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NCERT Solutions for Class 4th Maths Chapter 1 Making a right angle checker and using it — Right Angles

Book page 11 Updated on2026-09-19

Q1.
Where do you see angles in the classroom? Give a few examples.
Answer

Angles are everywhere — look for two straight edges that meet.

  • The corner of the blackboard, where two edges meet.
  • The corner of your notebook and of the desk top.
  • The open door and the wall beside it.
  • The two hands of the wall clock.
  • The corner of a window, and where the wall meets the floor.
  • An open book, at its spine.
  • The legs of a chair where they meet the seat.
Sample answer: I see angles at the corners of the blackboard, at the corners of my desk, between the hands of the clock and between the open door and the wall.
Why it happens: Wherever two straight things meet at a point, an angle is made. Classroom things are mostly made of straight edges, so angles are all around us.
Q2.
Let’s make a right angle with a piece of paper as shown.
→this corner is a right angle
Folding a piece of paper twice to make a right angle checker.
Answer

Fold once, then fold again — and the corner you get is a right angle.

  1. Take any piece of paper. Its edges need not be straight.
  2. Fold it in half and press the fold flat.
  3. Now fold it again, bringing the folded edge exactly on top of itself.
  4. Open it a little. The corner where the two folds meet is a right angle.

This folded paper is your right angle checker. Put its corner on any corner you want to test. If the two edges lie exactly along the paper, that corner is a right angle.

Why it happens: The first fold makes a straight edge. The second fold cuts that straight edge into two equal parts, and a straight edge cut into two equal parts gives two right angles.
Q3.
Identify the angles that you think are right angles and circle them in the dot grid given below. Check using your right angle checker.
The eight angles drawn on the dot grid in the book.
Answer

Four of the eight angles are right angles.

Going along the grid, the right angles are:

  • the second angle in the top row — one arm goes left, the other goes straight down;
  • the third angle in the top row — one arm goes straight up, the other goes right;
  • the first angle in the bottom row — the two arms slope equally, one up and one down;
  • the last angle in the bottom row — again two equal slopes, one up and one down.

The other four are not right angles: the first and the fourth in the top row are wider than the checker (obtuse), and the two middle ones in the bottom row are narrower than the checker (acute).

The same eight angles, with the right angles ringed.
Why it happens: A right angle is the corner of a square, so on a dot grid it appears either as one arm across and one arm straight down, or as two arms sloping by the same amount on opposite sides.
Q4.
Check for right angles in a book, window, and any other object. Write the names of objects where you find right angles.
Answer

Press the corner of your folded paper on each corner and see if it fits exactly.

Objects with right angles

  • the four corners of a book and of a notebook;
  • the corners of a window and of a door;
  • the corners of the blackboard, a table top and a chart paper;
  • the corners of a brick, a chalk box and a tile on the floor;
  • the corner of a set square, a postcard and a stamp.
Sample answer: I found right angles in my book, the window, the blackboard, the table top and the floor tiles.
Why it happens: Most things we make are rectangles, and every corner of a rectangle is a right angle. That is why right angles are so easy to find.
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