One should not use an umbrella while crossing an open fileld during thunderstorm.

Consider Galileo's method of measuring the speed of light using two lanterns. To get an accuracy of about 10%, the time taken by the experimenter in closing or opening the shutter should be about one tenth of the time taken by the light in going from one experimenter to the other. Assume that it takes 1/100 second for an experimenter to close or open the shutter. How far should the two experimenters be to get a 10% accuracy ? What are the difficulties in having this separation ?

The near and far points of a person are at 40 cm and 250cm respectively. Find the power of the lens he/she should use while reading at 25cm . With this lens on the eye, what maximum distance is clearly visible?

Water vapour comes out from the plant leaf through the stomatal opening. Through the same stomatal opening carbon dioxide diffuses into the plant during photosynthesis. Reason out the above statements using one of the following options:

A railway track (made of iron) is laid in winter when the average temperature is 18^(@)C . The track consists of sections of 12 m placed one after the other. How much gap should be left between two such sections so that there in no compression during summer when the maximum temperature goes to 48^(@)C ? Coefficient of linear expansion of iron = 11 xx 10^(-5)C^(-1) .

Read the following statements and select the correct ones. (i) Electrophoresis is a technique used for the separation of molecules based on their size and charge. (ii) Plasmids are extra-chromosomal, self-replicating, usually circular, double stranded DNA molecules found naturally in many bacteria and also in some yeast,. (iii) It is not advisable to use an exonuclease enzyme while producing a recombinant DNA molecule. (iv) In EcoRl, the roman numberal I indicates that it was the first enzyme isolated from E.coli A) (i) and (ii) B) (iii) and (iv) C) (i),(ii) and (iv) D) (i),(ii),(iii) and (iv)

A transparent paper (refractive index = 1.45) of thickness 0.02 mm is pasted on one of the slits of a Young's double slit experiment which uses monochromatic light of wavelength 620 nm. How many fringes will cross through the centre if the paper is removed ?

Water leaks out from an open tank through a hole of area 2mm^2 in the bottom. Suppose water is filled up to a height of 80 cm and the area of cross section of the tankis 0.4 m^2 . The pressure at the open surface and the hole are equal to the atmospheric pressure. Neglect the small velocity of the water near the open surface in the tank. a. Find the initial speed of water coming out of the hole. b. Findteh speed of water coming out when half of water has leaked out. c. Find the volume of water leaked out during a time interval dt after the height remained is h. Thus find the decrease in height dh in term of h and dt. d. From the result of part c. find the time required for half of the water to leak out.

A beam of light passing from one transparent medium to another obliquely, undergoes an abrupt change in direction. This phenomenon is known as refraction of light. a. Name the law which satisfies during this refraction. b. Draw the figure which shows refraction through a parallel sided glass slab. (Ray passing from air ) c. Using the figure obtaind in (b). Show that the incident ray and the emergent ray are parallel to each other.