SAT 2008 - PHYSICS

PHYSICS

Time: ONE Hour
Max. Marks: 60

Answers must be written either in English = or the=20 medium of instruction of the candidate in high school. =

Answer all the questions in the booklets = provided=20 for the purpose.

There will be no negative marking.

The relevant working or the argument in = arriving=20 at an answer has to be included in your answer. =

Use of calculators or graph papers is not = permitted.=20

Questions in Part A carry 6 = marks each=20 and questions in part B carry 3 marks each.=20 =
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Part A

1.Two liquids of masses = 600 g=20 and 500 g and densities 0.6 gcm^-3 and=20 1.5 gcm^-3 are combined to form a homogenous = mixture. A=20 solid block of mass 420 g just floats in this mixture. Find = the=20 density of the block material. If the equal volumes of the two = liquids=20 were mixed instead, would this block float in that mixture? If = it floats=20 find the fraction of the block that is visible above the=20 mixture.

2.A lens of focal = length f produces=20 an image of an object located 30 cm on one side of it at a = distance of=20 60 cm on the other side. If the lens is replaced by another of = 3f/4,=20 where would the image form? If the image has to form at the = earlier=20 position by what distance should the object be = shifted?

3.The devices = D₁ and=20 D₂ shown (below left) are called diodes and have an=20 interesting property. When current flows in the direction of the = arrow=20 the resistance is low and is called forward bias resistance. If = the=20 current were to flow in the opposite direction the resistance is = high=20 and it is called reverse bias resistance. For D₁ = forward bias=20 resistance is 20 Ohm and reverse bias resistance is 600 Ohm. For = D₂ forward bias resistance is 30 Ohm and reverse bias = resistance is 200 Ohm. Find the equivalent resistance between A = and B if=20 (i) A is at a higher potential (ii) B is at a higher=20 potential

4.Rays of light are = incident=20 symmetrically on a sphere of radius R as shown (below middle). = Determine=20 the refractive index of the sphere material if they meet at P = (You need=20 to write the correct expression for refractive index). Can the = rays be=20 made to meet at C, the center of the sphere. If not, how should = the rays=20 be incident to meet at C.

5.If the measured = potential=20 difference between A and B is 5.4 V, Find the rate of heat=20 production in the ring (above right). Also find the rate of heat = production in sections ACB and = ADB.

6.Two identical = rectangular=20 tanks are connected by a small tube at the bottom. In the = left=20 tank contains liquid of density=20 d₁=3D800 kg/m³ to a height=20 h₁=3D30 cm. The right tank contains = liquid of=20 density d₂=3D1600 kg/m³, to a = height=20 h₂=3D20 cm. The two liquids don't = mix. a)=20 Find the heights of the respective columns, if a small = tube=20 connects them at the bottom. b) Where should a horizontal = tube be=20 connected, without causing any flow between the tanks?=20

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Part B

7.Two candles of = identical lengths=20 and different thicknesses were lit. Half of the thin candle and = one=20 third of the thick candle could be seen to burn down in 15 = minutes. How=20 long after the candles had been lit was the ratio of their = lengths=20 4.

8.The average daily = loss of water=20 of a human body is 0.8 kg, evaporated by the body. How much = food=20 has to be consumed in order to compensate for the loss of energy = due to=20 the evaporation if human body can use 70% of the energy provided = by the=20 decomposition of food. The heat of combustion of food is=20 6,000 kJ/kg, the heat of vaporisation of water is=20 2440 kJ/kg

9.A train of length = 300 m=20 passes through two tunnels with a gap of 400 m between them = .The=20 tunnels are of length 800 m and 600 m respectively. = From the=20 moment it just emerges from the first tunnel to the moment it = just=20 disappears in to the second tunnel time elapsed is 60 s. = Find the=20 time elapsed between the moments the train just enters the first = tunnel=20 to the moment it just leaves the second tunnel.

10.Fiber optic cable of = length L=20 has an inner core surrounded by an outer jacket. Light can = travel along=20 the length of the cable through the inner and outer portions. = The=20 refractive indices of the material of the inner and outer = portions are=20 m ₁ and m=20 ₂. Find the time interval between the moments when a = light=20 pulse entering one end of the cable arrives at the other end = traveling=20 through the inner and outer portions.

11.A person's heart does = approximately=20 a work of 1.6 J during a beat. How much work does it do = during a=20 day? By how much does the temperature of 10 kg of water rise if = it=20 absorbs this much of energy?

12.Find the ratio=20 E_i/E_f, where E_i and = E_f are=20 the energies of a neutron before and after interaction with the = nuclei=20 of the moderator in a nuclear reactor.

13.A stone projected = vertically=20 upward on some planet reaches a maximum height h. Find the ratio = of=20 times after projection when it is at a height of = 5h/9.

14.A horizontal = conductor is=20 oriented north south and carries some current. A positively = charged=20 particle located vertically above it and having a velocity = directed=20 northward experiences an upward force. What is the direction of = the=20 force if this charged particle were located to the east of the = conductor=20 and had a velocity directed towards the = conductor.