One may conceive light to spread successively, by spherical waves. –Christiaan Huygens, 1600s
What theory was Huygens writing about?

the particle theory of light
the reflection of light off objects
the way objects refract light
the wave theory of light

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."

answer by yourhope:

how do models compare to real-world objects?

d. most models represent a real-world object in a simpler way.

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