题干

氢原子的能级图如图所示,可见光的光子能量范围约为1.62eV~3.11eV,金属钠的逸出功为2.29eV,下列说法中正确的是(  )

A:大量处于n=3能级的氢原子向低能级跃迁时,可发出1种频率的可见光

B:大量处于n=3能级的氢原子向低能级跃迁时,可发出2种频率的可见光

C:大量处于n=3能级的氢原子向低能级跃迁时发出的光当中有1种频率的光能使钠产生光电效应

D:大量处于n=3能级的氢原子向低能级跃迁时发出的光当中有2种频率的光能使钠产生光电效应

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A,D

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    Climbing Without Ropes

    The popular image of the mountain climber is of a person carefully climbing a steep cliff with a network of safety ropes, but it is not the only kind. Many climbers now enjoy bouldering. It's more accessible and better for the environment.

What is bouldering?

Bouldering is a sport that involves climbing on, over, and around boulders up to approximately twenty feet above the ground. Participants employ no safety ropes.

Why boulder?

• improve your climbing skills by focusing on basics

• places to climb, such as climbing walls at gyms and parks, easy to find

• less time commitment to bouldering than to mountain climbing

• intellectual and physical enjoyment as one solves problems


Bouldering Terms

crimp: a very small handhold

foothold: a place where one may place a foot to aid in climbing boulder

jug: a very large handhold that is easy to use

problem: The path up a boulder is referred to as the “problem” that one must solve. The “solution” is the sequence of moves one makes up and over a boulder.

    Here is an example of a climber addressing a bouldering problem.

    Figure 1: The climber has two routes she could take, one to the left and one to the right. The left one appears easier because it has a jug within easy reach, but look what happens if she chooses that direction. She gets stuck on the rock and has to go back down. Sometimes that is even more difficult than going up.

    Figure 2: The climber takes the one to the right this time. Using a foothold and placing her right hand in a crimp, she is able to lift herself up and locate other handholds. After only a few moves, she is able to throw her leg over the top of the boulder and pull herself up.