## Why not Physics?

Last month, the Institute of Physics released a report called ‘Why not Physics?

The report looked at how many students studied A-level science subjects in different schools in 2016. The good news is that the picture is a little bit better than when the IOP did a similar analysis 4 years ago.

The bad news is that there are still 44% of schools that don’t send any girls to study A-level Physics*.

As well as looking at the number of students who study physics in different types of schools, the report looks at how well students do in their GCSEs in different subjects, and how that affects their choice of A-levels.

“More girls achieve high grades in GCSE physics than boys, and girls generally outperform boys across the board at GCSE.  However, a smaller proportion of girls have physics in their top four subjects at GCSE (65% for girls compared to 81% for boys). When a student does have physics in their top four results, boys are three times more likely to progress to A-level physics than girls.” pg.18

So, on average, girls tend to be doing well in all of their GCSEs, which means that even though they get a good grade in Physics, they also get good grades in their other subjects, which makes physics less likely to be in their top four subjects.

How do GCSE grades influence what subjects a student chooses at A-level? You might think that students will be more likely choose to study A-levels in subjects that they did well in at GCSE.

You can see in Figure 12 from the report that students are much more likely to study a science A-level if the respective GCSE was in their top 4 results at GCSE.

But what happened if a science was not in a student’s top four subjects.

There is no reason why students have to choose A-levels in subjects that were in their top GCSEs. In fact, there are good reasons relating to progression to university or employment, or simply enjoyment, that mean a student might choose to study an A-level that isn’t in their top 4 GCSEs.

Looking at the graph, boys tend to progress to a science subject that was not in their top 4 at about the same rate regardless of whether it was biology, chemistry or physics.

But wait … Girls are more than twice as likely to choose biology when it wasn’t in their top 4 grades, as they were to choose Physics when it was in their top 4 grades.

Girls are more than twice as likely to choose biology when it wasn’t in their top 4 grades, as they were to choose Physics when it was in their top 4 grades.

Why should this be? Why biology? Why not physics?

One of the recomendations of the IOP report is that:

Schools should provide effective careers guidance that starts at an early stage, focuses on the next educational phase, emphasises the benefit of choosing certain subject combinations to allow progression to a wide variety of opportunities, and actively challenges gender stereotypes and unconscious biases. pg.8

Here at NUSTEM we are working with North East schools to tackle unconscious bias, and minimise its effects on students.  We offer CPD on unconscious bias for teachers, as well as for those who are involved in advising students about A-level and career choice.

If you would be interested in having NUSTEM work with your school on unconscious bias, then get in touch.

*This slightly weird definition means that we can also look at schools which don’t have a sixth form, and track where their pupils go.

## New opportunities: GET North resources, Whole School Gender Equality, Computing resource grants

If you’re the sort of person who’s involved and engaged with NUSTEM’s work, these opportunities might be right up your street:

### Great Exhibition of the North Teaching Resource Creators

The team running GET North 2018 are looking for help developing teaching resource packs for use across England at Key Stages 2 and 3. Separate packs will be produced to tie into the themes of the Exhibition:

• KS2: Science, Art and Design, and Design and Technology
• KS3: Computing, English, and Design and Technology

The organisers are looking to recruit resource creators; professionals who can provide current industry context and support to the resource; and SEN consultants.

Interested? Get the full details and the application form at the GET North website. Deadline 12 noon, 1st December.

### IOP Whole School Gender Equality Programme

The Institute of Physics have a long-running project looking at improving gender balance in physics. Their reports and research are valuable and highly influential (they’ve been a key influence on NUSTEM, for example!). Currently 40 schools are part of a whole-school programme, making small changes in their environment which can lead to big changes in student outlook. Funding has recently been secured to expand this programme.

Participating schools will receive whole-school CPD on unconscious bias and gender equality; can nominate a Gender Champion to attend a free 2-day residential course; and will have access to funding to support further work, including dissemination to other schools and partners.

For further details and the contact email through which to express an interest, see the IOP’s website. Also, do keep us informed (nustem@northumbria.ac.uk), as we’re keen to assist in these efforts ourselves.

### Community Foundation Raspberry Pi kit funding

This just in… the Community Foundation have up to £2,000 available to support the purchase of Raspberry Pi kits and CPD by primary schools, as part of a new project launched recently by Make Stuff NE and Tech for Life. For more information and to apply for funding, click those links. At the time of writing things aren’t quite working correctly; we think the relevant grant scheme may be this one, in which case it’s a very straightforward (online) form.

