Question

9. A 20 mm tall object is placed perpendicular to the principal
axis of a convex lens of focal length 10 cm. If the distance of the
object from the lens is 15 cm, then-​

Answer 1

Explanation:

7th

Maths

Perimeter and Area

Perimeter and Area of a Circle

A semicircle is drawn with ...

MATHS

A semicircle is drawn with AB as its diameter. From C a point on AB a line perpendicular to AB is drawn meeting the circumference of the semicircle at D. Given that AC=2 cm and CD=6 cm the area of the semicircle is :

MEDIUM

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ANSWER

Let O be the centre of the circle. Then, OA=OB=OD=r

Now, OC=r−2

and CD=6

Thus, in △ODC

OC

2

+CD

2

=OD

2

(r−2)

2

+6

2

=r

2

r

2

+4−4r+36=r

2

4r=40

r=10 cm

Area of semicircle =

2

πr

2

=

2

π(10)

2

=50π

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