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# Monthly Archives: June 2012

## Numerical on Eye defect

A myopic eye has a far point of 3m and a near point of 150mm . State the type of spectacle lens needed for viewing an object at normal far point and determine its power in dioptres . Find the near point when wearing this lens ?

## ThinkQuest Competition 2012 – Winners Announced

The thinkquest competition 2012 was held under three categories. The winners of the competition under each category is detailed below.

## ThinkQuest Projects – 19 and Under

### 1st Place – 19 and Under  – World Hunger

Students: Jing Wen Samantha, Yidan, Wie Min, Jie Ying Felicia
Location:Singapore and China
Coach:Ms. Christine Chen
Prize:Laptop computer with approximate retail value of \$1,500 USD, a trip to ThinkQuest Live and \$5,000 USD School Award.

This team harnessed the full potential of the Internet to spread their message about food scarcity. They hope to inspire and encourage others to take part in ending starvation.

### 2nd Place – 19 and UnderVish-Amrit: Transform Poisoned Water Into Nectar

Students:Sitara, Brian, Paridhi, Aadya, Akanksha, Amrit
Location:India (more…)

## Kinematics – Signs of displacement and Velocity

When will displacement and velocity be negative ? Can you explain me about angular acceleration and angular velocity.

[This question was asked via our mobile interface available at http://m.askphysics.com (mobile users visiting www.askphysics.com will be automatically redirected to the mobile version). We are happy that many of our visitors are using the mobile version and utilizing the facilities]

The signs are conventional. We take one direction as positive and the direction opposite to it as negative.

When we discuss one-dimensional motion, it is easy to take the help of the number-line, whatever towards right is positive and towards left is negative. If the initial direction of motion is taken as positive and the further displacements does not make the body to go beyond the initial position in opposite direction, the displacement will be positive.

## ThinkQuest (Think.com) to Announce winners of the contest today

ThinkQuest – An online venture for collaboration of Teachers and Students worldwide organized by Oracle Education Foundation will announce the results of the ThinkQuest Competition today.

First and second place teams from the ThinkQuest International Competition will receive a trip to ThinkQuest Live for themselves, their coach, and one adult chaperone per student. ThinkQuest Live is a five day event hosted by the Oracle Education Foundation in the San Francisco Bay Area, California.

The event includes:

• Educational workshops and activities
• Social events
• Sightseeing excursions
• The elegant and magical ThinkQuest Awards Dinner

The competition was held under 3 categories –

1. ThinkQuest Projects – Develop a website in ThinkQuest Projects.
2. Digital Media – Produce an online journal/blog, a stand-alone website, photo essay, animation, public service announcement, video or some combination of these items.
3. Application Development – Develop an interactive application or game.

The competition started on September 14, 2011 and the deadline for submitting entries was April 25, 2012 at 11:59:59 PM Pacific Daylight Time (PDT)

Today 20 June 2012 is the deadline for declaration of the names of winners.

In India students from Kendriya Vidyalayas and Navodaya Vidyalayas participated in the competition in mass.

See the winners of previous years and their work here at http://www.thinkquest.org/library/winners/2011_projects.html

## What are AXIONS?

Axions are hypothetical particles with a very low mass. According to Einstein, mass is directly related to energy, and therefore very little energy is required to produce axions. “The existence of axions is not proven, but it is considered to be quite likely,” says Daniel Grumiller.

In quantum physics, every particle is described as a wave. The wavelength corresponds to the particle’s energy. Heavy particles have small wavelengths, but the low-energy axions can have wavelengths of many kilometers.

## Force on a current carrying conductor in a magnetic field

Why the force acting on current carrying conductor when placed in a magnetic field increases with the increase in the current.?

I mean what happens inside it at that time? Please explain it in detail, it’s really confusing me, Please answer it as sson as possible.

Let’s consider the terms involved here first.

• Electric Current is the rate of flow of charges. An increase in current through a conductor means more number of electrons are crossing any cross section of the wire per second.
• A moving charge experience a force in magnetic field because a moving charge creates a magnetic field around it. The two interacting magnetic fields causes the force.

So, let’s summarize, when there is a current flowing through a conductor placed in a magnetic field, it experiences a force due to the mutual interaction between the magnetic fields – the already existing field and the field produced by the motion of current carriers (free electrons) inside the conductor.

When there is an increase in current, the force of interaction also increase as the numbers of free electrons flowing through any cross section also increases.

## A thought provoking (HOTS) problem from rotation

Consider a disk rotating in a horizontal plane with a constant angular speed “omega” about its center O.

The disk has a shaded region on one side of the diameter and an unshaded region on the other  side.

When disk is in horizontal plane x-y with left half shaded and right half unshaded, two pebbles P and Q are simultaneously projected at an angle towards R.

The velocity of projection is in the y-z plane and is same for both pebbles with respect to the disk.

Assume that

(i) they land back on the disk before the disk has completed one-eighth rotation,

(ii) their range is less than half the disk  radius,and

(iii)”omega” remains constant throughout.

Then where will the two pebbles land?

(All are invited to answer this)

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