Page 70 - Mathematics Class - X

Unit 5 Trigonometryy
Trigonometr

ACTIVITY 5.1

OBJECTIVE
To find the height of a building using a clinometer.

MATERIALS REQUIRED

Clinometer (a stand fitted with a square plate which is fitted with a movable 0° to 360° protractor and a straw)
A table or stool

A measuring tape 50 m long

PRE-REQUISITE KNOWLEDGE

1. Knowledge about clinometer
2. Trigonometric ratio (tan) for right-angled triangle

3. Understanding of the line of sight
4. Understanding of the angle of elevation and depression

THEORY

1. A clinometer is an instrument used to measure the angle of a slope.
Perpendicular
2. In a right-angled triangle, trigonometric ratio, tan q =
Base
where, side opposite to angle q is perpendicular and side adjacent to it, is base.
3. Line of sight: The line drawn from the eye of an observer to the point at the object viewed by the observer.

4. Angle of elevation: The angle formed by the line of sight with the horizontal, when it is above the horizontal
level, i.e. the case when we raise our head to look at the object (Fig. (a)).
5. Angle of depression: The angle formed by the line of sight with the horizontal, when it is below the
horizontal level, i.e. the case when we lower our head to look at the object (Fig. (b)).

Fig. (a) Fig. (b)

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