Measurement Online Test 7th Science Lesson 1 Questions in English

In day-to-day life, we measure many things such as the weight of fruits, vegetables, food grains, volume of liquids, temperature of the body, speed of the vehicles etc., Quantities such as mass, weight, distance, temperature, volume are called physical quantities.

Generally, physical quantities are classified into two types, namely, (i) Fundamental quantities and (ii) Derived quantities.

A set of physical quantities which cannot be expressed in terms of any other quantities are known as “Fundamental quantities”. Their corresponding units are called “Fundamental units”.
All other physical quantities which can be obtained by multiplying, dividing or by mathematically combining the fundamental quantities are known as “derived quantities”. Their corresponding units are called “Derived units”.

The area is a measure of how much space there is on a flat surface. The area of the plot of land is derived by multiplying the length and breadth
Area = length × breadth
The unit of the area is = metre × metre
= metre2
= m2 (Read as square metre).
Area is a derived quantity as we obtain are by multiplying twice of the fundamental physical quantity length

Length – Metre (m); Mass – Kilogram (kg); Time – Second (s); Temperature – Kelvin (K); Electric current – Ampere (A); Amount of substance – Mole (Mol); Luminous (light) intensity – Candela (cd).

Area = length × breadth – m × m = square metre (or) m2; Volume = length × breadth × height – m × m × m = cubic metre (or) m3; Speed = distance / time – m / s (or) m s-1; Electric charge = electric current × time – A × s = As (or) Coulomb (C); Density = mass / volume – Kg / m3 (or) kg m-3.

Area of a square = side × side
= 1 m × 1 m = 1 m2 or 1 square metre
Area of 10 squares = 1 square metre × 10
= 10 square metre
(Even though the area is given in square metre, the surface need not to be square in shape).

Square = side × side = a × a = a2; Rectangle = length x breadth = l x b=lb; Circle = π ×(radius)2 = π ×r2 =πr2; Triangle = (1/2) × base × height = 1/2 × b × h.

In our daily life, we encounter many irregularly shaped figures like leaves, maps, stickers of stars or flowers, peacock feather etc. The area of such irregularly shaped figures cannot be calculated using any formula. We can find the area of these figures with the help of a graph sheet.

(i) Area of rectangle = length × breadth = 12 × 4 = 48 m2
(ii) Area of circle = π × r2 = (22/7) × 7 × 7 = 154 m2
(iii) Area of triangle = (1/2) × base × height = (1/2) × 6 × 8 = 24 m2

The amount of space occupied by a three-dimensional object is known as its volume. volume = surface area × height.

The SI unit of volume is cubic metre or m3. As in the case of area, the volume of the regularly shaped objects can also be determined using an appropriate formula.

The volume of Cuboid is length × breadth × height = l × b × h = l b h.

(i) Volume of a cube = side × side × side = 3 cm × 3 cm × 3 cm = 27 cubic cm or cm3.
(b) Volume of a cylinder = π × r2 × height = (22/7) × 3 × 3 × 7 = 198 m3

The volume of cylinder is π × (radius)2 × height = π ×r2 ×h = π r2 h.

The volume of the sphere is 4/3 × π × (radius)3 = 4/3 × π ×r3 = 43 π r3.

To understand this unit of volume, let us first understand how much a litre means. Litre is the commonly used unit to measure the volume of liquids. we can understand that the unit of volume is cubic cm if the dimensions of the object are given in cm. This cubic cm is commonly known as cc. A volume of 1000 cc is termed as one litre (l). 1 litre = 1000 cc or cm3 1000 ml = 1 litre.

To measure the volume of liquids, some other units are also used. Some of them are gallon, ounce, and quart.

1 gallon = 3785 ml.

Density of a substance is defined as the mass of the substance contained in unit volume (1 m3).

If the mass of a substance is “M” whose volume is “V”, then, the equation for density is given as
Density (D) = mass (M)volume (V) = MV

The SI unit of density is kg/m3.

The CGS unit of density is g/cm3.

Different materials have different densities. The materials with higher density are called “denser” and the materials with lower density are called “rarer”.

Air – 1.2 kg/m3, Kerosene – 800 kg/m3, Water – 1000 kg/m3, mercury – 13600 kg/m3.

The density of wood is 770 kg/m3.

Iron – 7800 kg/m3, Copper – 8900 kg/m3, Silver – 10500 kg/m3, Gold – 19300 kg/m3.

Density of cylinder = mass of cylinder volume of cylinder = 2804 = 70 Kg/m3.

Density = Mass / Volume
Hence, Mass = Volume × Density = 125 × 7.8 = 975 g.

Density = Mass/ Volume
Mass = Density × Volume
Volume = Mass / Density

Density = Mass / Volume
Hence, Volume = Mass / Density
= 3000 / 8900 = 30 / 89 = 0.34 m3.

Normally, we use centimetre, metre and kilo metre to express the distances that we measure in our day-to-day life. But, for space research, astronomers need to measure very long distances such as the distance between the earth and a star or the distance between two stars. To express these distances, we shall learn about two such units, namely, i. Astronomical unit ii. Light year.

Water has more density than oils like cooking oil and castor oil, although these oils appear to be denser than water. Density of castor oil is 961 kg/m3. If we put one drop of water in oil, water drop sinks. But, if we put one drop of oil in water, oil floats and forms a layer on water surface. However, some oils are denser than water.

We all know that the earth revolves around the sun in an elliptical orbit. Hence, the distance between the sun and the earth varies every day. Perihelion is position of the shortest distance between the earth and the sun.

When the earth is in its perihelion position (Perihelion is position of the shortest distance between the earth and the sun), the distance between the earth and the sun is about 147.1 million kilometres.

When the earth is in its farthest position, that is when the distance between Earth and Sun is the largest it is called aphelion position.

When the earth is in its farthest position, that is when the distance between Earth and Sun is the largest (called aphelion position) the distance is 152.1 million kilometres.

The average distance between the earth and the sun is about 149.6 million kilometres. Th is average distance is taken as one astronomical unit. One astronomical unit is defi ned as the average distance between the earth and the sun.

Neptune is 30 AU away from the Sun. It means it is thirty times farther than the Earth.

The nearest star to our solar system is Proxima Centauri. It is at a distance of 2,68,770 AU.

We can clearly see that using the AU for measuring distances of stars would be unwieldy. Therefore, astronomers use a special unit, called ‘light year’, for measuring the distance in deep space. One light year is defined as the distance travelled by light in vacuum during the period of one year.

We, have learnt that the speed of light in vacuum is 3 × 108 m/s. Th is means that light travels a distance of 3 × 108 m in one second.

In a year (non-leap), there are 365 days. Each day has 24 hours; Each hour has 60 minutes; Each minute has 60 seconds. Th us, the total number of seconds in one year = 365 × 24 × 60 × 60 = 3.153 × 107 second.
If light travels a distance of 3 × 108 m in one second, then the distance travelled by light in one year = 3 × 108 × 3.153 × 107 = 9.46 × 1015 m. This distance is known as one light year.
1 Light year = 9.46 × 1015 m.

In terms of light year, Proxima Centauri is at 4.22 light-years from Earth and the Solar System (and Earth).

The Earth is located about 25,000 light-years away from the galactic centre.

1 ounce = 30 ml; 1 quart = 1 litre