Answer:
The convex lens is shaped so that all light rays that enter it parallel to its axis cross one another at a single point on the opposite side of the lens.
Explanation:
Answer:Simple Covalent substance
Explanation:Simple covalent substance describes a substance that has a low melting point and poor electrical conductivity because:
(1)melting point :For the covalent bond and intermolecular force that are present in a simple covalent substance,energy is needed to break the forces of attraction present. In the simple covalent substance, little energy is needed because the intermolecular forces present are broken because they are weaker compared to the covalent bond present.
Therefore, when simple covalent substance melts,only the intermolecular forces are broken leaving only the covalent bond in the substance.
(2) poor conductivity: for a substance to conduct electricity,it must have charged particles which are free to move to and fro.
But in the simple covalent substance,there are no charged particles that can be separated due to the covalent bond present in simple covalent substance.
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Answer:
At the high temperatures of the inner solar nebula, the small proto-planets were too hot to hold the volatile gases that dominated the solar nebula. These proto-planets were Earth, Mars, Venus, and Mercury.
Explanation:
The materials that accreted into the early Earth were probably added piecemeal, without and particular order. The early earth was very hot from gravitational compression, impacts and radioactive decay; the earth was partially molted. The denser metallic liquids sank to the center of the Earth and less denser silicate liquids rose to the top. In this way the Earth differentiated very quickly into a metallic, mostly iron core and a rocky silicate mantle.
Work done is given by product of force and displacement due to that force
So here we will have

here we know that


Now work done is given as


so it will do 16 J work to move the box