The spectrum of the sun has hundreds of strong lines of nonionized iron but only a few, very weak lines of helium. a star of spectral type b has very strong lines of helium but very weak iron lines. do these differences mean that the sun contains more iron and less helium than the b star? explain.

How much work is done lifting a 9.10 kg box straight up onto a shelf that is 1.80 m high?

A150 w lamp emits light of wavelength 590 nm uniformly in all directions. what is the photon flux (photons per unit area per unit time) on a small screen at a distance 2.3 m from the lamp? assume the photons are uniformly distributed over the surface of a sphere of radius 2.3 m.

Place several e-field sensors at a few points on different equipotential lines, and look at the relationship between the electric field and the equipotential lines. which statement is true? 1-at any point, the electric field is perpendicular to the equipotential line at that point, and it is directed toward lines of higher voltages. 2-at any point, the electric field is perpendicular to the equipotential line at that point, and it is directed toward lines of lower voltages. 3-at any point, the electric field is parallel to the equipotential line at that point.