9th
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- The speed of sound in air at 0°C is 332m/s. If it increases at the rate of 0.6m/s per degree, Let T be the temperature at which velocity of sound is 344m/s. Then the velocity of sound increased from 0°C to T°C would be = 344 - 332= 12... 1
- Where and why sound absorbing materials are used? The sound absorbing materials are used in constructing the roofs and walls of conference halls, auditorium halls and theatre so that the sou... 1
- What should be the dimensions and the shape of classrooms so that no echo can be produced there? The dimensions of classroom should be made such that we can’t hear an echo is the classroom should be square shaped and the distance between... 1
- Study the construction of the Golghumat at Vijapur and discuss the reasons for the multiple echoes produced there. Goighumat with a height of 51 metres and diameter of 37 metres with 3 metres thick walls is spread over approximately 1700 square metres. Th... 1
- What is an echo? What factors are important to get distinct echo? An echo is the repetition of the original sound because of reflection by some surface. At 22°C, the velocity of sound in air is 344 m/s. Our... 1
- We cannot hear an echo produced in a classroom. Our classrooms are mostly constructed in a such way that the distance between two walls of the classroom would be less than 17m. When there... 1
- The intensity of reverberation is higher in a closed and empty house. In a closed and empty room there will be no objects like furniture and other things. Due to which the sound generated reflects from the wall... 1
- The roof of a movie theatre and a conference hall is curved. The roof of movie theatre and a conference are made curved because when sound is reflected from curved roof and also from walls, it reach to... 1
- Fill in the blanks and explain. a) Sound does not travel through vacuum. Since, sound waves are longitudinal waves which requires medium for their propagation and hence doe... 2
- When a person stands in front of a plane mirror, how is the image formed? What is the nature of the image? The image of a person is formed from every point of the source, thereby forming an extended image of the whole source. The image formed woul... 1
- Which letters of the English alphabet form images that look the same as the original letters? A, H, I, M, O, T, U, V, W, X, Y 2
- If we hold a page of a book in front of a mirror, we see laterally inverted letters in the mirror. Why does it happen? When we hold a page of a book in front of the mirror, the image of the words appear laterally inverted. The image of every point of the word... 1
- difference between Principal Focus of Concave and Convex Mirror. Principal Focus of the Concave Mirror Principal Focus of the Convex Mirror (i) Incident rays which are parallel to the principal axis of a c... 1
- What is a mirror ? A mirror is a reflecting surface which reflects light and creates clear images. 2
- What is light ? Light is a form of electromagnetic radiation that produces the sensation of vision. 2
- Three mirrors are created from a single sphere. Which of the following- pole, center of curvature Three mirror created from single sphere Centre of curvature and Radius of curvature will be common for all three pieces. Pole and Principal... 1
- A 10cm long stick is kept in front of a concave mirror having focal length of 10cm in a such Given that, For concave mirror For end A: Focal length f= -10cm Object distance u = -30cm We know that, the mirrors formula is given by, 1/f... 1
- A convex mirror has a focal length of 18cm. The image of an object kept in front of the mirror is half the height of Given that, For convex mirror, Focal length f= 18cm And h2= h1/2 Hence, h2/h1 = 1/2 We know that, magnification is given by, m= h2/h1 = -v/u... 1
- An object of height 7cm is kept at a distance of 25cm in front of a concave mirror. The focal length of the mirror is Given that, For concave mirror, Object height h1= 7cm Object distance u= -25cm Focal length f= -15cm We know that, the mirrors formula is gi... 1
- Which type of mirrors are used in the following. Periscope, floodlights, shaving mirror, kaleidoscope, street lights In periscope plane mirror is used. In floodlights and shaving mirror the concave mirror is used. In kaleidoscope also plane mirror is used.... 1
- Draw the ray diagram for the cases of images obtained in concave mirror as described in the table on page 122. (a) A ray diagram for object at infinity for a concave mirror. Object at infinity for a concave mirror Image position Nature of image At foc... 1
- What sign conventions are used for reflection from a spherical mirror? According to the Cartesian sign convention, the pole of the mirror is taken as the origin. The principal axis is taken as the X-axis of the... 1
- If a spherical mirror breaks, what type of the mirrors are the individual pieces? After breaking of the spherical mirror there will be no change in the nature of the mirror. That means if the concave mirror is broken into... 1
- Why does obtaining the image of the sun on a paper with the help of a concave mirror burn the paper? We know that, when a parallel beam of light which may parallel to principal axis is incident on the concave mirror then after reflection the... 1