In a classroom , 4 friends are seated at the points A,B,C and D as shown in Figure . Champa and Chameli walk into the class and after observing for a new minutes Champa asks Chameli , "Don't you think ABCD is a square ?" Chameli disagrees . Using distance formula , find which of them is correct .

Think of this puzzle What do you need to find a chosen number from this square? Four of the clues below are true but do nothing to help in finding the number. Four of the clues are necessary for finding it. Here are eight clues to use: a. The number is greater than 9. b. The number is not a multiple of 10. c. The number is a multiple of 7. d. The number is odd. e. The number is not a multiple of 11. f. The number is less than 200. g. Its ones digit is larger than its tens digit. h. Its tens digit is odd. What is the number? Can you sort out the four clues that help and the four clues that do not help in finding it? First follow the clues and strike off the number which comes out from it. Like - from the first clue we come to know that the number is not from 1 to 9. (strike off numbers from 1 to 9). After completing the puzzle, see which clue is important and which is not?

Analyse the observation table which shows variation of image distance [v] with object distance [u] in the case of a convex lens. Answer the questions that follow without doing any calculations. {:("Sl.No","Object distance","Image distance"),(,"u [cm]","v [cm]"),(1,-90,+18),(2,-60,+20),(3,-30,+30),(4,-20,+60),(5,-18,+90),(6,-10,+100):} (a) What is the focal length of the convex lens ? Given reasons to support your answer. (b) Write the Sl.No of the observation which is not correct. How did you arrive at this conciusion ? (c ) Use an appropriate scale to draw the ray diagram for the observation at Sl. No 4 and find the approximate value of magnification.