When does light refract? when it travels through gases when it crosses the boundary between two types of material light refracts every 2000 wavelengths. when it travels through a vacuum

An observer that stands still as the electron moves by him, will observe

Asmall metal bar, whose initial temperature was 10° c, is dropped into a large container of boiling water. how long will it take the bar to reach 70° c if it is known that its temperature increases 2° during the first second? (the boiling temperature for water is 100° c. round your answer to one decimal place.) sec how long will it take the bar to reach 98° c? (round your answer to one decimal place.)

What will a positive and a negative charge do if they are separated from each other?