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What is alternating current?

What is Alternating Current?&How it works in electric appliances?why don’t we use Direct Current for every appliance?
Asked Prashant Benjamin
Alternating current is defined as the current which changes its direction and magnitude periodically with time.
Alternating current is cheaper to produce and transmit.
The electric appliances depend on one or more of the effects of current like heating effect, chemical effect, magnetic effect etc.
Except where there it requires a unidirectional flow of charges,like chemical effects or electronic devices,  we may use either ac or dc.
In appliances utilizing direction independent effects of current, like heatinf effect, we may use ac or dc.

How is ultrasound used in medical field?

How is ultrasound used in medical field?

Asked Divyashree


Ultrasound are produced by vibrations of frequency more than 20000 Hz. Theya re not heard by us. Ultrasound has got plenty of applications in different fields. The main applications in medical field are:

1. Ultrasonography


A question from electric field

An insulating sphere of mass m and positive charge q is attached to a spring with length h and spring constant k and is at equilibrium. An infinitely long wire with positive linear charge density λ is placed a distance l away from the charged mass at equilibrium (note that the position of the top of the spring is fixed). The previous length of the spring was h. What is the new length of the spring in terms of h, q, k, λ, l as needed.

What is Raman Effect?

Raman effect or Raman scattering is the inelastic scattering of photon (the quantum of light)

This effect was discovered by sir C.V. Raman; hence the name.

English: Raman and Rayleigh scattering process...

The elastic scattering, the commonly observed and most of the photons undergo this, is also called Rayleigh scattering. In this the scattered  photons have the same energy (frequency and wavelength) as the incident photons. But a small fraction of the scattered photons have a different wavelength and frequency. Normally such photons have less frequency (greater wavelength) than the incident photons.

The Raman spectrum of pure water
The Raman spectrum of pure water (Photo credit: The^Bob)

It’s Sir C.V. Raman’s Birthday today – 7 November

Sir C.V. Raman, the Indian physicist whose work was influential in the growth of science in India was born on 7 November 1988. He was the recipient of the Nobel Prize for Physics in 1930 for the discovery that when light traverses a transparent material, some of the deflected light changes in wavelength. This phenomenon is now called Raman scattering and is the result of the Raman effect.


English: Dr. Chandrasekhara Venkata Raman
English: Dr. Chandrasekhara Venkata Raman (Photo credit: Wikipedia)


Venkata Raman was born in Thiruvanaikaval, Trichinopoly, Madras Presidency, in British India to R. Chandrasekhara Iyer (b. 1866) and Parvati Ammal (Saptarshi Parvati).


His father was a lecturer in mathematics and physics at Presidency College in Madras, which Raman entered in 1902 at the age of 13.  In 1904 he passed his B.A. examination in first place and won the gold medal in physics, and in 1907 he gained his M.A. degree with the highest distinctions.


Get more details at http://en.wikipedia.org/wiki/C._V._Raman




Are the gases coming out when a refrigerator is opened vapours?

Are the gases coming out when a refrigerator is opened vapours? Then why is it called?

Asked by a 7th std student.


Air contains humidity (due to the presence of water vapour). Evaporation can take place at any temperature. However the rate of evaporation increases with increase in temperature..

The conversion of a liquid to gas can take place due to evaporation or boiling. but boiling is the phenomenon taking place at a higher but constant temperature.

Due to evaporation (and boiling) the air contains water vapour at room temperature.

When we open the fridge the water vapour condenses to tiny droplets of water and become visible (due to scattering of light).

(I feel that all the concepts might not have been cleared, please ask the questions which arise as comment to this post.)


Why to drink water if it is produced during the chemical reactions during respiration?

Why to drink water if it is produced during the chemical reactions during respiration?

The formula for respiration is:

Glucose + Oxygen –> water + Carbon dioxide + Energy (ATP)

Asked a group of students of class VII, KV AFS Bidar


Water is just a product during respiration. The amount of water obtained during respiration is not sufficient to carry out all the functions. Water has a multitude of functions in human body. See the picture below.


About 78% of human body is water.

The water:

  • Transports nutrients and oxygen into cells
  • Moisturizes the air in lungs
  • Helps with metabolism
  • Protects our vital organ
  • Helps our organs to absorb nutrients better
  • Regulates body temperature
  • Detoxifies
  • Protects and moisturizes our joints

For all the above functions we require more water than produced as a byproduct of respiration.

More details on the role of water in human body can be read from:


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