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Energy savings calculation!!

An energy saver light bulb of 11 W gives the same illumination as a conventional 60W light bulb. (a) If a typical light bulb is used on average for five hours a day, how much energy is saved per year by one light-bulb? (b) If each household used eight such light-bulbs, ad there are 20 million households in a country, how much energy would that country save annually?

Asked SNB

led(Answers to this question invited from all users and visitors)

Questions waiting to be answered

Pranav Asked:

What are LED lamps and what is there advantage over other lamps?

Superconductors are those substances that conduct  electricity without any resistance, so why cant we use them in transmitting electricity?

 

Abdul Najeeb asked

i want to know more about Loop quantum gravity and tz implications on gravity, time, space and how will it change our perspective on big bang???????

 

Anju SV asked:

The magnets of earphones are of opposite polarities at left and right ears.why?

Abhijith Asked

Why do we see the same face of moon always?

 

Noel asked:

what is big bang?had it really happened?if it did,where is the proof?is it correct to say that earth and other celestial bodies were formed of this process?

Adarsh Asked:

Why does masses attract each other even though they are separated by even vacuum ?

Aashutoshasked:

why does the earth’s magnetic field flip?

 

Anuja M Bose asked

Is it possible to travel back in time using a time machine and interact with the people who lived in that period?

Vyshakhan asked

1.Is there any body on this universe known to man which is purely frictionless?
2.Is it true that light travels in the same(relative to us) speed even if we are going away from or towards it?Is this proved by experiments and is this phenomena the basis for time travel?

Gokul R Pillaiasked

Sir, I have learnt that the black hole finally opens into a white hole. If it is so, then how much distance would the objects attracted by the black hole travel, before they come out through the white hole?

Questions normally not answered by Students in Viva

Here are some questions which are not properly answered by students during Viva.

  1. Name the Physical quantities to be kept constant for Ohm’s law to be true.
  2. State the Principle of a potentiometer. (The students say that potential drop is proportional to length but the constant quantities are not mentioned)
  3. How can we increase the sensitivity of a potentiometer?
  4. Define figure of merit of a galvanometer.
  5. Which has more resistance – a galvanometer or a milliammeter?
  6. How does an LED emit light?
  7. What is the difference between an ordinary diode and an LED?
  8. Define principal axis of a convex lens?
  9. What happens to the focal length of a concave mirror if it is immersed in water?
  10. What are the factors affecting the intrernal resistance of a cell?
  11. What are the difference between primary and secondary cell?
  12. Why can’t we use a dry cell for starting a car?

Hints/Answers

  1. length, area of cross section,temperature
  2. The potential drop across any length of a conductor of uniform cross section and composition carrying a constant current is directly proportional to the length.
  3. increasing the length of potentiometer wire, decreasing the current, decreasing the potential gradient
  4. Current for unit deflection
  5. galvanometer
  6. The energy released during recombination of electrons and holes across the junction is responsible for the release of light by LED
  7. In ordinary diode the energy emitted during recombination of electrons and holes is in the invisible region of the em spectrum but in the case of LED, the energy is in the visible region.
  8. Straight line joining the centres of curvature of the lens..
  9. The focal length of mirror does not change by changing the medium. Their is a pure geometrical relationship between the radius of curvature and focal length and the relation does not include any term depending on refractive index.
  10. the nature of electrolyte, the concentration of electrolyte, temperature, distance between electrodes, area of electrodes
  11. Primary cell cannot be recharged, secondary cells can be recharged; secondary cells have less internal resistance than primary cells.
  12. Due to the high internal resistance of a dry cell, it won’t be able to provide the current sufficient to start the car
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