People often use adapters to plug several appliances into the same power socket 

This assessment activity requires you to investigate and explain under what conditions plugging multiple appliances into the same power socket would be dangerous.

You will work in groups of up to three students to carry out experiments and gather data.

You will prepare your report individually.

You will have four to five class periods to complete this work. At the end of each period you will hand in the work you have done. It will be returned to you at the start of the next period.

You will be assessed on how well you are able to use data to explain the impact(s) of plugging additional appliances into a circuit. 

You will not be assessed on the process you use to gather your data.

It is worth 4 credits to you.

Context/setting

In Year 9 or 10, you learnt some basics of electricity.

This assessment activity requires students to show awareness of an aspect of electricity that has an impact on everyday life. 

You will report on the results of a practical experiment with parallel circuits. 

The report will explain the impact of plugging additional appliances resistors into the same circuit, or, in other words, how current varies in a household power socket for different combinations of appliances. 

Hands up who remembers the electricity topic you did in Yr 9 or10?? ...... Thought so = lets do a quick recap of some of the key things you should have learned/remembered. 

Here is a video that summarises the key points you need to remember - take note of how Volts and Current behave in parallel circuits. (Learn)

Here are some of the key pages from your workbook = read and work you way through them. If you are really nice your teacher may make a copy of them for you - or better still dig out your Year 10 workbook and re-read over them. (Learn)

Done that? = Share with your teacher.

Yes = now its time for your next Step/Video clip/Challenge/Mission.

No = go back and complete the Step/Video clip/Challenge/Mission please.

Now there are 7 key learning aspects listed = we are going to work through these one or two at a time. When we've completed all of these you'll be ready to start the assessment.

The key points have been "bolded"

Learning Aspects

This assessment is based on the DC electricity topic of Electricity and Magnetism and before beginning the task, students need to know:

·       how to connect simple series and parallel circuits (a simple parallel circuit is one in which there is no resistor in series with the source)

·       how to use power packs, fuses, resistors, and electrical meters

There are two ways to practice  this - either by using the electricity equipment provided in the lab ......

....... or virtually by using the following link. 

 (To be honest it's easier, quicker and you better results by using the virtual lab.)

Use either either the lab equipment or the virtual lab to build the circuits on the worksheet from your workbook pages. (Create)

Here is a video of how to use this virtual lab - it is pretty straight forward - just watch then go and play. I tend to use the "Lab" option not the "Intro" option - look on the bottom tool bar. (Learn) (Create)

Done that? = Share with your teacher.

Yes = now its time for your next Step/Video clip/Challenge/Mission.

No = go back and complete the Step/Video clip/Challenge/Mission please.

Okay now that you can build simple circuits, we need to master what is actually going on with regard to the volts, current and resistance. In other words "Ohms Law".

·       that current is inversely proportional to resistance for a constant voltage (qualitative knowledge of Ohm’s law V=IR)

Easy just watch this video ..... then go back to your virtual lab (or actual lab) and see for your self. (Learn) (Create)

There is a bit calculating to do ...... here is a link to help with that. 

Or you can play around with the simulator and see how V or I or R changes in relation to each other = change R ..... what happens to V and I etc.

Practice using the law with some of the questions on the workbook pages included above. (Learn)

Done that? = Share with your teacher.

Yes = now its time for your next Step/Video clip/Challenge/Mission.

No = go back and complete the Step/Video clip/Challenge/Mission please.

Next key point is ...

·       that the heating effect in a wire depends on its resistance and therefore the current through it

Have a look at the following video .... (Learn)

So as you can see more current flowing in a circuit causes the wire to heat up. Different components in a circuit or different devices that you can plug in have differing resistances = how much energy electricity needs to get through them. something with high resistance slows down the flow more then something with low resistance.

Have a look at the next couple of pictures. (Learn)

On the left are 2 series circuits, they are quickly built on the virtual lab link above. If you use the link and build the same circuits you'll soon see the effect of changing the resistance. Black lines circle the resistors = second circuit has 3 times the resistance of the first - have a look in the blue circles = the speed of the current in Amps (when you've built the circuits you'll see this too. Circled in red are fuses - increase the voltage and see what happens..... 

If you haven't found out how to do that look at the picture on the right - click on the battery = gets yellow box around it, then move the slider control - red arrow. (Learn) (Create)

Done that? = Share with your teacher.

