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Questions received at Facebook Page

  1. 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?
  2. A system consists of a gas inside a cylinder. Inside the cylinder there is a 10ohm resistor connected to an electrical circuit through which a current can pass. A mass of 0.1 kg is placed on the piston which drops by 0.2m and comes to rest. A current of 0.1 A is passed through the 10 ohm resistor for 2s. What is the change in the internal energy of the system when it has reached equilibrium?
  3. An explosive liquid at temperature 300 K contains a spherical bubbles of radius 5 mm, full of its vapour. When a mechanical shock to the liquid causes adiabatic compression of the bubble, what radius of the bubble is required for combustion of the vapour, given that the vapour ignites spontaneously at 1100 C? The ratio Cv/nR is 3 for the vapour.

photodiode sensor

i want to make a sensor using photodiodes. here photodiodes are connecting parallel and to each photodiode i have to put a load resistance. how can we calculate the value of photo diode? on what basis we can design the load resistance value. i am applying a voltage of 2.5 volt . Is there any method for finding the load resistance value of a photo diode ?

Asked Indira


A spring is held vertically downward and a current is passed through it . Then the length of the spring :

A spring is held vertically downward and a current is passed through it . Then the length of the spring :


A . increases     B. decreases    C . does not change    D the spring oscillates


English: A three-dimensional rendering of a so...




Since the adjacent turns are carrying currents in the same direction (just like two parallel wires) there will be attraction between the turns and therefore the length of the spring



tends to decrease.



How many bulbs can be connected in parallel

English: Incandescent light bulbs.

I need to know how many 15W bulbs can be connected in parallel If I use an extension cord in the 5A socket? If I use the 15 A socket then how many bulbs can I connect in parallel?

Asked Anil


Assuming the voltage to be 220 V,

The current drawn by a single bulb is 15/220=0.068 A

So the no. of bulbs which can be connected in parallel = 5/.068=73 (avoiding the fractional part)

If you use 15A, then 220 bulbs can be connected. (follow the same procedure)

What is the full form of LED?

What is the full form of LED television and also AMOLED?
and which is better and why?

Asks Dipak Kumar

Answer: LED stands for Light Emitting Diode.

LED TVs are actually LED backlit LCD TVs.
Instead of fluorescent tubes, LEDs shine light from behind the screen, illuminating the pixels to create an image. Due to the small size and low power consumption of LEDs, LED-backlit TVs are far thinner than regular LCD sets and are also more energy efficient. They can also provide a (more…)

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