## Teacher Subject Specialism Training: Secondary Physics

In an attempt to address the shortage of secondary physics teachers, the Department for Education is backing training to support non-physics-specialist teachers (or teachers wishing to return to the profession) in making the transition. A range of training opportunities are available, primarily courses with multiple sessions through the school year from October 2015.

In the North-East, such courses are being offered by George Stephenson High School in Newcastle, The Academy at Shotton Hall, Peterlee (PDF link), The Hermitage Academy in Chester-Le-Street (PDF link), and Carmel College in Darlington (PDF link). We’ve added the first session in the George Stephenson course to our events calendar primarily because we’re hosting it here at Think Lab, but do explore the different opportunities available.

Also be sure to follow the link to the Government page about the scheme. The downloadable training directory there is a bit buggy for me this afternoon, but there appear to be even more opportunities in the North-East than those we highlight above. There are also multiple courses for Maths specialism.

## Evolution CPD

Think Physics, in conjunction with Reading University, is hosting a free CPD session aimed at primary science teachers.

The session will take place on Tuesday 21 April 2015 from 16:30 until 18:30 in Think Lab at Northumbria University.

Light refreshments will be available from 16:00.

The session will be delivered by Chris Hatcher from the University of Reading.

#### Session outline

Evolution and Inheritance will become part of the statutory Science Curriculum for Year 6 students from September 2015. This session will show you ways to bring these tricky concepts to life through hands-on investigations and activities. The team at Reading have developed lesson plans designed to maintain children’s enthusiasm and progress their understanding of evolution while working scientifically. Many of these resources are free to access on their website, and additional resources will be provided in the session. The session also addresses common concerns teachers have about teaching evolution in the classroom and will suggest ways to respond to children’s and parents’ questions.

http://www.eventbrite.co.uk/e/primary-evolution-cpd-tickets-16086800052

Directions to Think Lab can be found here. We look forward to seeing you in April!

## Partnership working

Although the Think Physics project is led by Northumbria University, it is a partnership between 10 different organisations.

This afternoon, I had the pleasure of spending time supporting teachers from one of our partners, North Tyneside Learning Trust.  I was leading a session for primary school teachers about levers, pulleys and gears – which are in the new National Curriculum.

We sorted household objects, created three sorts of catapults, and played with pulleys.  I suspect that I may have lost at least one pingpong ball in the classroom!

The materials from the session are available in here.

## CPD Opportunities in February: KS3/4 Light and Colour, Isaac Physics

We’ve two terrific CPD opportunities coming up late this month, both to be held in our shiny new Think Lab facility at Northumbria University:

## Lights, Camera, Images

26th February, 16:30–18:00
This twilight workshop is aimed at those teaching physics at Key Stages 3 and 4: it’s suitable for non-specialists. We’ll investigate a variety of activities for use in the classroom when teaching light, colour and spectra.

Presented in association with the Institute of Physics.

Light refreshments will be provided on arrival.

## Isaac Physics Day

28th February, 09:00–15:00
This one-day workshop is aimed at A-level Physics teachers and A-level Maths(mechanics units) teachers, or those intending to teach these subjects.

Delivered in association with Isaac Physics, the workshop will support teachers to develop mathematical problem-solving in a physics context. It will also help teachers prepare their students for physics, engineering and maths courses at University.

Refreshments will be provided through out the day.

Isaac Physics Day – brochure.
(PDF, 600Kb).

Please do drop Annie a line if you’ve any further questions, and feel free to pass this information on to anyone else you think might be interested.

## Careers in Initial Teacher Education

Careers in Initial Teacher Education (CITE)

The Careers in Initial Teacher Education (CITE) Project is a collaborative project between NUSTEM and the North East Local Enterprise Partnership (NELEP) funded by the Careers and Enterprise Company.

Due to Covid-19 the training has been moved online.

Session 1 Discussion Slides

Literature Content Analysis Tool

Session 1 Feedback form

Session 2 Discussion slides

Session 2 Feedback form

Session 3 Discussion slides

Session 3 Feedback form

# A-Level Physics Required Practicals: Measuring the EMF and Internal Resistance of a Cell

All the new specifications include “measure the internal resistance of a cell” as one of the practicals. This is probably a new bit of physics for your students, and although the practical is straightforward to set up, collecting and processing the data is more of a challenge. Comparing two different types of cell, as shown in this film, can make the practical more interesting, with potential for differentiation by ability.

## What’s in the Film

The film starts (to 1:24) with the theory which you’ll probably introduce to students before carrying out the practical.

From 1:30 onwards, the film illustrates how you might go about conducting the practical with conventional cells, and also with a button cell (watch battery).

