Physicshomework XI-16th march Friday

1. A short-sighted person can see object lying between 10 cm and 20 cm from his eye clearly. (I) What should be the power of the lens he should use (ii) What will be the near point and far point with the lens used. 
2. A convex spherical mirror with a focal length of magnitude 24 cm is placed 20 cm to the left of a plane mirror. An object 0.25 cm tall is placed mid-way between the surface of the plane mirror and the vertex of the spherical mirror. The spherical mirror forms multiple images of the object. Where are two images of the object formed by the spherical mirror that are closest to the spherical mirror, and how tall is each image? 
3. An air bubble inside a glass slab(�=1.5) appears 6 cm when viewed from one side and 4 cm when viewed from opposite side. What is the thickness of slab. 
4. Two capacitors of capacitances 2�F and 5�F respectively are connected in series and combination connected momentarily across a 100V battery. The charged capacitors are now isolated and then connected in parallel, similar charged plates being together. What would be the resulting potential difference across the combination? 
5. Calculate the rms speed of oxygen molecules at STP, the molecular weight of Oxygen being 32. 
6. The silica cylinder of a radiant wall heater is 0.6 m long and has a radius of 5 mm. If it is rated as 1.5 KW, estimate its temperature when operating. (Stefan's constant = 6�10-8 wm-2K-4 ) 
7. A piece of gold-aluminum alloy weighs 100 gm in air and 80 gm in water. What is the weight of the gold in the alloy if the relative density of gold is 19.3 and that of aluminum is 2.5.  
8. What is the power output in horsepower of an electric motor turning at 4800 rev/mins and developing a torque of 4.3 Nm?
9. 
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