题干

如图所示是观察水面波衍射的实验装置,AC和BD是两块挡板,AB是一个小孔,O是波源,图中已画出波源所在区域波的传播情况,每两条相邻波纹(图中曲线)之间的距离表示一个波长,则波经过小孔之后的传播情况,下列的描述中正确的是(        )

A:此时不能明显观察到波的衍射现象

B:挡板前后波纹距离相等

C:如果将孔AB扩大,衍射现象会变的更显著

D:如果孔的大小不变,使波源振动频率增大,能更明显观察到衍射现象

上一题 下一题 0.0难度 选择题 更新时间:2019-09-29 07:39:51

答案(点此获取答案解析)

B

同类题4

It's important to teach children to create strong passwords(密码),and to remind them that passwords mustn't be shared with anyone, not even best friends.

A strong password is a word that is as difficult as possible to guess because it looks like a set of random characters (随机的字符).

It's wise to use the whole keyboard to mix a password with letters, numbers and symbols. A password of 14 characters or more may be much safer.

The following tips will tell you how to create a strong and safe password:

Tip 1: Think of a sentence that is easy to remember, but difficult to guess. For example: “ My son Peter is five years old and my daughter Tina is one year old.”The whole sentence is so long that it can't be a password, so what you can do is to use the first letter of each word to make a new password that seems to be meaningless. That is “mspifyoamdtioyo”.

Tip 2: Make the password more difficult to guess by mixing big and small letters. One way to do this is to use big and small letters one after another. In this way this new password will be “MsPiFyOaMdTiOyO”.

Tip 3: Still using the sentence above, you can also add numers that are meaningful to you. As a result, the new password will be “Mspi5yOaMdTi1yO”.

Tip 4: Add punctuation(标点符号)and symbols to make the password much stronger. You may use symbols, numbers and punctuation to replace some letters which look similar. For example: “MsPi3y0@MdTi!y0”.(o=0, a=@, 1=!)

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