Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
Solution and Explanation
Thunder and lightning occur simultaneously. It is known that the speed of light in air is [\(3\times10^8m/s\)], while the speed of sound in air is [\(330\ m/s\)].
Because the speed of light is significantly greater than the speed of sound, the flash is observed well before the sound of thunder during a lightning event.
Top Questions on Propagation of Sound
- A sound wave travels at a speed of 339 ms–1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
- CBSE Class IX
- Science
- Propagation of Sound
- What is loudness of sound? What factors does it depend on?
- CBSE Class IX
- Science
- Propagation of Sound
- A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top?
Given, g = 10 ms–2 and speed of sound = 340 ms–1.- CBSE Class IX
- Science
- Propagation of Sound
- The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?
- CBSE Class IX
- Science
- Propagation of Sound
- Why is sound wave called a longitudinal wave?
- CBSE Class IX
- Science
- Propagation of Sound
Questions Asked in CBSE Class IX exam
- Match the phrases in Column A with their meanings in Column B.
A B (i) broke out (a) an attitude of kindness, a readiness to give freely (ii) in accordance with (b) was not able to tolerate (iii) a helping hand (c) began suddenly in a violent way (iv) could not stomach (d) assistance (v) generosity of spirit (e) persons with power to make decisions (vi) figures of authority (f) according to a particular rule, principle, or system - CBSE Class IX
- My childhood
ABC is a triangle in which altitudes BE and CF to sides AC and AB are equal (see Fig). Show that
(i) ∆ ABE ≅ ∆ ACF
(ii) AB = AC, i.e., ABC is an isosceles triangle.
- CBSE Class IX
- Some Properties of a Triangle
- The author speaks both of people who were very aware of the differences among them and those who tried to bridge these differences. Can you identify such people in the text?
- CBSE Class IX
- My childhood
- What did his father say to this?
- CBSE Class IX
- My childhood
- The following data on the number of girls (to the nearest ten) per thousand boys in different sections of Indian Society is given below:
Section
Number of girls per thousand boys Scheduled Caste (SC)
940
Scheduled Tribe (ST)
970
Non-SC/ST
920
Backward districts
950
Non-backward districts
920
Rural
930
Urban
910
(i) Represent the information above by a bar graph.
(ii) In the classroom discuss what conclusions can be arrived at from the graph.- CBSE Class IX
- Graphical Representation of Data
Concepts Used:
Sound
Sound is a vibration that propagates the mechanical wave of displacement and pressure, through a medium can be of any matter. In other words, the sound is the thin line between Music sound and Noise.
Types of Sounds:
Sound can be divided into two types depending on its frequency. The following are:-
Infrasonic Waves:
- Infrasonic waves have a frequency lower than 20 Hz. Since it is below the human hearing range, it is inaudible to humans.
- However, several other living organisms use these waves to communicate, whales, sharks, elephants, hippopotamus, etc. these waves are also used in the scientific field, it is used to study upcoming earthquakes, volcanic eruptions, human heart rates, rock formation stages, etc.
Ultrasonic waves:
- Ultrasonic waves have a frequency higher than 20 kHz. Since it is above the human hearing range, it is inaudible to humans.
- These waves are used in the scientific field, it is used to study human heart rates, to take sonograms, navigation of directions, imaging things, uniform sample mixing, communication, testing of samples, etc.