Author: L.Saliou. Chall 1 (1)

Challenge 1: Feedback

The aim of this presentation is to demonstrate one correct approach to solving the challenge,

Presentation Structure:

Typical AnswersCollecting Data from the QuestionApplying the FormulaeAnswers AnalysisFast and Furious

Author: L.Saliou. Chall 1 (2)

Challenge 1: Typical Answers

05

1015202530354045

Vote

A4 B1 C1 D6 E1 E3 E6 F1 F2 F3 F4

Location

Challenge 1

Author: L.Saliou. Chall 1 (3)

Challenge 01: Collecting Data from the Question

• The Question was:« A fault has occurred on a token ring network with a radius

of 30m. It uses fibre optic cables which propagate the pulses at one-third of the speed of light. If it takes 1 µs (1E-6) for the pulse to be sent from Node A, and be received back, estimate the sector that contains the fault for the ring given in the Figure. Also estimate the total time that the pulse will take to go round the ring »

• Key words:– Radius of 30m– 1/3 of the speed of light– Time: 1µs (from Node A and back)

Author: L.Saliou. Chall 1 (4)

Challenge 01: Applying the Formulae

• Formulae given in the challenge are:– d = s*(t/2)– P = 2 * r * π

• The speed of light is assumed to be: 3E8 m/s hence here the speed would be:– s = 1E8 m/s

• Hence:– d = 1E8 * (1E-6) / 2 = 0.5 * E(8 + (-6)) = 0.5E2 = 50

meters– P = 2 * 30 * 3.14 = 60 * 3.14 = 188.4 meters

Author: L.Saliou. Chall 1 (5)

Challenge 01: Applying the Formulae

• The best to work out the position is to determine the percent of the perimeter covered by the pulse before reaching the break. Hence:– As 188.4 meters represents 100% of the perimeter– 50 meters represents: location = (50 / 188.4) * 100 = 26%

• Taking the axis (O-A) as the origin it gives us the result F3

• The time to go all around the circle is:– T = d/s = 188.4 / 1E8 ≈ 2µs

Author: L.Saliou. Chall 1 (6)

Challenge 01: Applying the Formulae

20

Node A

0 B

6

5

4

3

2

1

A B C D E F

Author: L.Saliou. Chall 1 (7)

Challenge01: Answers Analysis

Assuming that the perimeter is 188.4 metersWrong answers due to misreading

A4: misreading of the question, the full speed of light was assumed

B1, E1: wrong assumption of half the speed of light

C1: half the speed of light was assumed (speed assumed in the example)

D6, E6: the answer was not 5 meters; misleading power of ten

F1, F2: neither a third or an half of the speed of light was assumed

F4: wrong assumption of a third of the light speed

Author: L.Saliou. Chall 1 (8)

Challenge01: Fast & Furious

Assume the correct distance and π is 3Then the perimeter becomes 180 meters which is close to 200 metersHence 50 div 200 = 25In percent → 25%The answer: F2 or F3As 180 is smaller than 200 the pulse has covered more than 25%

The good answer is F3

Author: L.Saliou. Chall 1 (9)

Challenge 01: Fast & Furious

Assuming time for the pulse to go all around the circle being 2µs

Assuming a break (pulse going in and back) only 50% can be covered

As the half the time is given (1µs) hence the covering is half of 50%

Hence the pulse has covered 25% → F2 or F3

The results are consistent