Q35 of 805 Page 169

Why do some children fall ill more frequently than others living in the same locality?

OR


Give any four factors necessary for a healthy person.

Following can be the reasons for some children falling ill as compared to others living in the same locality-


(a) Lack of balanced diet


(b) Unavailability of clean drinking water


(c) Poor hygiene


(d) Absence of vaccination


(e) Less developed immune system


OR


(a) The surrounding environment should be clean. Air and water-borne diseases should not spread.


(b) Personal hygiene prevents infectious diseases.


(c) Proper, sufficient nourishment and food is necessary for good immune system of our body.


(d) Immunization against severe diseases.


More from this chapter

All 805 →
33

An Italian bee variety Apis mellifera has been introduced in India for honey production. Write about its merits on other varieties.

 34

A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the sample taken in a beaker/glass tumbler as shown in the figure. They were amazed to see that milk taken in the glass was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it


(a) Explain why the milk sample was illuminated. Name the phenomenon involved.


(b) Same results were not observed with a salt solution. Explain.


(c) Can you suggest two more solutions which would show the same effect as shown by the milk solution?


OR


During an experiment the students were asked to prepare a 10% solution of sugar in water. Ramesh dissolved 10g of sugar in 100g of water while Sarika prepared it by dissolving 10g of sugar in water to make 100g of the solution.


(a) Are the two solutions of the same concentration?


(b) Compare the mass % of the two solutions.

 36

Define power. How will you differentiate between kW and kW h? If the velocity of a ball is tripled, what will be the ratio of

(a) its initial kinetic energy and final kinetic energy


(b) initial momentum and final momentum.


OR


Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it.


(a) How much work the men do in lifting the box?


(b) How much work do they do in just holding it?


(c) Why do they get tired while holding it? (g = 10 m s–2)

 37

(a) Explain how ‘echo’ is produced.

(b) What should be the minimum distance between the listener and the reflector to hear an echo of sound propagating with a speed v m s–1?


(c) Does the speed of sound increase or decrease on a hotter day? Justify.


OR


Establish the relationship between speed of sound, its wavelength and frequency. If speed of sound in air is 340 m s–1, calculate.


(a) wavelength when frequency is 256 Hz.


(b) frequency when wavelength is 0.85 m.