5 (a) State one medical use for optical fibres - Edexcel - GCSE Physics - Question 5 - 2017 - Paper 1

The intensity at the end of the fibre is 5.0 W/m². Since 1% of the intensity is lost, we calculate the intensity entering the fibre as follows:

1% of 5.0 W/m² is given by: ext{Loss} = 5.0 imes rac{1}{100} = 0.05 ext{ W/m}²

Thus, the intensity entering the fibre is: $ext{Intensity in} = 5.0 + 0.05 = 5.05 ext{ W/m}²$

To find the power before the intensity loss:

Let it be denoted as $P$ and area $A = 1 ext{ m}²$ (for simplicity). Using the relation: $P = I imes A$ Then: $P = 5.0 ext{ W/m}² imes 1 ext{ m}² = 5.0 ext{ W}$

Now, applying the intensity loss: I_{in} = rac{5.0 ext{ W}}{6.2 imes 10^{-7}} Evaluating this gives: $3.1 imes 10^6 ext{ W}$ Thus, the intensity of the light as it enters the fibre is approximately $5.05 ext{ W/m}²$.