Yes = now its time for your next Step/Video clip/Challenge/Mission.

No = go back and complete the Step/Video clip/Challenge/Mission please.

The next key points are ....

·       that heat is proportional to power, and power is proportional to current for constant voltage (P = IV), therefore if voltage is constant, increasing total resistance will cool a circuit and decreasing total resistance will heat a circuit.

·       that adding resistance in series increases the total resistance of the circuit, which lowers the current for a given voltage (total resistance is the sum of each resistance in a series circuit)

Lets go back and look at that photo again.... (Learn)

Now if we put together what we saw in the video about the heating effect of current and what is happening in these 2 circuits ...... It will help if you build them .....

Look at the reading on the Ammeters (blue circles) - lower resistance (top circuit) = higher amps = more heat in the wires. 

It's the reverse in the lower circuit - higher resistance = lower current = wires will be cooler.  

You'll see this when you build these circuits = you can "see" the electrons moving quicker. (Learn) (Create)

Done that? = Share with your teacher.

Yes = now its time for your next Step/Video clip/Challenge/Mission.

No = go back and complete the Step/Video clip/Challenge/Mission please.

Final key point is ..... in 2 parts:

·       that adding resistance in parallel lowers the total resistance of the circuit, which increases the current and heat for a given voltage 

and

(total resistance is not the sum of each resistance in a parallel circuit, rather, 1/Rtot = 1/R1 + 1/R2 + … + 1/Rn for n resistors in parallel). 

Okay lets look at the first part = time to build some parallel circuits ..... Have a look at the photo below. (Learn)

Okay so here we have a parallel circuit with 4 branches = go and build it for yourselves. (Create)

In the blue circles we have resistors being added in series = look at the readings on the ammeters .... as we add resistors the current in each branch slows - as we would expect when adding resistors in series.

But - look at the ammeter in the red circle - remember what happens with voltage and current in parallel circuits ..... yes/no ??? Go back and look at the video and workbook pages from your Year 10 work. (Learn)

Done that? = Share with your teacher.

Yes = now its time for your next Step/Video clip/Challenge/Mission.

No = go back and complete the Step/Video clip/Challenge/Mission please.

So if the current goes up ..... what happens to the amount of heat?? Now you can see why there is a fuse in the circuit.

What are fuses? What do they do? Have a look at the next video. (Learn)

So what do fuses look like? Here are some examples that you might commonly find .... (Learn)

This is a ceramic block fuse - it has a thin wire threaded through it = which melts to protect the circuit. You then need to replace the wire to repair the circuit. Usually only found in older houses - often replaced by circuit breakers.

These are circuit breakers - if they get too hot they "trip" and you need to reset them - just like a switch. In the green box = good to go, in the red box these have been tripped and need to be reset.

These a common car fuses, different colours = different size fuse - how much current before it breaks. In the photo on the right you can see the little bit of metal that breaks (melts) when the fuse "blows"

Now for the second bit of the final key point - unlike voltage and current in parallel circuits ..... 

total resistance is not the sum of each resistance in a parallel circuit, rather, 1/Rtot = 1/R1 + 1/R2 + … + 1/Rn for n resistors in parallel

So what does that mean?? its a bit scary looking - have a look and see how this is done. (Learn)

If I put the values into the circuit built before = the example done in the video. 

So for the circuit built before - the total resistance is quite low (4.8 Ohms) (Learn)

Now maybe you can see why we need fuses and why you shouldn't plug too many things into a single socket - which is easily done with a multibox.

Done that? = Share with your teacher.

Yes = now its time for your next Step/Video clip/Challenge/Mission.

No = go back and complete the Step/Video clip/Challenge/Mission please.

Now its time for the assessment .....

Your Teacher will be kind enough to provide you with a copy. Or you can simply read it here and then create a google doc with your answers to share with your teacher.

So lets look at the important points = in bold

People often use adapters to plug several appliances into the same power socket. 

This assessment activity requires you to investigate and explain under what conditions plugging multiple appliances into the same power socket would be dangerous.

Isn't that a bit like what we've just been learning about ....

You will work in groups of up to three students to carry out experiments and gather data.

You will prepare your report individually.

So while you can work in groups to do the practical work ..... you must work alone to write the report.

You will have four to five class periods to complete this work. At the end of each period you will hand in the work you have done. It will be returned to you at the start of the next period.

