1. Answer the following
(a) Why does friction cause a charge to develop?
Ans: (1) Friction takes place between two substances.
(2) Every substance is made up of matter.
(3) Substances are charge less because of equal number of opposite charges on them.
(4) Due to friction, negative charge gets transferred from one substance to another.
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Classification of Substances
EXERCISES
1. Write the answers to the following questions.
(a) How are properties of substances determined?
(b) Explain the differences between compounds and mixtures
(c) Why is an alloy a mixture?
(d) Why are substances classified?
2. Fill in the blanks.
(a) In a compound the ………………. do not retain their properties.
1. Write answers to the following questions.
(a) Why do we hear musical notes when strings of a sitar are plucked?
(b) How does a bat find its way in the dark?
(c) What is the SONAR system based on?
(d) Why is the sound of the bell smothered when a hand is placed on it?
2. Fill in the blanks.
(a) Man can hear sounds of sound frequencies between 20 and …………… Hz.
(b) Amplitude and …………….. are not related.
1. Answer the following
(a) Give a simple experiment to show that a medium is necessary for the propagation of sound.
(b) How is sound produced in drums?
(c) What is a noise?
2. Give reasons:
(a) A table player tightens or loosens the bands tying down the membrane.
(b) We hear thunder long after we have seen the flash of lightning.
1. Answer the following questions:
(a) What is meant by autotrophic living things?
ANS: (1) Living things need food to survive.
(2) Some living things can make their own food. They are called autotrophs. Example: Plants make their own food with the help of sunlight.
(b) What is a balanced diet?
ANS: (1) All living things need food for growth and to repair the wear and tear of their bodies.
(2) For good nourishment, it is important that carbohydrates, proteins, fats as well as minerals and vitamins are provided in proper proportion.
Propagation of light from vishnumestry29
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FOOD AND PROTECTION OF FOOD
1. Write answers to the following questions.
a) Name the constituents of food and give five examples of each.
ANS: The constituents of food are,
Carbohydrates – Rice, Wheat, Jowar, Bajra, corn etc
Proteins – Pulses, legumes, eggs, fish, meat ets
Fats – Butter, oil, margarine, cream, ghee etc
Minerals – Sodium, potassium, calcium, iron, phosphorus.
Vitamins – Vitamin A, Vitamin B, Vitamin C, Vitamin D, Vitamin E.
b) Name some fibrous foods.
