Model Test – Solved ഉത്തരങ്ങൾ
Every question of the model paper, in the same order, with the full answer, the marking scheme, an animated figure or working for the numericals and explanation questions, and a link to the page where the idea is taught. Try each one again before you open the answer, and mark your own paper honestly.
Air particles are small blue dots; where they crowd together is a compression (C, മർദം കൂടിയ മേഖല), where they spread out a rarefaction (R, മർദം കുറഞ്ഞ മേഖല). Each particle only moves to and fro about its own place – the disturbance travels. Blue arcs are sound spreading out, yellow lines are light. Every number in the animations is worked out with distance = speed × time, the speeds of Table 8.3, 350 m/s for air in the textbook’s examples, and 3 × 108 m/s for light.
💡 Touch a ringing bell or a struck tuning fork – what do you feel?
Every source of sound (ശബ്ദസ്രോതസ്സ്) – a bell, a tuning fork, a veena string, our vocal cords – makes sound only while it vibrates, moving rapidly to and fro. Hold the prongs of a ringing tuning fork tightly: the vibration stops and so does the sound.
Marking: 1 mark.
📖 Review this on Page 5 · Key box 2
💡 Which one has no particles at all?
Sound needs a medium (മാധ്യമം) – a solid, a liquid or a gas – to travel. A vacuum has no particles to pass the vibrations on, so sound cannot travel through it. (Steel, water and air all carry sound.)
Marking: 1 mark for (d).
📖 Review this on Page 6 · Key box 4
💡 Solid, liquid or gas – which is fastest?
Table 8.3 (25 °C): aluminium 6423 m/s, sea water 1525 m/s, helium 968 m/s, air 347 m/s. Sound travels fastest in solids and slowest in gases.
Marking: 1 mark for (d).
📖 Review this on Page 7 · Table 8.3
💡 What is inside a flute that can vibrate?
In the tabla the stretched skin vibrates; in the odakkuzhal (ഓടക്കുഴൽ) nothing solid vibrates – the air column inside the flute is the main vibrating part.
Marking: 1 mark (“air” also accepted).
📖 Review this on Page 5 · Main vibrating parts
💡 Touch your throat while you speak.
Our voice is produced when the vocal cords in the larynx (സ്വനപേടകം) at the top of the windpipe vibrate. Touch your throat while speaking loudly – you can feel it.
Marking: 1 mark.
📖 Review this on Page 5 · Our voice
💡 Which part works like the balloon diaphragm in the bottle activity?
The pressure variations of sound travel down the ear canal (കർണ്ണനാളം) and make the eardrum (tympanum) vibrate, like the balloon diaphragm with the mustard seeds. It passes the vibrations on to the inner ear.
Marking: 1 mark for (c).
📖 Review this on Page 8 · The eardrum, key box 7
💡 In three of them you strike a stretched skin.
Veena. Its main vibrating part is its strings. In the chenda, the mridangam and the tabla, a stretched skin (membrane) vibrates.
Marking: ½ mark for “veena”, ½ mark for the reason.
📖 Review this on Page 5 · Table 8.1 · Page 11 · Let us assess Q5
💡 He is from Kollam district.
Resul Pookutty (born 1971, Vilakkupara, Anchal) won the Oscar for sound mixing (ശബ്ദമിശ്രണം), and also a BAFTA and the Padma Shri.
Marking: 1 mark.
📖 Review this on Page 9 · Resul Pookutty box
💡 distance = speed × time; the light arrives almost instantly.
Given: speed of sound v = 350 m/s; time t = 4 s
Formula: distance = speed × time
Substitution: 350 m/s × 4 s
Answer: distance = 1400 m = 1.4 km
The light of the flash (3 × 108 m/s) reaches Arun almost at once, so the 4 s is the time the sound took.
Marking: Formula ½, substitution ½, answer with unit 1.
📖 Review this on Page 7 · Firecracker, 1050 m · Page 4 · Speed, distance and time
💡 What is there between two astronauts on the Moon?
(a) The Moon has no atmosphere – no air. Sound needs a medium to travel, so the vibrations of one astronaut’s voice cannot reach the other (it is a vacuum).
