Class 8th Science Chapter 8 Measurement of Physical Quantities

Class 8th Science Chapter 8 Measurement of Physical Quantities

Class 8th Science Chapter 8 Measurement of Physical Quantities. Measurements of physical quantities are expressed in terms of units, which are standardized values. For example, the length of a race, which is a physical quantity, can be expressed in units of meters (for sprinters) or kilometres (for distance runners).

Class 8th Science Chapter 8 Measurement of Physical Quantities
Class 8th Science Chapter 8 Measurement of Physical Quantities 6

Class 8th Science Chapter 8 Measurement of Physical Quantities

Class 8th Science Chapter 8 Measurement of Physical Quantities. A physical quantity is a property of a material or system that can be quantified by measurement. A physical quantity can be expressed as a value, which is the algebraic multiplication of a numerical value and a unit. For example, the physical quantity mass can be quantified as n kg, where n is the numerical value and kg is the unit.

 Class 8th Science Chapter 8 Measurement of Physical Quantities
Class 8th Science Chapter 8 Measurement of Physical Quantities 7

A physical quantity has at least two characteristics in common. One is the numerical magnitude and the other is the unit in which it is measured. Class 8th Science Chapter 8 Measurement of Physical Quantities

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Q1. Write seven base physical quantities along with their SI units.

Ans:

Quantity

Unit

Symbol

Length

Meter

m

Mass

Kilogram

kg

Time

Second

s

Temperature

Kelvin

K

Electric current

Ampere

A

Intensity of light

Candela

cd

Amount of substance

Mole

mol

Q2. Write the uses of units in our daily life.

Ans: We use units in our daily life to measure length, mass, time, temperature, electric current, intensity of light and amount of substance.

Q3. Why scientists prefer SI units?

Ans. Scientists prefer SI units to exchange their scientific research and information with world’s scientific community.

Q4. Convert 1000 centimeters into meters and millimeters.

Ans. ­ 1 cm ₌ 1/100 m

1000 cm ₌ 1000/100 m ₌ 10 meters

1 cm ₌ 10 millimeters

1000 cm ₌ 10 x 1000mm

10000 mm

Q5. Physical quantities are divided in how many categories?

Ans. Physical quantities are divided in two main categories.

1). Base quantities.

These are fundamental physical quantities. Other physical quantities are derived from them.

2). Derived quantities: These are physical quantities which are derived from the base quantities by multiplication or division or both

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Q1. What are international system units? How they are used in daily life?

Ans: The international system units are the set of physical units agreed upon by international convention and accepted as a standard for all the measurements in the world. The SI units are sometimes called MKS units, where MKS stands for meter, kilogram, and second. SI units based on meter, kilogram, second, ampere, Kelvin, candela, and mole with a set of prefixes to indicate multiplication or division by a power of 10.

Use of SI units in daily life

SI units are used in our daily life to measure length, mass, time, temperature, electric current, intensity of light and amount of substance.

Q2. (A). what is meniscus?

Ans. Meniscus is the curve seen at the top of a liquid in response to its container. It has two types.

Concave meniscus: Concave meniscus is formed when the molecules of a liquid are more attracted to the container.

Convex meniscus: Convex meniscus is formed when the molecules of a liquid are more attracted to each other.

(b). Give in detail the procedure of measuring the volume of liquid by reading correct meniscus in the measuring cylinder.

Ans: For correct measurement of the volume, the cylinder must be placed on horizontal surface and the eye should be kept on a level with the bottom of the meniscus.

Q3. What are prefixes? Explain their role in System international units.

Ans. Prefixes are words or letters used before SI units to express very large or small quantities. Some of the prefixes are mille, centi, kilo etc. The value of these prefixes is the multiples and sub-multiples of 10.

Role of prefixes in SI units

Prefixes are used for the inter conversion of smaller units and bigger units.

Examples: Kilo increases the value of a unit by 1000. Centi decreases the value of a unit by 1/100. Mille decreases the value of a unit by 1/1000.

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