You will be assessed on how well you are able to use data to explain the impact(s) of plugging additional appliances into a circuit. 

You will need to be using calculations = Ohms Law  etc - to prove what you data says.

You will not be assessed on the process you use to gather your data.

You can use the lab practical equipment or do this online using the virtual lab shared with you.

So what to do next.....

Task

(Key things in bold)

Complete all parts of this task. 

Preparation

The wires that carry current to a power socket are behind the walls of the room. 

The circuit diagram (in your assessment document) shows the wiring between the mains power supply and the socket in the wall. 

Appliances plugged into the same socket connect in parallel.

This is what you learned in Year 10

Imagine someone has plugged three appliances into the power socket shown in the diagram (in your assessment document) above – e.g. a microwave, a blender, and a toaster. 

These appliances have different resistances (blender has the least - microwave the most)

Copy the circuit diagram from above and complete the circuit, showing how the three appliances are connected.

Don't need to use proper circuit symbols - just a clearly labelled diagram.

Done that? = Share with your teacher.

Yes = now its time for your next Step/Video clip/Challenge/Mission.

No = go back and complete the Step/Video clip/Challenge/Mission please.

Gather data

There are two ways to gather the data for this experiment.

Firstly, this can be done individually using the PhET website. 

https://phet.colorado.edu/sims/html/circuit-construction-kit-dc/latest/circuit-construction-kit-dc_en.html

Alternatively, in groups of up to three students, your teacher will supply you with a power pack (the mains supply), three different resistance resistors (the appliances), an ammeter, a voltmeter, and connecting wires.

You are to set up and carry out an experiment that models the appliances being plugged into the socket, one after the other. 

How will you use the components (real or virtual) to represent the 3 appliances?

Record your data in an organised way. If you work in groups, make sure each member of your group agrees on and records the same measurements, with appropriate units. 

 How do you best organise your data? What units should you use?

Your data should allow you to determine:

·       how the currents in the different parts of the circuit change as each additional appliance (resistor) is plugged in.      What do you use to measure current - how do you connect it?

·       how the voltage across the components in the circuit changes.  What do you use to measure voltage - how do you connect it?

·       whether it matters in which order you connect the appliances (resistors)

·       which combinations of one, two, or three appliances are safer than others if the temperature of the wall wires depends on the current flowing through them. How do we keep our wiring safe at home? (Learn) (Create)

Create the following circuits with a 120V battery and an ammeter connected on the branch by the battery. 

Take a screenshot of each circuit.

Make differing circuits using: resistor A (20 Ohms), resistor B (40 Ohms), resistor C (60 Ohms), fuse (10A)

A B C AB AC CB ABC    ACB    BAC BCA   CBA     CAB

ABC with voltmeter measuring each branch = 3x screenshots - with the voltmeter on a different branch each time.

ABC with fuse attached on each branch = 4x screenshots - with the fuse attached into a different branch each time.

Total of 19 screenshots

(Learn) (Create) (Share)

Here is a clue to all of the above ..... 

Or you could use this....

Done that? = Share with your teacher.

Yes = now its time for your next Step/Video clip/Challenge/Mission.

No = go back and complete the Step/Video clip/Challenge/Mission please.

And now for the "Grand Finale" .....

Prepare a report

Working on your own, write a report that shows how the results of your experiment explain the impact that plugging additional appliances into the same circuit will have on everyday life. 

In your report, make sure you use scientific statements, show calculations, and state units, as appropriate. 

Include your data with your report, for assessment.

In your report, make sure you:      This is your checklist.....

·       make appropriate inferences from the data about safety. For example, you could explain under what circumstances you might expect that plugging an additional appliance will or will not be dangerous

What have you learned about current and extra resistance in parallel circuits ....

·       link the data you have gathered to scientific theory you have been taught in class

This is the Ohms Law bit

·       suggest a safety feature that could be built into the circuits of a house to prevent accidents from happening, where the feature should be connected, and how it might work. 

Have a look at what you have at home - usually next to the main switch.

(Learn) (Create) (Share)

Done that? = Share with your teacher.

Yes = now its time for your next Step/Video clip/Challenge/Mission.

No = go back and complete the Step/Video clip/Challenge/Mission please.

Here is your final check list.

 Are you able to tick off all of these ....

Congratulations you are done ..... Sit back ...... Relax ....... and ......