### Safety

Christina and Alom do several things in the film to limit the current so the cell doesn’t overheat: they use a limiting resistor, start with low currents, and connect the circuit only momentarily. This represents safe working practice, but heating the cell would also affect the resistance we’re trying to measure.

### AA Cell

We used a 10 Ω resistor to limit the current in the circuit. A simple fixed resistor would do, but make sure it can handle the maximum power you expect in the circuit – a few Watts. We didn’t have such a resistor to hand for filming, hence the huge switchable resistance box.

To vary the current to get multiple readings we used an old rheostat, rated at about 16 Ω. In practice anything with a range up to 50 Ω or so should work. It’s also possible to use a range of different fixed resistors, or a switchable resistance box.

Digital or analogue voltmeters or ammeters could be used instead of multimeters, but as Christina points out in the film, the use of multimeters is a skill your students will need to develop anyway. Students will need to select the most appropriate range, which is likely to be 20 V DC for the voltmeter and 200 mA DC for the ammeter (taking care to convert back to amps when processing the data).

Alom’s multimeter films may be dull, but they’ve had a third of a million views so… they may have some redeeming merit. Click through to YouTube or to maximise the film from these tiny windows:

#### Collecting & Processing Data

Working in pairs, this experiment can be be done very quickly. Systematic data are nice, but as long as there’s a good spread of data points across the whole range of currents, students should get a good result.

From our data, we arrived at:

y-intercept = 1.415

so:

EMF = 1.415 V
Internal resistance = 2.10 Ω

We would normally expect an AA cell to have an EMF of about 1.5 V and an internal resistance of about 1 Ω. Ours was old and cheap, which probably explains our results: it’s worth noting that poorer-quality cells can make for a more interesting experiment!

• Is their result what they would expect from the cell packaging or label?
• How could they assess the uncertainty in their data?

Christina mentions tolerance at 4’11”, which is a concept with which students may not be familiar. All components have a stated manufacturer’s tolerance, which notes the ±% range which might be expected when the component is in normal use.

### Coin Cell

We used a standard CR2032 watch battery. The readings for this sort of cell vary much more wildly than for an AA cell. We’d assumed this is due to internal heating of the cell, but in writing these notes we’ve started to wonder if it’s more about the chemistry that’s going on inside – if there’s a limit to the reaction rate, that would explain why the voltage drops away rapidly (particularly with high current drain cases), before the cell recovers after ‘resting.’ Comments welcome, and for now we’ll move on…

Taking photos of the meters is one way of dealing with rapidly-changing readings. Another approach would be to use analogue meters, which can be easier to read by eye.

At 6’09” you’ll see Christina using a ‘best fit’ ruler – a clear ruler with a slot through the middle. We recommend these! Our results:

With the increased uncertainty in the readings, Alom suggests repeating the whole experiment twice. Each repeat could be plotted onto the same axes and the gradients and y-intercepts compared. Students could then find the mean EMF and internal resistance, together with their associated uncertainties.

We would normally expect a 3 V cell to have an EMF of about 3 V, and an internal resistance which is much higher than the AA cell – which indeed is what we found, measuring an internal resistance of 15 Ω.

• Is there a better way to record the fluctuating readings?
• Is a simple mean a legitimate way to combine repeat readings?
• What’s the best way to deal with data which looked bunched-up on a graph because you need to include the y-intercept? (You could investigate mathematical extrapolation methods here.)
• Why do cells have different EMFs and internal resistance? What chemicals do they contain and how are they structured inside? (a useful resource here is Battery University, though it gets a little… detailed, shall we say?)

## Other Notes

### Costs

• 50 AA cells should cost about £12.
• 40 3 V coin cells should cost about £5.

### Further Work

Some teachers like to challenge their students further by investigating the EMF and internal resistance of a cell made with copper and zinc electrodes and an item of fruit or a vegetable, for example: a ‘potato battery.’ Further guidance on this can be found at the Practical Physics website. Cutting the potato into different shapes can make for an interesting comparison.

## Assessment

#### Common Practical Assessment Criteria

At the time of writing, the exam boards appear to agree that this practical might be used to address, in whole or in part:

• CPAC 1: Follows written procedures
• Correctly follows instructions to carry out the experimental techniques or procedures
• CPAC 4: Makes and records observations.
• Makes accurate observations relevant to the experimental or investigative procedure.
• Obtains accurate, precise and sufficient data for experimental and investigative procedures and records this methodically using appropriate units and conventions.

You can likely prioritise other CPACs should you so choose. There are some more notes on this in the draft student worksheet, below.

