In a classroom experiment, a student rubs a comb against her hair. the comb is then brought near bits of paper resting on a surface. which of these can be concluded if the comb picks up the bits of paper?

a) the comb is an insulator, but paper conducts electricity.

b) the comb had a net charge on it, and it attracted a neutral object.

c) the comb was left uncharged, and it attracted a positively charged object.

d) the comb was positively charged, in attracted a negatively charged object

Which type of microscope would allow the viewer to see ribosomes inside a cell?

Comedians like to joke that the reason we haven’t been visited by intelligent life from elsewhere in the universe is that aliens have been monitoring earth’s broadcasts of intellectually embarrassing tv programs, like gilligan’s island, fear factor, the jersey shore, and the jerry springer showand so consider us far too primitive to merit a visit. let’s check the assertion that aliens could have been receiving them. tv programs are broadcast at a frequency of about 100mhz with about 100kw of total power in 30frames per second, which emanatesroughly uniformly in all directions. assume that interstellar space transmits these broadcasts without attenuation. no matter how smart they are, aliens would require at least one photon per frame to interpret our signals. findthe number of photons per unit time per unit area reaching a receiver on a possible planet in the nearest star system, which is about 4 light-years away (a light-year is the distance light travels in a year). if aliens aimed a receiver or detector directly at earth, how big (in diameter) would it have to be to receive a photon per frame

Which terms describe the purpose of antennas on devices that use radio waves? transmit and receivemodify and amplifyamplify and receivemodify and transmit