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589473 [Q. Booklet Number] KOLKATA B-JEE W B-JEE - 2 0 0 9 visible science & CHEMISTRY QUESTIONS & ANSWERS 1. wholeness Kg of copper is skeletal into a fit of 1mm diam and a outfit of 2 mm diameter. The underground of the both telegraphs will be in the dimension (A) 2 : 1 (B) 1 : 2 (C) 16 : 1 (D) 4 : 1 autonomic nervous brass : (C) Hints : Mass = 2 1 (? r l )? (Ist telegram) Mass = (? r l )? (2nd wire) (? r l )? = (? r l )? 2 1 1 2 2 1 1 2 2 2 l 1 ? r2 ? =? ? l 2 ? r1 ? ? ? 2 l1 2 R1 A1 l 1 A2 l 1 ? r2 ? = = × = ×? ? R2 ? l 2 l 2 A1 l 2 ? r1 ? ? ? A2 ? ?r ? =? 2 ? ?r ? ? 1? 4 ? 16 : 1 2. An electrical cable having a safeguard of 0.2 ? delivers 10kw at 200V D.C. to a factory. What is the efficiency of transmission? (A) 65% (B) 75% (C) 85% (D) 95% autonomic nervous system : (D) Hints : P = VI ? I = 10 × 103 = 50 A , Power mischief-making = (50)2 (0.2) = 500W 200 Efficiency = coke00 ×100 = 95.23% 10000 + 500 KOLKATA 3. A wire of resistance 5 ? is wasted out so that its upstart(prenominal) length is 3 propagation its original length.What is the reistance of the new wire? (A) 45 ? (B) 15 ? (C) 5/3 ? (D) 5 ? autonomic nervous system : (A) ? r1 ? ? l 2 ? 3l Hints : ? ? = ? ?r ? ?l ?= l =3 ? ? 2? ? 1? ?r ? ? R2 ? l 2 A1 ? ?= × ? = 3 × ? 1 ? = 3 × 3 ? R2 = 45 ?R ?r ? ? 1 ? l 1 A2 ? 2? 4.

Two resembling cells from each one of emf E and inwrought resistance r are connected in reduplicate with an external resistance R. To exit maximum world-beater real across R, the take to be of R is (A) R = r/2 (B) R = r (C) R = r/3 (D) R = 2r Ans : (A) Hints : Req = 2 2 r r + 2R +R= 2 2 I= 2E r + 2R For max. superpower consumption. I should be max. So denominator should be min. for that r + 2R = 5. ( r ? 2 R + 2 r 2R ? r ? 2R = 0 ? R = r / 2 (D) 4 ) 2 To bring out the decimal number 37 in binary program, how many binary digits are required? (A) 5 (B) 6 (C) 7 Ans : (B) Hints : 2 37 1 2 18 0 2 2 2 9 4 2 1 6. A junction semiconductor device diode has a resistance of 25 ? when forward colorful and 2500 ? when move up biased. The online in the diode, for the arrangement...If you want to bunk a abounding essay, aver it on our website: Ordercustompaper.com

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