## A-Level Physics teachers: your thoughts welcome

A few months ago, we made a film of an A-level core practical: measuring g via the free-fall method. Many teachers responded to our invitation to comment, and to our shameless request for recommendations for funders. Well… that worked. Thanks for your kind words, and thanks to your kind words we’re making more of these films. We’re not yet revealing the funder, but we can reveal the first three (or four) practicals we’re filming. We’d also like your help again.

We’re filming next weekend, 21st/22nd May, and we’d be delighted if these films could reflect your experience with practicals you’ve completed, your thoughts about ones you’ve yet to teach, and so on. We’ve a crack team of advisors and supporters already involved, but nothing beats the broad experience of teachers across the UK (and internationally).

So: here are the outlines of the films we’re planning to make. Please leave a comment below if you’ve any pertinent thoughts. It’s extremely helpful if you sign your comments with your real name, and note your affiliations (ie. school, that you’re a teacher / head of department / examiner etc) if appropriate. As before, the films are intended primarily to support teachers, but may be of use to students for revision purposes.

### Laser diffraction

• Introduction to traditional two-slit diffraction apparatus, with recap of explanation.
• Plotting slit/screen distance vs. slit spacing.
• Discussion of laser safety issues and suppliers.
• Suggestions around practicalities, and the value of the practical for exploring issues of experiment design.
• Alternative arrangement using a wire rather than traditional double slit.
• Second alternative using diffraction gratings and vertical arrangement.
• (possibly – this film’s already getting quite long!) third alternative using diffraction from a CD, as suggested by OCR.
• Discussion of historical context and significance.

### Finding the EMF and internal resistance of a battery

• Conceptual basis of internal resistance; review of relationship between EMF, terminal potential difference, current and internal resistance.
• Apparatus, using multimeters, variable resistor, bare wire contacts.
• Variations, including array of known resistors; switched contact; analogue meters.
• Comparison of internal resistance of different battery types.
• Discussion of value of this practical for exploring key lab skills, including careful but quick working.

### Discharging a capacitor through a resistor

• Using a data logger to explore capacitor behaviour.
• Initial verification of $$V = V_0 e^{-t/RC}$$; demonstrating that voltage decay half-life is constant, and the time taken to decay to $$1/e$$ of the original value.
• Manipulation of $$V = V_0 e^{-t/RC}$$ to a form comparable with $$y = mx + c$$; processing and plotting data accordingly.
• Low-budget version of practical using voltmeter and stopclock, and with hand-processing of data.
• Extend the practical to finding the value of an unknown capacitor.
• Discussion of error.

### Force on a current-carrying conductor in a magnetic field

• The standard ammeter and balance arrangement.
• Sequence of
• Determining magnetic field strength.
• Alternative arrangement with U-shaped wire segment.

Thanks in advance for all your comments and suggestions. Inevitably, we won’t be able to incorporate everything everybody suggests, but if you’ve come across a brilliant way of covering one of these practicals which we’ve not mentioned above, or have thoughts on aspects your students find particularly challenging – we’ll do our best to incorporate your ideas.

Final note: this post was written by Jonathan. Hello. I’m the film-maker behind all these videos, and while I am technically a physicist, I last saw most of these practicals in my own A-level studies more than 25 years ago. Any glaring howlers in the above are due to my misunderstanding of the scripts, and you can be reasonably confident that the many teachers involved in the filming will politely roll their eyes before we commit film-based crimes against physics.

## Measuring g via Free Fall

Four different approaches to measuring g: try several and prompt your students to think about how they differ in terms of accuracy and repeatability.