CHAPTER: Physical Quantities Class 7

1. What are Physical Quantities?

Ans: Mesearurable quantities are called Physical Quantities.

Ex- length

2. What is Measurement?

Ans: To find out the exact value of a quantity we use a procedure that is called Measurement.

3. How many types of physical quantities?

Ans: Two types of Physical Quantities - Fundamental Quantity and Derived Quantity.

4. Define Fundamental Quantity.

Ans: Fundamental quantities are unique, they do not depend on others.

Ex- length - metre, time - second.

5. Define Derived Quantity.

Ans: Derived Quantities depend on other fundamental quantities.

Ex- speed = distance/ time

= metre/ second

6. Define non-standard units.

Ans: Different body parts were used to measure the substance in earlier times are called non-standard units.

Ex- Cubit, Handspan, Footspan.

7. What is a Unit?

Ans: Physical quantity measure with known fixed quantity.

Ex- length - metre ( m )

8. Write some names of devices that measure length.

Ans: i) Ruler

ii) Vernier Callipers

iii) Measuring tape

9. Write some S.I. units with symbols.

Ans: length - metre ( m ),

mass - kilogram ( kg ),

temperature - kelvin ( k ),

electric current - ampere ( A ),

time - second ( s ),

luminous intensity - candela ( cd ),

10. What is parallax error?

Ans: Incorrect position of eyes to measure a reading is called parallax error.

11. How do you correct parallax error?

Ans: Keep your eyes on the point perpendicularly.

12. How do you measure the thickness of a page of your physics book?

Ans: Thickness of a page = total thickness of the book / total number of pages.

13. How do you measure your hair?

Ans: Diameter of the hair = total length of the turns of the hair / number of turns of hair.

14. Define area. Write the S.I. unit of area.

Ans: The amount of closed figure on plane surface is called area.

S.I. unit of area is square metre ( or m² or sq metre )

15. How do you find the area of the usual surface or figure?

Ans: Triangle - 1/2 × base × height

Circle - πr²

Rectangle - length × breadth

16 . How do you find the area of unusual figure?

Ans: We can find the area of unusual figure by graph paper.

17. Define mass. S.I. unit of mass.

Ans: How many matters are present in a substance is called mass.

S.I. unit of mass is 'kilogram'.

18. Write the name of the devices to measure the mass.

Ans: Beam balance, Electronic balance.

19. Define volume. S.I. Unit of volume.

Ans: The amount of space occupied by the substance is called volume.

S.I. Unit of volume - cubic metre ( m3 )

20. Which devices are used to measure volume?

Ans: Measuring cylinder, Measuring beaker.

21. Define Meniscus? Give an example.

Ans: Curved surface of liquid in a cylinder is called Meniscus.

Water - concave meniscus ( lower curved )

Mercury - convex meniscus ( upper curved )

22. How do you find the volume of the usual figure?

Ans: Sphere - 4/3 πr

Cylinder - πr²h

Cuboid - length × breath × height

23. i) 1 litre = ____ ml ii) 1 litre = _____ cm3

Ans: i) 1000 ml ii) 1000 cm3

24. How do you measure the volume of an unusual substance?

Ans: We can measure the volume of unusual substances by water displacement

process through measuring cylinder.

25. What is density? Write the S.I. unit of density.

Ans: The ratio between mass and volume is called density.

The S.I. unit of density is gm / cm3

26. When the density of water is maximum?

Ans: At 4℃ water density is maximum. ( 1gm / cm3 )

27. What is temperature?

Ans: Temperature is the hotness or coldness of a body.

S.I. Unit of Temperature is kelvin ( K ), the other two common Units are degree Celsius ( ℃ ) and degree Fahrenheit ( ℉ ).

28. Which device is used to measure temperature?

Ans: A thermometer is used to measure temperature. ( Clinical Thermometer and Laboratory Thermometer ).

29. Write the difference between a clinical thermometer and a laboratory thermometer.

Ans:

Clinical Thermometer	Laboratory Thermometer
i) Measure body temperature	Measure room temperature
ii) Has kink	Has no kink
iii) Range 35 ℃ to 42℃	Range -10℃ to 110℃

30. What is the function of kink?

Ans: The kink prevents the mercury to back into the bulb.

31. What is the relation between the Centigrade and Fahrenheit scales.

Ans:

32. Which liquid is used in thermometers?

Ans: Mercury is used in thermometers.

33. Why mercury is used in thermometers?

Ans: i) it is always in pure form.

ii) it is shiny and nonsticky so easily visible.

iii) good conductor heat with a wide range -39℃ to 357℃

34. What is the normal body temperature of a human?

Ans: 37 ℃ or 98. 6 ℉

35. What is the use of maximum and minimum thermometers?

Ans: It is used to find the maximum and minimum temperature of a particular day place.

36. Which devices are used to measure time?

Ans: i) Earlier time - Sundial, Sand clock.

ii) Nowadays - Digital watch, Analogue watch.

37. How many clock systems are used?

Ans: i) 12-hour clock system -

7:30 am ( it means morning ), 7:30 pm ( it means evening )

ii) 24-hour clock system -

00:00 hours ( midnight ), 07:30 hours ( morning ),

12:00 hours ( noon ), 19.30 hours ( evening )

38. Write the full form of am. and pm.

Ans: am - Ante meridien

pm - post meridien

39. What is speed? S.I. unit of speed.

Ans: How much distance is covered in a particular time is called speed.

S.I. unit of speed is m / s

40. What is the average speed?

Ans: The average speed = total distance / total time taken

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