(4) কোনাে একটি দ্রব্যের দাম প্রথমে 15 % হ্রাস করা হল। তারপর আবার 20% হ্রাস করা হল । তাহলে মােট
দামের শতকরা পরিবর্তন কত হবে? – (a) 25 % হ্রাস (b) 32 % হ্রাস (c) 35 % হ্রাস (d) 68 % হ্রাস
(5) কোনাে একটি দ্রব্যের ওপর যথাক্রমে 10% এবং 10% হারে দাম বৃদ্ধি করা হয়। তাহলে দ্রব্যটির ওপর সমতুল্য
দাম বৃদ্ধি কত হবে?– (a) 19 % (b) 20 % (c) 21% (d) 22 %
Answers
1. Why should magnesium ribbon be cleaned before burning in air?14. Identify the device used as a spherical mirror or lens in following cases, when the image formed is virtual
and erect in each case.
(a) Object is placed between device and its focus, image formed is enlarged and behind it.
(b) Object is placed between the focus and device, image formed is enlarged and on the same side as
that of the object.
(c) Object is placed between infinity and device, image formed is diminished and between focus and
optical centre on the same side as that of the object.
(d) Object is placed between infinity and device, image formed is diminished and between pole and
focus, behind it.17. A Converging lens and diverging lens of focal length 50cm and 100 cm are combined together. Find the
Power and focal length of the combined lens.1. Why should magnesium ribbon be cleaned before burning in air?14. Identify the device used as a spherical mirror or lens in following cases, when the image formed is virtual
and erect in each case.
(a) Object is placed between device and its focus, image formed is enlarged and behind it.
(b) Object is placed between the focus and device, image formed is enlarged and on the same side as
that of the object.
(c) Object is placed between infinity and device, image formed is diminished and between focus and
optical centre on the same side as that of the object.
(d) Object is placed between infinity and device, image formed is diminished and between pole and
focus, behind it.
Step-by-step explanation:
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