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Question
How wide is the rectangle? ________ cm
Solution
The breadth of a yellow rectangle is 8 cm.
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RELATED QUESTIONS
The principle of ‘parallax’ in section 2.3.1 is used in the determination of distances of very distant stars. The baseline AB is the line joining the Earth’s two locations six months apart in its orbit around the Sun. That is, the baseline is about the diameter of the Earth’s orbit ≈ 3 × 1011m. However, even the nearest stars are so distant that with such a long baseline, they show parallax only of the order of 1” (second) of arc or so. A parsec is a convenient unit of length on the astronomical scale. It is the distance of an object that will show a parallax of 1” (second) of arc from opposite ends of a baseline equal to the distance from the Earth to the Sun. How much is a parsec in terms of meters?
The nearest star to our solar system is 4.29 light years away. How much is this distance in terms of parsecs? How much parallax would this star (named Alpha Centauri) show when viewed from two locations of the Earth six months apart in its orbit around the Sun?
Match the following.
| Column A | Column B |
| (1) Length | a. kilogram |
| (2) Mass | b. cubic metre |
| (3) Area | c. metre |
| (4) Volume | d. square metre |
Exercise
While measuring the length of an object using a ruler, the position of your eye should be
A hand span is a reliable measure of length.
Match the following.
| 1. | Length | kelvin |
| 2. | Mass | metre |
| 3. | Time | kilogram |
| 4. | Temperature | second |
Can you find the diameter of a thin wire of length 2 m using the ruler from your instrument box?
Guess the lengths to draw these things. Ask your friend to draw the same. After you make the drawing use a scale to measure the length. Whose drawing showed a better guess?
| Guess its length and draw |
Measure of your drawing |
Measure of your friend’s drawing |
| An ant of length less than 1 cm |
||
| Pencil of length about 7 cm |
||
| A glass 11 cm high with water up to 5 cm |
||
| A bangle of perimeter 20 cm |
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| A curly hair of length 16 cm |
Which line is longer? C or D? Measure each line. How good is your guess?
Difference in size 
Do this for yourself and find the difference.
How many stamps are needed to cover the rectangle?
How close was your earlier guess? Discuss.
You can play this game on the ground. Make two squares of one square meter each. Divide your class into two teams. Ready to play!
- Which team could make more children stand in their square? How many?
Chumki, Jhumri, and Imran need wire to make a fence.
- How much wire in all will the three need?
So Anar also tried many different ways to make a boundary for 800 square meters of land.
He made rectangles A, B, and C of different sizes. Find out the length of the boundary of each. How much gold wire will he get for these rectangles?
- A
Gold wire for A = _________ metres - B
Gold wire for B = _________ metres - C
Gold wire for C = __________ metres
But then Anar made an even longer rectangle... See how long!
- D
So he will get __________ metres of gold wire!!
There are two beautiful lakes near a village. People come for boating and picnics in both the lakes. The village Panchayat is worried that with the noise of the boats the birds will stop coming. The Panchayat wants motorboats in only one lake. The other lake will be saved for the birds to make their nests.
- What is the length of the boundary of lake B in the drawing?
There are two beautiful lakes near a village. People come for boating and picnics in both the lakes. The village Panchayat is worried that with the noise of the boats the birds will stop coming. The Panchayat wants motorboats in only one lake. The other lake will be saved for the birds to make their nests.
- How many kilometers long is the actual boundary of lake B?
Larger unit for measuring time is ______.
The distance of a galaxy is of the order of 1025 m. Calculate the order of magnitude of time taken by light to reach us from the galaxy.
