Students of a school staged a rally for cleanliness campaign. They walked through the lanes in two groups. One group walked through the lanes AB, BC and CA; while the other through AC, CD and DA (see Fig. 12.12). Then they cleaned the area enclos

Students of a school staged a rally for cleanliness compaign. They walked through the lanes in two groups. One group walked through the lanes A B , B C a n d C A ; while other through A C , C D a n d D A (See in Figure). Then they cleaned the ara enclosed within their lanes. If A B=9m B C=40 m , C D=15 m , D A=28 m , a n d /_B=90^0dot Which group cleaned more area and by how much? Find the total area cleaned by the students.

A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample contained in a beaker/tumbler in the box as shown in the Figure. They were amazed to see that milk taken in the tumbler was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it ? (a) Explain why the milk sample was illuminated? Name the phenomenon involved. (b) Same results were not observed with a salt solution. Explain. (c) Can you suggest two more solutions which would show the same effect as shown by the milk solution?

For the cuboid shown in figure,the lengths of AB, BC, CG are 12, 8, 6 units respectively. Two points P and Q are chosen such that they are the mid-points of the edges GH and CD respectively. Two cuts are then made using a knife so as to cut the cuboid in to three pieces. The first cut passes through PQ to meet EA. The second cut is made on other side of PQ to meet FB. The difference in the total surface area (in square units) of the biggest of the three new pieces and the total surface area of initial cuboid is :