https://www.physicsforums.com/insights/niches-publishable-undergraduate-research/
Have a look at the article above. Another key point in undergrad research is that you have to read the menu right to left. You cannot pick any topic you want and then figure out if you have the resources to pursue it.
The brainstorming process is greatly streamlined if you first consider the available resources (equipment, mentoring expertise, lab space, group interests, computing facilities and abilities, team abilities) and then focus on the topics for which you have (or can get) the proper resources. For example, if your department has a 1 million frame per second high speed camera available to use, one area of brainstorming becomes, "What interesting and novel things can we do with a high speed camera?" If your faculty mentor is a nuclear physicist who will put most of his equipment at your disposal, you would do well to understand what that equipment is and what may be possible with it. If you have a limited amount of funding (say $2000 US), you need to work with the constraint (as well as the opportunities) of what you can do with $2k. Also, time constraints are huge. A 2 year project window opens up a lot more than a 1 year or a 1 semester project window. If the project needs to be completed by the end of the current semester, your projects will be much more limited than if you have more time.
If resources (equipment and/or time) are more limited,
I've seem some great projects that develop new hypotheses and test them against existing data sets available for download in public repositories. True, it is often preferable to do an original experiment or make an original invention. But often constraints of time and money and safety (some departments won't let undergrads use the fun stuff: radioactive material, high voltage, high vacuum, energetic materials, blast physics, "dangerous" chemicals, etc. without faculty supervision, then they won't provide the supervision they require) greatly narrow the field on the experimental side. There is tons of data available in public repositories. You begin here by first getting a field of some interest (say astrophysics) then having team members research what data is available in that field. Then you float some hypotheses you might be able to test. Then you have a harder look at the available data to consider if one of your hypotheses is really testable.
Another area of low hanging fruit for undergrads is testing whether this or that specialized instrument or other product really meets its product specifications. What is the real accuracy of that spectrum analyzer, precision voltmeter, high vacuum pressure sensor, power meter, or whatever else of key equipment you can get your hands on and figure out how to assess the accuracy of in a reliable manner. Some things we have done is have students measure the breaking strength of fishing line (and compare with the specs) and the drag coefficients of bullets (manufacturers tend to exaggerate). One recent brainstorming idea (more chemistry or biomedical than physics) was testing the accuracy of things like blood glucose monitors (cheap and easy to get at Walmart) and other common and essential biomedical devices. Other (more high school than college) ideas are things like measuring the fuel efficiency of automobiles, testing the accuracy of scales in local supermarkets, and testing the accuracy of the claimed volume on local gasoline pumps. A more physics idea would be to measure if different kinds of batteries really meet their claimed storage specifications.
