13. Define 1 kilogram,the S .I. unit of mass
How is it related to a) quintal b) metric ton and c) gram ?
Ans. In in 1889 , 1 kilogram was defined as the mass of a cylinder of platinum iridium alloy kept at the International Bureau of weights and measures at sevres near Paris.
Or
At present, the mass of one litre (=1000 ml) of water at 4 degree celsius is taken as 1 kilogram.
1 quintal=100kg
1 metric ton=1000 kg
1g = 10‐³ kg
14. Name and define the SI unit of time. How is it related to a)minute b) hour c) day and d)year ?
Ans. SI unit of time is second.
1 second is defined as (1/86400 ) th part of a mean solar day. i.e.,
1s =1/86400 × one mean solar day.
a) 1 minute= 60 s
b) 1 h = 60 minutes
=60×1 minute
=60×60 s (1 minute=60 s)
=3600 s
c) 1day= 24 hours
=24×1h
=24×3600 s (1h=3600s)
=86400 s
d) 1 year=365 days
=365×1 day
=365×86400 s (1day=86400s)
=31536000 s
=3.1536000 × 10⁷ s
=3.15 × 10⁷ s
15. Name two devices used to measure the short time interval of an event.
Ans. The two devices used to measure the short time interval of an event are:
1. Stop clock
2. Stop watch
3. Electronic stopwatch
16. Express in second
a)3 minute 15 second
b)5 hour 2 minute 5 second
Ans. a) 3 minute 15 second
=3× 1 minute + 15 s
=3×60 s + 15 s (1 minute=60 s)
= 180 s + 15 s
= 195 s
b)5 hour 2 minute 5 second
=5×1h +2×1 minute +5 s
=5×60×60 s +2× 60 s + 5s (1h=60 minute,1minute=60s , so 1h=60×60 s)
=18000 s + 120 s + 5 s
=18125 s
17. What does the temperature measure?
Ans. The temperature measures the degree of hotness or coldness of an object.
18. Name the SI unit and one common unit of Temperature. Write their symbols also.
Ans. SI unit of Temperature is Kelvin.
Symbol is K.
Other unit of Temperature are degree Celsius and degree fahrenheit.
Their symbols are °C & °F respectively.
19. Name the instrument used for measuring the temperature of a person.Draw its level neat diagram.
Ans. The the instrument it used for measuring the temperature of a person is is clinical thermometer.
Draw fig.2.18 of your physics book.
21. Write the temperature of melting Ice and boiling water.
Ans. Temperature of Melting Ice is 0 degree Celsius.
Temperature of boiling water is 100 (hundred) degree Celsius.
21. What is a clinical thermometer ?state its special features. draw a neat diagram of a clinical thermometer showing the range of temperature marked on it.
Ans. Clinical thermometer is a special thermometer used by doctors to measure the temperature of the patient's body.
Draw fig.2.18 of your physics textbook.
A clinical thermometer has the markings from 35 degree celsius to 42 degree Celsius. It has a slight bend or kink in the stem just above the bulb. this kink is called construction. this construction prevents the Mercury from falling back all by itself. the temperature of a healthy person is 37 degree Celsius. this temperature is marked by a red arrow.
22. What is the normal temperature of the human body how is it indicated in a clinical thermometer metre ? Ans. Normal temperature of the human body is 37 degree Celsius. The normal temperature is indicated in a clinical thermometer by a red arrow on it.
23. Can a clinical thermometer be used to measure the temperature of the boiling water? Give reason for your answer.
Ans .a clinical thermometer cannot be used to measure the temperature of the boiling water. Because the maximum temperature which can be measured by a clinical thermometer is 42 degree Celsius.
24. Explain the term 'area of a surface'.
Ans. The total surface occupied by an object is called its surface area or simply the area.
25. Name the SI unit of area and define it.
Ans. SI unit of area is square metre.
Square metre is equal to the area of a square of side 1 metre.i.e.,
1m²=1m×1m.
26. How are the units a)square yard b)hectare c)km² d)cm² e)mm² related to the SI unit of area?
Ans.a) 1 square yard=1yard×1 yard
=0.9144 m×0.9144m
=0.836 m²
=0.84 m²
b)1 hectare=100m×100m
=10⁴ m²
c)1km²=1000m×1000m
=10⁶m²
d) 1 cm²=1/100 m × 1/100 m
=1/10000 m²
=10-⁴ m²
e) 1mm²=1mm×1mm
=10-³m ×10-³m
=10‐³-³ m²
=10‐⁶ m²
27. Explain how you will measure the area of a square and a leaf.
Ans. Area of a square can be calculated by formula method.
Area of a square= side× side. Draw fig.2.22 of your physics textbook.
Area of a leaf can be calculated by using graph paper (graphical method).
Approximate area=( number of complete square + number of half or more than half of incomplete square)×area of 1 square.
Draw fig.2.21 of your physics textbook & find its area .
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