## Student Worksheet

We’ve drafted a student worksheet for this practical, which you may find useful as a starting point:

As ever, no single film can encompass everything one might wish to say about a practical. Please, leave comments with your thoughts about the approach we’ve taken, and your suggestions for alternatives or improvements.

# A-Level Physics Required Practicals: Measuring g using a free fall method

A-level specifications from all the exam boards include “measure the acceleration due to gravity of a freely falling body” as one of the practicals. Students might be a bit uninterested in measuring the value of a constant with which they are already familiar. However, this practical is likely to be undertaken close to the beginning of an A level course. As such, it can be used to make a number of valuable points, each of which is worth introducing our students to at this stage:

• By comparing more than one method, students can practice thinking critically about experimental methods.
• Learn to assess and reduce uncertainty.
• Consider how to present and process data.
• Discuss what is meant by ‘constant.’

## What’s in the Film

The film shows four different methods of measuring g using a falling object:

1. Drop a ball and time its fall with a stopwatch.
2. Drop a ‘g-ball’, which times its own fall.
3. Drop a ball through light gates.
4. Use an electromagnetic switch to release a ball bearing, with triggered timing.

Which of these methods you use might depend on your students’ skill, your own preference, apparatus availability, ease of data collection or processing, and class size. It’s good to compare at least two methods (even if one is shown as a demonstration only), to prompt and inform discussion about precision, accuracy and uncertainty.

#### What’s not in the film

Since we anticipate this practical being used early in the A level course, we’ve not included comments about how to do a full error analysis. There’s more error handling in some of the other films in the series, and we’re planning to complete a film specifically about error as the series continues.

The ASE book The Language of Measurement (£13.50/£8.50 members) refers to precision as:

A measurement is precise if values cluster closely.

In the film, at about 2:22, the word ‘precision’ is used to mean the timer’s smallest scale division. This is us showing our age! A better term might be ‘resolution’.

Other ASE definitions:

Accuracy: a result is accurate if it is close to the true value.

Uncertainty: the interval within which the true value can be expected to lie.

### Calculating g from h and t

Methods 1, 2 and 4 give values of the time $$t$$ for a ball to fall from rest at a height $$h$$. From the equation:

$$s = ut + \frac{1}{2}at^2$$

we have:

$$g = \frac{2h}{t^2}$$

Measuring $$t$$ for different values of $$h$$ allows a graph to be drawn of $$h$$ against $$t^2$$. The gradient of that graph is $$g/2$$.

In method 3 the ball falls through two light gates separated by a distance $$h$$. Each gate gives a value for the average speed of the ball as it passes through, so we can use $$v^2 = u^2 + 2as$$ to find its acceleration between the gates.

### Uncertainties

Uncertainties arise in four ways:

1. Starting the timer.
2. During the ball’s descent, due to air resistance or other factors.
3. Stopping the timer.
4. Determining the height of the fall.

Students can think about these as they compare the different methods. They can try to assess whether each uncertainty will make the values of $$t$$ and $$h$$ too big or too small, or just more uncertain. They can also discuss how each factor will affect the value of $$g$$.

For example: if the measured value of $$t$$ is too big, the calculated value of $$g$$ will be too small, because t is on the bottom line of $$g = 2h/t^2$$.

#### Error in g

Eventually, students must be able to assess the overall uncertainty in their measurements. For example, they might state their measured value as $$g = 8.7 \pm 1~\mathrm{ms^{-2}}$$. For now, however, it is a good start to be able to calculate the percentage error, e.g.:

$$\frac{9.8 – 8.7}{9.8} \times 100\% = 11\%$$

## Method 1: Dropping a ball

Drop a ball from a measured height $$h$$; start and stop a timer to find $$t$$.

Students should be able to comment on the problems with starting and stopping the timer at the correct instants. Reaction time here is not the same as the human response to a random stimulus, since we can watch the ball falling and anticipate the correct moment to stop the timer. It’s still, however, a poor way to measure $$g$$!

Repeated measurements for a fixed value of $$h$$ will give a range of values for $$t$$. Some students may be better at using a consistent technique, which will give a smaller spread in the values of $$t$$. This reduces the random error, but there may still be systematic error, which itself may be revealed by repeating the experiment for different values of $$h$$.

• What’s a better way to release the ball?
• What’s a better way to measure the time?
• Why don’t we try to reduce the uncertainty in measuring $$h$$?

## Method 2: The g-ball

These cost about £20 + VAT from education suppliers, one of which is Timstar.