(b) They use radio sets in their helmets. Radio waves are electromagnetic waves, like light, and can travel through vacuum.
Marking: (a) 1 mark (no air / vacuum, sound needs a medium); (b) 1 mark.
📖 Review this on Page 6 · Astronauts, Fig 8.12 · Page 11 · Let us assess Q6
💡 Think of the shape of the vibration – orderly or jumbled?
(a) Music (സംഗീതം) is produced by regular (orderly) vibrations and is pleasant to hear. Noise (ഒച്ച) is produced by irregular vibrations and is unpleasant.
(b) Music: a veena, a flute, a song in the music class. Noise: horns at a traffic junction, a construction drill, rubbing a coconut shell on a stone.
Marking: (a) 1 mark; (b) ½ + ½.
📖 Review this on Page 9 · Key box 8
💡 Compare 3 × 10⁸ m/s with 350 m/s.
Light travels at about 3 × 108 m/s, so the flash reaches us almost instantly. Sound travels in air at only about 350 m/s, so the thunder takes several seconds to cover the same distance (about 3 s for every kilometre).
Marking: 1 mark for comparing the two speeds, 1 mark for the conclusion.
📖 Review this on Page 7 · Thunder question · Page 4 · Light vs sound
💡 Think of the classroom, the road and the playground.
Difficulties: problems in communicating with others; risk of accidents (they may not hear horns or alarms); difficulty in learning in class; loneliness.
Support: treat them with sympathy and kindness; include them in every activity; speak facing them, clearly and a little slowly; learn some sign language; use written notes.
Marking: ½ mark for each of the four points.
📖 Review this on Page 8 · Hearing impairment, World Hearing Day
💡 What carries the sound from the bell to the glass and to us?
(a) The sound becomes fainter and fainter as the air is removed.
(b) We can still see the hammer striking (light travels through vacuum), but we can hardly hear anything. Let the air back in and the sound returns.
(c) Sound needs a medium (മാധ്യമം) to travel; it cannot travel through vacuum (ശൂന്യത).
Marking: 1 mark for each part.
📖 Review this on Page 6 · Buzzer in a jar, key box 4 · Page 11 · Let us assess Q10
| Instrument | Main vibrating part | One associated part that vibrates |
|---|---|---|
| Violin | (i) ………… | (ii) ………… |
| Elathalam | (iii) ………… | (iv) ………… |
| Tabla | (v) ………… | (vi) ………… |
💡 What do you pluck, clash or strike? What else vibrates with it?
| Instrument | Main vibrating part | Associated part |
|---|---|---|
| Violin | (i) the strings | (ii) the wooden body (or the bridge, or the air inside) |
| Elathalam | (iii) the metal plates | (iv) the air around them |
| Tabla | (v) the stretched skin (membrane) | (vi) the wooden body or the air inside |
The main part makes the vibration; the associated parts vibrate with it and make the sound sweeter and louder (key box 3).
Marking: ½ mark for each blank.
📖 Review this on Page 5 · Table 8.1, key box 3
💡 time = distance ÷ speed, once for each medium.
Given: distance d = 2972 m; speed in steel = 5944 m/s
Formula: time = distance ÷ speed
Substitution: 2972 ÷ 5944
Answer: (a) t = 0.5 s
Given: d = 2972 m; speed in air = 347 m/s
Formula: time = distance ÷ speed
Substitution: 2972 ÷ 347
Answer: (b) t ≈ 8.6 s
(c) She hears two sounds: first the one through the steel (solids carry sound fastest), and about 8.6 − 0.5 ≈ 8.1 s later the one through the air.
Marking: (a) 1 mark; (b) 1 mark; (c) ½ for “two”, ½ for “through steel first”.
📖 Review this on Page 7 · Table 8.3, medium race · Page 4 · time = distance ÷ speed
💡 Where are the air particles crowded, and where are they spread out?
(a) C – compression, a region of higher pressure (മർദം കൂടിയ മേഖല) where the air particles are crowded; R – rarefaction, a region of lower pressure (മർദം കുറഞ്ഞ മേഖല) where they are spread out.
(b) 1 – outer ear (pinna, ചെവിക്കുട); 2 – ear canal (കർണ്ണനാളം); 3 – eardrum (കർണ്ണപുടം).
