Suppose a beam of electrons is incident on a collection of hydrogen atoms, all of which are in the lowest energy state (n = 1). What is the minimum energy the electrons can have if they are to excite the hydrogen atoms into the n = 2 state?


10.2 eV

Physics & Space Science

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Consider the chimney flue of Figure 2-69. If the Styrofoam is removed and the outer boundary condition is the same, write the necessary node equations and solve for the node temperatures. What is the heat transfer through the chimney flue?

Physics & Space Science

A +2.0-nC point charge is placed at one corner of a square (1.5 m on a side), and a ?3.0-nC charge is placed on a corner diagonally away from the first charge. What is the magnitude of the electric field at either of the two unoccupied corners?

a. 20 N/C b. 14 N/C c. 4.0 N/C d. 12 N/C e. 8.0 N/C

Physics & Space Science

Red-colored diode lasers for pointers and surveying are made from pnjunctions of the compound semiconductor GaAs that has an energy gap of 1.42 eV. What is the wavelength of the light from a GaAs laser?

What will be an ideal response?

Physics & Space Science

How do elliptical galaxies typically compare to spiral galaxies?

A) Elliptical galaxies are redder and rounder. B) Elliptical galaxies are redder and flattened. C) Elliptical galaxies are bluer and rounder. D) Elliptical galaxies are bluer and flattened. E) Elliptical galaxies are always much smaller.

Physics & Space Science