6 (a) The diagram shows a human eye - Edexcel - GCSE Physics - Question 6 - 2013 - Paper 1

1. Cornea
2. Lens

To calculate the focal length of the lens, we use the lens formula:

$\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$

Where:

• $u = -47 \text{ cm}$ (distance of the object, taken as negative since it is on the same side as the incoming light)
• $v = 20 \text{ cm}$ (distance of the image, taken as positive)

Substituting the values: $\frac{1}{f} = \frac{1}{-47} + \frac{1}{20}$

Calculating the fractions: $\frac{1}{f} = -\frac{1}{47} + \frac{1}{20}$

Combining the fractions: $\frac{1}{f} = \frac{-20 + 47}{940} = \frac{27}{940}$

Now, taking the inverse to find the focal length: $f = \frac{940}{27} \approx 34.81 \text{ cm}$

Thus, the focal length of the lens is approximately 34.81 cm.