-- when you cool them, their electrical resistance decreases. -- If you make them even colder, their resistance decreases more. -- If you make them even colder, their resistance decreases more. -- If you make them even colder, their resistance decreases more.
-- If you keep making them colder, their resistance keeps decreasing, but it never completely disappears, no matter how cold you make them.
But with a few surprising substances, called 'superconductors' . . .
-- when you cool them, their electrical resistance decreases. -- If you make them even colder, their resistance decreases more. -- If you make them even colder, their resistance decreases more. -- If you make them even colder, their resistance decreases more.
-- If you keep making them colder, then suddenly, at some magic temperature, their resistance COMPLETELY disappears. It doesn't just become small, and it doesn't just become too small to measure. It becomes literally totally and absolutely ZERO.
If you start a current flowing in a superconducting wire, for example, you can connect the ends of the wire together, and the current keeps flowing around and around in it, for months or years. As long as you keep the loop cold enough, the current never decreases, because the superconducting wire has totally ZERO resistance.
Did somebody say "What's this good for ? What can you do with it ?"
1). Every CT-scan machine and every MRI machine needs many powerful magnets to do its thing. They are all electromagnets, with coils of superconducting wire, enclosed in containers full of liquid helium. Yes, it's complicated and expensive. But it turns out to be simpler and cheaper than using regular electromagnets, with coils of regular plain old copper wire, AND the big power supplies that would be needed to keep them going.
2). Resistance in wire means that when current flows through it, energy is lost. The long cables from the power-generating station to your house have resistance, so energy is lost on the way from the generating station to your house. That lost energy is energy that the electric company can't sell, because they can't deliver it to customers.
There are plans to build superconducting cables to carry electric power from the producers to the customers. The cables will be hollow pipes, with liquid helium or liquid hydrogen inside to keep them cold, and something on the outside to insulate them from the warmth outside. Yes, they'll be complicated and expensive. But they'll have ZERO resistance, so NO energy will be lost on its way from the generating stations to the customers. The power companies think they can build superconducting 'transmission lines' that will cost less than the energy that's being lost now, with regular cables.
phenolphthalein indicator is an acid - alkaline organic dye that changes color over a particular pH range depending on the medium. As such , asides phenolphthalein, methyl orange, Alzarian yellow are other indicators that are used during avid - base titration experiment.
In this case, phenolphthalein in an acidic medium is colorless while in basic medium is pink. Also phenolphthalein been a weak acid reacting with the hydroxide thereby reducing the concentration, this will have an effect on the equilibrium position by favoring the forward reaction i.e product formation. hence more products will be formed.
In the case of ammonium chloride, the addition of more ammonium ions results in an increase in the concentration of the products and as such, if more ammonium ions are removed, the equilibrium position will shift to favor the backward reaction i.e reactant formation.
C) A convex lens has a thick center and thin edges; a concave lens has a thin center and thicker edges.
<h3><u>Explanation;</u></h3>
Convex lens refers to the lens which merges the light rays at a particular point, that travels through it, while a concave lens can be identified as the lens which disperses the light rays around, that hits the lenses.
A convex lens is thicker at the center, as compared to its edges, while a concave lens is thinner at the center as compared to its edges.
A concave lens is thicker at the edges than in the middle and spreads light rays apart producing an image smaller than the actual object. A convex lens on the other hand, is thinner at the edges and thicker towards the center, that is they are bent towards a central point.