题干

在探究凸透镜成像规律的实验中,当烛焰、凸透镜、光屏处于如图所示的位置时,恰能在光屏上得到一个清晰的像.利用这一成像原理的光学仪器是(  )


A:投影仪

B:照相机

C:放大镜

D:显微镜

上一题 下一题 0.0难度 选择题 更新时间:2016-09-05 06:11:07

答案(点此获取答案解析)

B

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How to be a safe and smart SEARCHER

    Several keywords will help to find better results. Use more than one keyword when you are doing a search. If you want to find out about seagulls, for example, search for bird seagull and not just 'seagull' – because seagull might also be the name of just about anything else, from a hotel to a documentary film.

    Exact references can help you find what you're looking for. If you are looking for an exact phrase or sentence, e.g. seagulls are very clever, type it between quotation marks (“”) and only exact matches will be shown. This is useful when you want to find something you've already seen but lost.

Avoid common words like 'a' or 'the' in a search. These aren't always helpful and are usually unnecessary.

    Remove unwanted results by adding a minus symbol (-). For example, seagull-hotel-film would leave out all references to hotels and films.

           ⑷     . Make sure that you spell every word in the search box correctly. The smallest typing mistakes can bring unwanted results - especially when the mistyped word exists.

Have a filter(过滤程序). It's a good idea to filter your searches, especially when you are searching for pictures. Ask an adult to help you add a filtering system. There are lots of filtering software options available.

    Experiment with different search engines until you find the one that's best for you. Some search engines personalise the results. So check out the option of using a search engine that doesn't do this and you will get different results.

    Reliability is very important when you are searching on the Internet. Always ask yourself, “Is this reliable?” Don't make the mistake of believing everything you see. Some websites are unreliable and some information is false. Check your information on other websites before accepting it.