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Cottage and Small Industries Development Committee to organize National Industrial Goods and Technology Expo
By Glocal Khabar - 2368 0
National Industrial Goods and Technology Expo- Glocal Khabar
Kathmandu, February 19, 2018: Cottage and Small Industries Development Committee is set to organize the twenty-ninth edition of National Industrial Goods and Technology Expo from March 23, 2018 at Bhrikutimandap, Kathmandu.
The motto of the five-day event is ‘Let’s use home-made products, move ahead towards prosperity.’ The committee has shared that handicrafts, wool and bamboo products, goods made from handmade papers, different types of pickles and Palpali Dhaka would be put on display in the expo.
Valleys, waterfalls, flood plains, meanders, and oxbow lakes
If the distance between two charges is halved, the electrical force between them increases by a factor 4.
In fact, the magnitude of the electric force between two charges is given by:

where
k is the Coulomb's constant
q1 and q2 are the two charges
r is the separation between the two charges
We see that the magnitude of the force F is inversely proportional to the square of the distance r. Therefore, if the radius is halved:

the magnitude of the force changes as follows:

so, the force increases by a factor 4.
<em>"A concave lens is thinner at the center than it is at the edges."</em>
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The text does not specify whether the resistance R of the wire must be kept the same or not: here I assume R must be kept the same.
The relationship between the resistance and the resistivity of a wire is

where

is the resistivity
A is the cross-sectional area
R is the resistance
L is the wire length
the cross-sectional area is given by

where r is the radius of the wire. Substituting in the previous equation ,we find

For the new wire, the length L is kept the same (L'=L) while the radius is doubled (r'=2r), so the new resistivity is

Therefore, the new resistivity must be 4 times the original one.