The g-ball starts timing when released and stops timing as soon as it hits the floor. Like most stopclocks, it measures to a resolution of 0.01 seconds. The switch release can limit accuracy, but overall the g-ball is a quick way to collect a large number of data points. In the film, Alom and Christina use an L-shaped bracket clipped to a metre rule to press the release switch, to aid a clean release.

• How is this better than using a stopwatch?
• How can they ‘average’ their data?

Your students could just repeatedly drop the g-ball from the same height and average all their data, then substitute their average $$t$$ into $$s = \frac{1}{2}gt^2$$ to find $$g$$. Much better would be to exclude anomalous values first, and better still would be to plot a graph of $$h$$ against $$t^2$$ to spot those anomalies.

If you’re going to plot a graph, however, you might as well have two meaningful variables. In the film, Christina and Alom drop the ball from different heights and collect a lot of (not very good!) data quickly.

This approach:

• Helps to spot anomalies visually – an indication of random error.
• Shows that $$g$$ is (more-or-less!) constant: the graph is a straight line.
• Allows $$g$$ to be determined from a gradient, an important skill.
• Might lead on to a discussion about systematic errors (should the graph pass through the origin?).

Systematic errors can often be eliminated by plotting a graph. For example, if the height is measured 1 cm too short each time, the line on the graph will be shifted downwards. The gradient will be unchanged, and the systematic error should be easily detected.

Another approach, incidentally, would be to plot $$2s$$ against $$t^2$$, giving a simpler gradient of $$g$$. This is a matter of personal preference.

#### Language:

Random error: a measurement error due to results varying in an unpredictable way.

Systematic error: A measurement error where results differ from the true value by a consistent amount each time.

## Method 3: Light gates & data logger

Using light gates is a great way to get students familiar with data loggers. Watch out for the common misconception that using a computer will automatically give a better result! In this case, the timing typically does have a higher resolution, and it’s possible to collect lots of data quickly – both good reasons for using the apparatus.

With two light gates, there are three possibilities:

• Display values of $$u$$ and $$v$$, and calculate g using $$v^2 = u^2 + 2as$$.
• Display values of $$u$$, $$v$$ and $$t$$, and calculate g using $$v = u – at$$.
• Position the top light gate just below where the ball is released so the initial velocity is close to zero, then proceed as above.

Note that the measured speeds are always average values, because the ball is accelerating during the time it takes to pass through the light gate.

• Can we be sure that the data logger determines accurate times?
• If we vary $$h$$, what graph should we plot to determine $$g$$?
• How can a graph help to reveal problems with the experimental technique?

#### Apparatus

If you don’t have multiple sets of data loggers, you could have one set up and have students use it in turn. However, the experience of setting up the apparatus is itself valuable, as it prompts the student to think through the role of each piece of equipment rather than to approach the configured apparatus as a ‘black box.’

## Method 4: Electronic Timer

The commercially available apparatus that Alom and Ronan discuss in the film is available from Philip Harris, for about £100+VAT. Instructions for its use are available from the Nuffield Foundation, which also includes circuit diagrams for a DIY version.

Ronan’s version addresses several subtle issues, including that of releasing the ball cleanly, and using a plumb-line to confirm that $$h$$ is being measured vertically. We’ll update this article with more details of Ronan’s apparatus when we have them.

• Between which two points should we measure the height of fall $$h$$?
• Can we be sure that the timer starts and stops at the exact moments we want it to?
• If we vary $$h$$, what graph should we plot to determine $$g$$?

## Assessment

#### Common Practical Assessment Criteria

At the time of writing, the exam boards appear to agree that this practical might be used to address, in whole or in part:

• CPAC 2: Applies investigate approaches and methods when using instruments and equipment.
• CPAC 4: Makes and records observations.

#### Apparatus & Techniques

Each exam board has published a list of apparatus and techniques with which students much be familiar, along with suggestions as to which elements might be addressed by each practical. For example, Edexcel’s guidance for this practical suggests:

• 1. Use appropriate analogue apparatus to record a range of measurements (to include length/distance, temperature, pressure, force, angles, volume) and to interpolate between scale markings
• 2. Use appropriate digital instruments, including electrical multimeters, to obtain a range of measurements (to include time, current, voltage, resistance, mass).
• 4. Use stopwatch or light gates for timing.
• 11. Use ICT such as computer modelling, or datalogger with a variety of sensors to collect data, or use of software to process data.

Check your exam board’s resources: there should be a mapping document to help you decide which criteria to assess on each practical.

## Student Worksheet

We’ve drafted a student worksheet for this practical, which you may find useful: