CBSE Class 7 Science Advanced Physics Sound Very Short Answer Questions Set 03

Very Short Answer Questions

Question 1. State whether the following statement is true or false.
Sitar, veena and guitar are some percussion instruments.
Answer:
False. They are stringed instruments.
In simple words: These have vibrating strings, not struck membranes.

Teacher's Note:
1. Percussion instruments have stretched membranes, such as the tabla.
2. Check the part that vibrates.

Question 2. State whether the following statement is true or false.
The sounds of frequencies greater than 20 kHz are called ultrasonic sounds.
Answer:
True
In simple words: Above 20 000 Hz the sound is ultrasonic.

Teacher's Note:
1. Humans cannot hear them.
2. Bats and dogs can.

Question 3. State whether the following statement is true or false.
Sound travels much faster than light in a given medium.
Answer:
False. Light is much faster than sound.
In simple words: Light is far faster, so we see lightning before we hear thunder.

Teacher's Note:
1. Light: 3 × 10⁸ m s⁻¹, sound in air: about 330 m s⁻¹.
2. This is the basis of finding the distance of a cloud.

Question 4. State whether the following statement is true or false.
The velocity of sound is more in vacuum than in any other medium.
Answer:
False. Sound cannot travel in a vacuum, so its velocity there is zero.
In simple words: Without a medium there is no sound at all.

Teacher's Note:
1. The bell jar experiment demonstrates this.
2. Sound needs particles to pass on the vibrations.

Question 5. State whether the following statement is true or false.
In general, the voice of a woman has a higher frequency than that of a man.
Answer:
True
In simple words: A woman's voice is shriller, so its frequency is higher.

Teacher's Note:
1. Shorter, thinner vocal cords give a higher frequency.
2. Children have even higher voices.

Question 6. Fill in the blank.
1 kHz = ________ Hz.
Answer:
1000
In simple words: Kilo means a thousand.

Teacher's Note:
1. 1 MHz = 10⁶ Hz.
2. Use kilo for thousand, mega for million.

Question 7. Fill in the blank.
The vibratory motion of a tuning fork is ________ in nature.
Answer:
periodic. It repeats itself after equal intervals of time.
In simple words: The same motion is repeated at regular intervals.

Teacher's Note:
1. It is also oscillatory.
2. Periodic means regular repetition.

Question 8. Fill in the blank.
The time period of a simple pendulum is independent of ________ of oscillation.
Answer:
amplitude
In simple words: How far the bob swings does not change the time of one swing.

Teacher's Note:
1. The time period depends on the length of the pendulum.
2. This is true for small swings.

Question 9. Fill in the blank.
The loudness of sound is determined by its ________.
Answer:
amplitude
In simple words: Larger vibrations give a louder sound.

Teacher's Note:
1. Frequency decides the pitch, not the loudness.
2. The unit of loudness is the decibel.

Question 10. Fill in the blank.
________ sound is used as a diagnostic tool in medical science.
Answer:
Ultrasound (ultrasonic sound)
In simple words: Ultrasound scans show the inside of the body.

Teacher's Note:
1. Sonography uses reflected ultrasound.
2. It is safe for checking a baby in the womb.

Question 11. Fill in the blank.
Sound needs a ________ to travel.
Answer:
medium
In simple words: Sound is passed on by the particles of a material.

Teacher's Note:
1. Solids, liquids and gases are media.
2. A vacuum is not.

Question 12. Fill in the blank.
Humans are sensitive to sound of loudness from ________ to ________.
Answer:
10 dB to 180 dB (as given in the book)
In simple words: The book gives this as the range the human ear can sense.

Teacher's Note:
1. More than about 90 dB is painful.
2. 50 to 60 dB is normal.

Question 13. Fill in the blank.
The loudness of sound ________ with increase in the energy spent to vibrate a body.
Answer:
increases
In simple words: More energy makes bigger vibrations and louder sound.

Teacher's Note:
1. Energy raises the amplitude.
2. It does not change the pitch.

Question 14. Fill in the blank.
Propagation of sound can be visualized as propagation of ________ in the medium.
Answer:
pressure variations (compressions and rarefactions, or density variations)
In simple words: A sound wave is a moving pattern of high and low pressure.

Teacher's Note:
1. Compressions are high pressure, rarefactions are low pressure.
2. The particles only vibrate about their positions.

Question 15. Fill in the blank.
A frequency of 1 Hz means ________ oscillation(s) per second.
Answer:
one
In simple words: 1 Hz is one oscillation each second.

Teacher's Note:
1. Hertz is oscillations per second.
2. Time period is then 1 s.

Teacher's Note:
1. Dolphins find prey with echoes.
2. Carpets absorb sound instead of reflecting it.

Teacher's Note:
1. Strings, membranes, air column and solid struck bodies are the four groups.
2. Sonar uses echoes.

Teacher's Note:
1. The syrinx is a bird's sound organ.
2. Scanning of internal organs uses ultrasound.