Thursday, 28 February 2013
DEFECTS OF VISION 2
Defects of vision
Myopia(or) Short sightedness --Human eye can see clearly the objects lying at short distances from it. but not the far off objects
Causes of Myopia
1. Increase in the length of the eye ball as if distance of the retina from the eye has increased.
2. Decrease in focal length of eye lens when the eye is fully relaxed.
Remedy-- To correct a myopic eye, the person has to wear spectacle with a concave lens of suitable focal length.
Hypermetropia (or) Long sightedness-- It is that defect of a human eye in which a person can see clearly the objects lying at large distances from it but the nearby objects cannot be seen clearly.
Causes of Hypermetropia
(1) Decrease in length of eye ball as if distance of retina from the eye lens has decreased
(2) Increase in the focal length of the eye lens when the eye is fully relaxed.
Remedy-- To correct a hypermetropic eye, the person has to wear spectacle with a convex lens of suitable focal length.
Presbyopia-- In this defect old person cannot read and write comfortably.
Cause of Presbiopia--
(1)Gradual weakening of ciliary muscles
(2)Diminishing flexibility of eye lens.
Remedy--An old person has to use spectacles with a convex lens of suitable focal length
When a person suffers from both myopia and hypermetropia his spectacles have bi-focal lenses (i.e) both concave and convex lenses.
AstigmatismThe defect by which the person is notable to differentiate horizontal and vertical position, is called astigmatism.Remedy----It can be rectified by using cylindrical lenses.
STRUCTURE OF HUMAN EYE 2
IMPORTANT POINTS
Eye lens --- double convex lens
The retina --- contains numerous light sensitive cells which generate electrical signals which are sent to brain via optic nerve
Cornea---The transparent spherical membrane covering the front of the eye.
Iris--The coloured diaphragm between the cornea and lens.
Pupil ---The small hole in the iris.
Eye lens--- It is a transparent lens made of jelly like material.
Ciliary muscles--These muscles hold the lens in position.
Retina--The back surface of the eye.
Blind spot--The point at which the optic nerve leaves the eye. An image formed at this point is not sent to the brain.
Aqueous humour---A clear liquid region between the cornea and the lens.
Vitreous humour--The space between eye lens and retina is is filled with another liquid called Vitreous humour.
Persistence of vision--The image of an object seen persists on the retina for 1/16 second even after the removal of the object. This continuance of sensation of eye for some timed is called persistence of vision.
Colour blindness-- It is said to occur when a person cannot distinguish between colours
Accomodation--The ability of the eye to focus both near and distant objects, by adjusting the focal length, is called the accommodation of the eye.
Far Point of the Eye-- It is the farthest point at which the object can be seen clearly. For a normal eye, the far point lies at infinity.
Near point of the Eye-- It is the closest point at which an object can be seen clearly. For normal eye, the near point lies at 25 cm from the eye(least distance of distinct vision).
Wednesday, 27 February 2013
water conservation
Laundry, and Dishes
- 1994 was the year that federally mandated low-flow showerheads, faucets, and toilets started to appear on the scene in significant numbers.
- On average, 10 gallons per day of your water footprint (or 14% of your indoor use) is lost to leaks. Short of installing new water-efficient fixtures, one of the easiest, most effective ways to cut your footprint is by repairing leaky faucets and toilets.
- If you use a low-flow showerhead, you can save 15 gallons of water during a 10-minute shower.
- Every time you shave minutes off your use of hot water, you also save energy and keep dollars in your pocket.
- It takes about 70 gallons of water to fill a bathtub, so showers are generally the more water-efficient way to bathe.
- All of those flushes can add up to nearly 20 gallons a day down the toilet. If you still have a standard toilet, which uses close to 3.5 gallons a flush, you can save by retrofitting or filling your tank with something that will displace some of that water, such as a brick.
- Most front-loading machines are energy- and water-efficient, using just over 20 gallons a load, while most top-loading machines, unless they are energy-efficient, use 40 gallons per load.
- Nearly 22% of indoor home water use comes from doing laundry. Save water by making sure to adjust the settings on your machine to the proper load size.
- Dishwashing is a relatively small part of your water footprint—less than 2% of indoor use—but there are always ways to conserve. Using a machine is actually more water efficient than hand washing, especially if you run full loads.
- Energy Star dishwashers use about 4 gallons of water per load, and even standard machines use only about 6 gallons. Hand washing generally uses about 20 gallons of water each time.
Yards and Pools
- Nearly 60% of a person's household water footprint can go toward lawn and garden maintenance.
- Climate counts—where you live plays a role in how much water you use, especially when it comes to tending to a yard.
- The average pool takes 22,000 gallons of water to fill, and if you don't cover it, hundreds of gallons of water per month can be lost due to evaporation.
Diet
- The water it takes to produce the average American diet alone—approximately 1,000 gallons per person per day—is more than the global average water footprint of 900 gallons per person per day for diet, household use, transportation, energy, and the consumption of material goods.
- That quarter pounder is worth more than 30 average American showers. One of the easiest ways to slim your water footprint is to eat less meat and dairy. Another way is to choose grass-fed, rather than grain-fed, since it can take a lot of water to grow corn and other feed crops.
- A serving of poultry costs about 90 gallons of water to produce. There are also water costs embedded in the transportation of food (gasoline costs water to make). So, consider how far your food has to travel, and buy local to cut your water footprint.
- Pork costs water to produce, and traditional pork production—to make your sausage, bacon, and chops—has also been the cause of some water pollution, as pig waste runs into local water sources.
- On average, a vegan, a person who doesn't eat meat or dairy, indirectly consumes nearly 600 gallons of water per day less than a person who eats the average American diet.
- A cup of coffee takes 55 gallons of water to make, with most of that H2O used to grow the coffee beans.
Electricity, Fuel Economy, and Airline Travel
- The water footprint of your per-day electricity use is based on state averages. If you use alternative energies such as wind and solar, your footprint could be less. (The use of biofuels, however, if they are heavily irrigated, could be another story.) You would also get points, or a footprint reduction, for using energy-star appliances and taking other energy-efficiency measures.
- Washing a car uses about 150 gallons of water, so by washing less frequently you can cut back your water use.
- A gallon of gasoline takes nearly 13 gallons of water to produce. Combine your errands, car pool to work, or take public transportation to reduce both your energy and water use.
- Flying from Los Angeles to San Francisco, about 700 miles round-trip, could cost you more than 9,000 gallons of water, or enough for almost 2,000 average dishwasher loads.
- A cross-country airplane trip (about 6,000 miles) could be worth more than 1,700 standard toilet flushes.
- Traveling from Chicago to Istanbul is just about 10,000 miles round trip, costing enough water to run electricity in the average American home for one person for more than five years.
Industry—Apparel, Home Furnishings, Electronics, and Paper
- According to recent reports, nearly 5% of all U.S. water withdrawals are used to fuel industry and the production of many of the material goods we stock up on weekly, monthly, and yearly.
- It takes about 100 gallons of water to grow and process a single pound of cotton, and the average American goes through about 35 pounds of new cotton material each year. Do you really need that additional T-shirt?
- One of the best ways to conserve water is to buy recycled goods, and to recycle your stuff when you’re done with it. Or, stick to buying only what you really need.
- The water required to create your laptop could wash nearly 70 loads of laundry in a standard machine.
- Recycling a pound of paper, less than the weight of your average newspaper, saves about 3.5 gallons of water. Buying recycled paper products saves water too, as it takes about six gallons of water to produce a dollar worth of paper.
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