the sound tends to diffract rather than reflect.

(b) Increases
Explanation:
The speed of sound in a gas increases with temperature because higher temperatures reduce the gas's density, allowing sound waves to travel faster.

(b)
Kinetic energy to potential energy and vice versa
Explanation:
When particles of the medium vibrate, they alternately convert kinetic energy (motion) into potential energy (position) and back, facilitating the propagation of the wave.

(c)
Longitudinal, transverse
Explanation:
Mechanical waves are classified into two main types: longitudinal waves, where particle displacement is parallel to wave motion, and transverse waves, where particle displacement is perpendicular to wave motion.

(c) forced vibrations
Explanation:
This is because the tuning fork forces the tabletop to vibrate at its own frequency.

(b)
X will be grave and Y will be shriller
Explanation:
Greater the frequency more would be the shrillness.

(a)
Waveform
Explanation:
Musical characteristic identified due to different sources is called waveform

(c)
forced vibrations
Explanation:
When a body vibrates under a periodic force the vibrations of the body are forced vibrations, as they are driven by an external force.

(b)
Sound with high frequency
Explanation:
Pitch is the feature of sound that distinguishes an acute (or shrill) noise from a grave or flat tone. Sound with high frequency also known as Shrill.

(a)
Unique waveform of vocal cord of an individual
Explanation:
Every individual have their unique waveform of vocal cord. By that we can identify any person without seeing him/her.

(a)
l-(i), II-(ii), III-(iii), IV-(iv)
Explanation:
Lowest level of loudness is 0 dB, which a man can hear. Approximately, sound in the range of 0-80 dB is categorised as safe limit of level of sound, Sound of level 10 dB to 30 dB has a soothing sensation. Sound of greater than 120 dB can
potentially damage the ears of listerner.

(b)
Converts sound waves to electrical signals, which are subsequently amplified before being converted back to sound waves.
Explanation:
Hearing aid is an electronic device used by people with hearing loss. It first converts sound waves to electrical signals, which are subsequently amplified by an amplifier before being converted back to clear and louder sound waves.

(a) I-II-III
Explanation:
To minimize the disturbances and clear recording, the noise level or sound level in a music recording studio should be kept to a minimum. Jet aircraft make substantially more noise and a lot larger sound wave than heavy traffic. As a result, the correct order is (a).

(a)
Less than 20 Hz
Explanation:
Human hearing typically ranges from 20 Hz to 20,000 Hz. Frequencies below 20 Hz are considered infrasonic and are not audible to the human ear. Therefore, if a pendulum vibrates at a frequency low than 20 Hz, its sound would not be audible.

(b)
Forced vibration
Explanation:
In forced vibration, the vibrations of the body takes place under the influence of an external periodic force acting on it.

(b)
Damped vibration
Explanation:
Damped vibration, as due to resistance of the medium the amplitude will decrease with time and stop at the end.

(b)
Explanation:
In damped vibrations, the amplitude of the vibrating body continuously decreases with time and finally it stop vibrating.

(b)
Free
Explanation:
In free vibrations the amplitude remains constant with time due to absence of any external resistive force. Thus, it is free vibration.

(b)
No external force is applied.
Explanation:
Free vibrations are the vibrations of a body that occur in the absence of any external force and the vibration is determined by the body's form and size.

(c)
(i)-4, (ii)-3, (iii)-2, (iv)-1
Explanation:
In a vacuum, light waves can travel. Sound wave cannot travel in space because it require a medium to propagate. Infrared rays are used in TV remote controls. Satellite communication is transmitted via radio waves.

(d)
both (b) and (c)
Explanation:
Bats can produce and detect high frequency sound waves of about 100 kHz that does not lie in human audible range. These waves are used to locate obstacle at right. These sound waves strike any obstacle in their path and are reflected as echoes to the bat's ear.

(c)
echo cardiogram
Explanation:
An echocardiogram checks how your how your heart's chamber and values are pumping blood through your heart.

(c)
sound absorbers such as foam board

(d)
reverberation
Explanation :
Reverberation is the phenomenon where sound wave inside on enclosed space persist due to repeated reflections from different surfaces.

(b)
reflection of sound
Explanation:
Submarines can use sonar systems, which operate on the principle of sound reflection to assess the spread and movement of glaciers in the Arctic region.

(a)
echo
Explanation:
Super sonic war planes use radar, employing the echo principle with radio-waves to detect and track targets by reflecting waves off them.

(d)
both (a) and (c)
Explanation :
Bats use echolocation, which involves the reflection of sound and the concept of echo to locate and catch their prey.

(d)
detect the depth of sea bed
Explanation:
SONAR (Sound Navigation And Ranging) uses sound waves to map or navigate underwater environments, including measuring the depth of the sea bed, which is one of its primary applications.

(c)
greater than 17 m
Explanation:
An echo is perceptible when the one-way distance between the source and listener is over 17 metre allowing sufficient time for sound to travel, reflect and be distinguished as a separate sound.

(b)
homogeneous medium
Explanation:
A homogeneous medium has uniform properties throughout its volume. Since change of frequency and wavelength does not affect the speed of sound in same medium. Therefore velocity of sound is constant in homogeneous medium.

(a)
compression and rarefactions
Explanation:
Sound waves are longitudinal waves, which means they propagate through the compression and rarefaction of the medium they travel through.

(d)
all of the above