(c) A source of sound, a medium and an organ of hearing (the ear).
Marking: (a) ½ + ½; (b) 1 mark for all three (two correct: ½); (c) 1 mark.
📖 Review this on Page 8 · Fig 8.15, key box 7 · Page 3 · Compressions and rarefactions
💡 distance = speed × time for the sound; time = distance ÷ speed for the light.
(a) Both happen together, but light (3 × 108 m/s) reaches her almost at once while sound (350 m/s) takes 6 s.
Given: v = 350 m/s; t = 6 s
Formula: distance = speed × time
Substitution: 350 × 6
Answer: (b) 2100 m = 2.1 km
Given: d = 2100 m; speed of light = 3 × 108 m/s
Formula: time = distance ÷ speed
Substitution: 2100 ÷ (3 × 108)
Answer: (c) 7 × 10−6 s (7 millionths of a second – “at once”)
(d) A shorter gap means a shorter distance: the storm is coming nearer. New distance = 350 × 3 = 1050 m.
(e) Go indoors at once (a building or a closed vehicle); keep away from tall trees, open grounds, terraces and water; do not use wired phones or touch electrical appliances; stay inside for 30 minutes after the last thunder (any two).
Marking: 1 mark for each part ((b), (c): formula ½, answer with unit ½; (d): ½ + ½; (e): ½ + ½).
📖 Review this on Page 7 · Thunder timer · Page 4 · Light vs sound · Page 12 · Thunderstorm lab
💡 Think of a busy junction, a festival loudspeaker and a hospital next to a road.
(a) Noise pollution (ശബ്ദമലിനീകരണം) is unnecessary sound that is unbearable and uncomfortable and that harms humans and other living things.
(b) The growing number of vehicles and their horns; loudspeakers and public-address systems; construction machines; factories; firecrackers; aircraft and trains.
(c) Headache, sleeplessness, stress and anger, high blood pressure, hearing loss, poor concentration in studies.
(d) Traffic police; workers in factories, mines and construction sites; people living near airports, highways and railway lines; patients in hospitals; babies, old people and students.
(e) No air horns, and silencers kept in good order; box-type loudspeakers instead of horn-type; no loudspeakers in public places before 6 am and after 10 pm; silence near hospitals, schools and courts; plant trees; ear plugs or ear muffs for workers near loud machines.
Marking: 1 mark for each part (½ for each point in (b)–(e)).
📖 Review this on Page 9 · Noise pollution, key box 9 · Page 12 · Noise-barrier lab
Marks summary
| Section | Questions | Marks each | Total | Topics |
|---|---|---|---|---|
| A | 1–8 | 1 | 8 | vibration, vacuum, Table 8.3, flute’s air column, vocal cords, eardrum, membrane instruments, Resul Pookutty |
| B | 9–13 | 2 | 10 | firecracker distance, astronauts on the Moon, music and noise, lightning before thunder, hearing loss |
| C | 14–17 | 3 | 12 | bell jar and vacuum pump, Table 8.1 (main and associated parts), steel vs air timing, compressions and the ear |
| D | 18–19 | 5 | 10 | thunderstorm distance and lightning safety, noise pollution |
| Total | 40 | |||
- Cool-off (15 min) – read the whole paper. Mark the three numericals (Q9, Q16, Q18) and note which speed each one gives you.
- Section A – about 10 minutes. One word or one letter; give the reason in Q7.
- Section B – about 20 minutes. For Q9 write Given, Formula, Substitution, Answer. In Q10 and Q12 use the words medium, vacuum and the two speeds.
- Section C – about 25 minutes. Fill every blank of the table in Q15; in Q16 show both divisions with units.
- Section D – about 25 minutes. Answer every part (a)–(e); two points each where two are asked.
- Checking – keep 10 minutes: units (m, s, m/s)? time = distance ÷ speed, not speed ÷ distance? “cannot travel through vacuum”?
Count your marks: 32 or more – excellent; 24–31 – good, revise the pages linked under the questions you missed; below 24 – go back through pages 5, 6, 7, 8 and 9 with their labs and do the scored quiz again. Then return to the chapter home and tick off what you have learned.