Question of the Day 25 Nov 2017

Neha's father was reading the manual of a camera which was in very small print. He was not able to read comfortably. Neha had two convex lens A and B of focal length 25 cm and 40 cm respectively. She gave the better of the two lenses to her father. He then read the manual comfortably without any strain in his eyes.

Now answer the following question.
(a) Which one of the two convex lenses did she gave to her father and why?
(b) What is the power of the lens A and B?
(c) What is the range of the distance that his father can keep the manual from the lens for comfortable reading?
(d) Unfortunately while handling the better of the two lenses, it got slipped from her father hand and broke into two piece. Will her father still be able to use the broken pieces for magnifying the small prints? 

Question of the day 15 Nov 2107

Question of the day 15 Nov 2017

A student has two resistors A and B of resistance 4 ohm and 6 ohm respectively.  The student was challenged by the Physics teacher to connect them to a 12 V battery so as to draw maximum current from the voltage source.

How would you advice the student to connect the resistors and what would be the current obtained?

Question of the day 14/11/2017

Question of the day - 14 Nov 2017

The resistance of an electric heating device is 20 ohms. If an electric current of 5 A flows through the device for 30 seconds. Determine

(i) Potential difference applied across the device.

(ii) heat produced in the device in 30 seconds.

The Story of Electricity

THE STORY OF ELECTRICITY

Imagine a world without any electricity. Imagine your home now… no televisions, no air conditioners, no light, no refrigerator, no machines, no mobile phones, no electronic gadgets to assist you, no apps, no facebook, no twitter… The only form of electricity available to us would be that of lightning.

Ohh.. what a boring life…

But life would be very close to nature. Sun and fire will be the only source of light. Watching birds, animals would be your favorite pass time. Crude handmade gadgets like magnetic compass, hammer, knife would be your apps. Pigeon would serve as twitter, FB…

So my dear friend, electricity is an integral part of our modern life. The study of electricity is necessary so that such a vast knowledge is not lost overtime. It must be passed to the next generation.

I am doing my duty as I am passing the story to electricity to you..

Take a piece of copper metal. If you view the copper at the microscopic level you would find a lot of empty space with copper atoms suspended in space in the cloud of electrons. Most of the electrons in the cloud are orbiting to some copper atoms or the other. Some electrons in the cloud are wandering from one atom to the other, colliding with other atoms and electrons. At this microscopic level, everything happens very fast. Electrons are moving at 10⁶m/s, atoms are vibrating very rapidly with a frequency of ……..

Suddenly, in the macroscopic, outer world, a human connected the metal plate to a battery.

In the inner atomic world, there is a change in the scene now. The cloud of wandering electrons  start moving towards positive terminal of the battery with a very slow speed of 1mm/s. The number of wandering electrons are however enormous. About 10²² in few grams of copper.

We call this flow of electrons as electric current.

When such moving electrons are made of pass through a filament of electric bulb, it heats up to approx 2700°C and starts glowing. 

This is how we use electricity of light a bulb.

Watch the video from YouTube to understand electricity in a more detail.