1 / 20

Uncertainties

Uncertainties. Aims. To be able to calculate the percentage uncertainty of a measurement To be able to combine these uncertainties to evaluate the overall uncertainty in a derived result.

margaritar
Download Presentation

Uncertainties

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Uncertainties

  2. Aims To be able to calculate the percentage uncertainty of a measurement To be able to combine these uncertainties to evaluate the overall uncertainty in a derived result

  3. A Speed camera takes two images of a moving car and works out speed by calculating distance/time. How do you think this image would help somebody appeal their fine in court?

  4. E D C B A

  5. What are Uncertainties? What do you think this is? It is very old! It is GRB 090429B and is thought to be the remnants of one of the first stars born after the Big Bang. It is 13,140,000,000 ± 20,000,000 years old

  6. Calculating Percentage Uncertainties 12.6 V Reading on meter = Finest division = 0.2 V %Uncertainty = Finest Division x 100 Reading Taken % Uncertainty = (0.2/12.6) x 100 = 1.6 %

  7. Task Calculate the percentage uncertainties for the following measurements: 1. 3. 100m record of 9.6 s 1% 0.3% 4. Extension of 0.002m (2mm) 50% 5. Extension of 0.045m (45mm) 2% 2. 0.03%

  8. E D C B A

  9. Combining Uncertainties Suppose I want to work out the density of the block… Mass (kg) = Density Volume (m3) Mass = 0.500 ± 0.001 kg Volume = (6.25 ± 0.25) x 10-5 m3 To Work out the uncertainty in the density, I have to combine the uncertainty in the mass with the uncertainty in the volume

  10. How do we do it? • Work out the Percentage Uncertainty in the volume and the mass. 2. Then add these together.

  11. Work it out… Answer… 4.2%

  12. E D C B A

  13. THE RULES

  14. INSTRUCTIONAL SLIDE Beach Ball Questioning Write about 15 labels to stick on the ball. These should be simple formulae with letters, e.g. AB A/B, X2 , πr2h etc. Stick on labels. Throw ball to a student, student picks label that is nearest left thumb and say how they would calculate the uncertainty. Then throw ball back to you

  15. Independent Learning Task There is a colour coded question grid on your worksheet. You need to choose 3 questions in a line (can be horizontal, vertical, diagonal, doesn’t have to be through the middle box). Beware however… Blue (easy) to Yellow (taxing) to pink (challenging). Blue questions gain 1 mark, yellow gain 2 and pink gain 3 marks. Make sure you clearly label your answers You have 12 minutes

  16. Assessment Swap your work with your partner and assess each others work using the mark scheme. PINK – 3 MARKS YELLOW – 2 MARKS BLUE – 1 MARK Write down your partners mark on the white board and display when asked.

  17. Self Assessment • What did you do well? • What mistakes did you make • How could you improve?

  18. E D C B A

  19. Discussion In your recent experiment about determining the Young Modulus… • What were the most significant sources of uncertainty? • How did you arrive at this decision? • Explain how you would you improve the precision of the final value (lower the combined uncertainty)

  20. E D C B A

More Related