Investigating resistance CP9d1 (Edexcel GCSE)

Discussion in 'Supporting Physics' started by Peter Sigsworth, May 17, 2019.

  1. Has anybody run Edexcel CP9d1 – Investigating resistors.

    The instructions show using the following equipment with the attached circuit diagram.


    ● power supply

    ● voltmeter

    ● ammeter

    ● 500 Ω resistor (first resistor)

    ● connectors and wires

    ● 1 kΩ resistor (second resistor)

    There are no tech guides as to what type of meters to use nor the type of power supply.

    We are using ‘TickiT’ voltmeters (0-20v) and ‘TickiT’ ammeters (0.00 -10.00A) with a Philip Harris (UNILAB) 1-13v (ac and dc) 8.5A max power supply.

    We don’t get any readings on the ammeter for either resistor at 7 v or lower and only 0.01A for 12v (nothing lower) on the 1k Ω - only 0.02A for the 500 Ω at 12v , the voltmeter shows (consistently) just under the power supply setting eg 8.4v for a 9v setting.

    Is the resistance too high or are the ammeters not sensitive enough?

    Should I buy and use lower value resistors eg 5 Ω and 10 Ω or buy and use milliammeters.(200mA DC)

    Attached Files:

  2. Nick Mitchener

    Nick Mitchener COMMITTEE

    either use multimeters or lower value resistors. The power supply will usually produce lower than indicated for a DC output if it does both DC and AC.
  3. Thanks for that Nick - we don't want to use multimeters as they are complicated and confusing for less able students to use and what's more important we feel that as far as possible we run the experiment is as close to the instructions as possible - so I guess using milliammeters will get us closest.
  4. Nick Mitchener

    Nick Mitchener COMMITTEE

    That's fine if you have them, but all exam boards allow you to modify experiments to suit available kit. We use low value resistors with high current capacity, low voltage power supplies or batteries, and SATZ meters with two decimal places. We don't do Edexcel, but we rewrite AQA if we don't agree with them or don't have the kit. We have just this week changed all our GCSE ~~IV graph practicals over to using potential dividers to improve the results on the bulb and diode.
  5. You know physics seems to be the worst for this sort of thing - you set things up exactly like they say and it doesn't work!!! The tech support doesn't give any alternatives or guidance - what's the old saying - if its green or moves its biology, if its smelly or explodes its chemistry - if it doesn't work its physics! No wonder students find physics the most difficult of the three sciences.
  6. what type of resistors are you using? we use satz V and A meters, haven't had a complaint well except a lack of 500/470 resistors.
  7. Nick Mitchener

    Nick Mitchener COMMITTEE

    you should get the same, satz are two decimal places so 12/470 = 0.03, 12/1000= 0.01
    6/470=0.01, 6/1000=0.01

    The resistors are incompatible with the meters/power supply.
    Last edited: May 17, 2019
  8. the circuit is


    you change the value on the power supply, then they record amps and calculate resistance (V= I x R)

  9. Lascells 1k Ω 0.5W 20 V max the 500 Ω are Scichem and just say 500 Ω on them
  10. What do you suggest?
  11. These readings are right on the limit for the ammeter so do not give any sort of range - this is about what I get
  12. Nick Mitchener

    Nick Mitchener COMMITTEE

    It isn't about the make of anything, just use ohm's law and you can see that you need milliammeters. Alternatively, resistors are cheap as chips, change resistors.
  13. Thank you. That makes sense - I had toyed with using multlmeters and different resistors - but I want this to be as close to the activity instructions provided as possible.
    I find that if we use equipment which is not shown or different from the instruction sheet then students on the limit of their understand get completely lost and the experiment is wasted with minimum if any learning.
    We have no physics specialists here and I am a lone technician with little if any physics background. That is why it is so important that the author of the practical clearly specifies the correct equipment instead of assuming our knowledge and leaving it up to us to guess what ammeter to use.
    To save over complicating things by using multimeters and resistors which are not as specified, I will purchase at set of milliammeters which is what the author should have specified in the first place.
  14. We have cheap Ammeters (0-2A) and cheap Voltmeters (0-6V). We use 5, 10 and 50 Ohm resistors from Better Equipped and get quite respectable results with 0-7 V settings on the Powerpack ("Retro" - ancient Unilab). :)
  15. Just use the exam boards version of cp5 which just says resistor and use a different value resistor, they need to do the maths V = I x R to calculate the resistance.

    Last edited by a moderator: May 17, 2019
  16. That's great but my point is that the author of the Edexcel practical specified equipment that didn't work - we shouldn't have to mess about with the instructions to get things to work. It isn't rocket science for the author to state use milliammeters or use 5 Ohm and 10 Ohm resistors......or maybe it is rocket science after all!
  17. Paul, those two are different this is the one and it appears that using their set up with a 'normal' ammeter (0-10A) doesn't work because the ammeter range is not low enough

    Last edited by a moderator: May 17, 2019
  18. there is a feedback button in activeteach. I have sent some.
  19. your one is from pearson the publisher, mine are from pearson the exam board.:confused:
  20. i agree, their values are bad.